This is zsh.info, produced by makeinfo version 7.1 from tzsh.texi. INFO-DIR-SECTION Utilities START-INFO-DIR-ENTRY * ZSH: (zsh). The Z Shell Manual. END-INFO-DIR-ENTRY  File: zsh.info, Node: Top, Next: The Z Shell Manual, Prev: (dir), Up: (dir) The Z Shell Manual ****************** This Info file documents Zsh, a freely available UNIX command interpreter (shell), which of the standard shells most closely resembles the Korn shell (ksh), although it is not completely compatible. Zsh is able to emulate POSIX shells, but its default mode is not POSIX compatible, either. Version 5.9, last updated May 14, 2022. * Menu: * The Z Shell Manual:: * Introduction:: * Roadmap:: * Invocation:: * Files:: * Shell Grammar:: * Redirection:: * Command Execution:: * Functions:: * Jobs & Signals:: * Arithmetic Evaluation:: * Conditional Expressions:: * Prompt Expansion:: * Expansion:: * Parameters:: * Options:: * Shell Builtin Commands:: * Zsh Line Editor:: * Completion Widgets:: * Completion System:: * Completion Using compctl:: * Zsh Modules:: * Calendar Function System:: * TCP Function System:: * Zftp Function System:: * User Contributions:: -- Indices -- * Concept Index:: * Variables Index:: * Options Index:: * Functions Index:: * Editor Functions Index:: * Style and Tag Index:: -- The Detailed Node Listing -- Introduction * Author:: * Availability:: * Mailing Lists:: * The Zsh FAQ:: * The Zsh Web Page:: * The Zsh Userguide:: * See Also:: Invocation * Compatibility:: * Restricted Shell:: Shell Grammar * Simple Commands & Pipelines:: * Precommand Modifiers:: * Complex Commands:: * Alternate Forms For Complex Commands:: * Reserved Words:: * Comments:: * Aliasing:: * Quoting:: Expansion * History Expansion:: * Process Substitution:: * Parameter Expansion:: * Command Substitution:: * Arithmetic Expansion:: * Brace Expansion:: * Filename Expansion:: * Filename Generation:: Parameters * Array Parameters:: * Positional Parameters:: * Local Parameters:: * Parameters Set By The Shell:: * Parameters Used By The Shell:: Options * Specifying Options:: * Description of Options:: * Option Aliases:: * Single Letter Options:: Zsh Line Editor * Keymaps:: * Zle Builtins:: * Zle Widgets:: * User-Defined Widgets:: * Standard Widgets:: * Character Highlighting:: Completion Widgets * Completion Special Parameters:: * Completion Builtin Commands:: * Completion Condition Codes:: * Completion Matching Control:: * Completion Widget Example:: Completion System * Initialization:: * Completion System Configuration:: * Control Functions:: * Bindable Commands:: * Completion Functions:: * Completion Directories:: Completion Using compctl * Command Flags:: * Option Flags:: * Alternative Completion:: * Extended Completion:: * Example:: Zsh Modules * The zsh/attr Module:: * The zsh/cap Module:: * The zsh/clone Module:: * The zsh/compctl Module:: * The zsh/complete Module:: * The zsh/complist Module:: * The zsh/computil Module:: * The zsh/curses Module:: * The zsh/datetime Module:: * The zsh/db/gdbm Module:: * The zsh/deltochar Module:: * The zsh/example Module:: * The zsh/files Module:: * The zsh/langinfo Module:: * The zsh/mapfile Module:: * The zsh/mathfunc Module:: * The zsh/nearcolor Module:: * The zsh/newuser Module:: * The zsh/parameter Module:: * The zsh/pcre Module:: * The zsh/param/private Module:: * The zsh/regex Module:: * The zsh/sched Module:: * The zsh/net/socket Module:: * The zsh/stat Module:: * The zsh/system Module:: * The zsh/net/tcp Module:: * The zsh/termcap Module:: * The zsh/terminfo Module:: * The zsh/watch Module:: * The zsh/zftp Module:: * The zsh/zle Module:: * The zsh/zleparameter Module:: * The zsh/zprof Module:: * The zsh/zpty Module:: * The zsh/zselect Module:: * The zsh/zutil Module:: Calendar Function System * Calendar File and Date Formats:: * Calendar System User Functions:: * Calendar Styles:: * Calendar Utility Functions:: * Calendar Bugs:: TCP Function System * TCP Functions:: * TCP Parameters:: * TCP Examples:: * TCP Bugs:: Zftp Function System * Installation:: * Zftp Functions:: * Miscellaneous Features:: User Contributions * Utilities:: * Recent Directories:: * Other Directory Functions:: * Version Control Information:: * Prompt Themes:: * ZLE Functions:: * Exception Handling:: * MIME Functions:: * Mathematical Functions:: * User Configuration Functions:: * Other Functions::  File: zsh.info, Node: The Z Shell Manual, Next: Introduction, Prev: Top, Up: Top 1 The Z Shell Manual ******************** This document has been produced from the texinfo file zsh.texi, included in the Doc sub-directory of the Zsh distribution. 1.1 Producing documentation from zsh.texi ========================================= The texinfo source may be converted into several formats: The Info manual The Info format allows searching for topics, commands, functions, etc. from the many Indices. The command 'makeinfo zsh.texi' is used to produce the Info documentation. The printed manual The command 'texi2dvi zsh.texi' will output zsh.dvi which can then be processed with ‘dvips’ and optionally ‘gs’ (Ghostscript) to produce a nicely formatted printed manual. The HTML manual An HTML version of this manual is available at the Zsh web site via: . (The HTML version is produced with ‘texi2html’, which may be obtained from . The command is 'texi2html --output . --ifinfo --split=chapter --node-files zsh.texi'. If necessary, upgrade to version 1.78 of texi2html.) For those who do not have the necessary tools to process texinfo, precompiled documentation (PostScript, dvi, PDF, info and HTML formats) is available from the zsh archive site or its mirrors, in the file zsh-doc.tar.gz. (See *note Availability:: for a list of sites.)  File: zsh.info, Node: Introduction, Next: Roadmap, Prev: The Z Shell Manual, Up: Top 2 Introduction ************** Zsh is a UNIX command interpreter (shell) usable as an interactive login shell and as a shell script command processor. Of the standard shells, zsh most closely resembles ‘ksh’ but includes many enhancements. It does not provide compatibility with POSIX or other shells in its default operating mode: see the section *note Compatibility::. Zsh has command line editing, builtin spelling correction, programmable command completion, shell functions (with autoloading), a history mechanism, and a host of other features. * Menu: * Author:: * Availability:: * Mailing Lists:: * The Zsh FAQ:: * The Zsh Web Page:: * The Zsh Userguide:: * See Also::  File: zsh.info, Node: Author, Next: Availability, Up: Introduction 2.1 Author ========== Zsh was originally written by Paul Falstad. Zsh is now maintained by the members of the zsh-workers mailing list . The development is currently coordinated by Peter Stephenson . The coordinator can be contacted at , but matters relating to the code should generally go to the mailing list.  File: zsh.info, Node: Availability, Next: Mailing Lists, Prev: Author, Up: Introduction 2.2 Availability ================ Zsh is available from the following HTTP and anonymous FTP site. The up-to-date source code is available via Git from Sourceforge. See for details. A summary of instructions for the archive can be found at .  File: zsh.info, Node: Mailing Lists, Next: The Zsh FAQ, Prev: Availability, Up: Introduction 2.3 Mailing Lists ================= Zsh has several mailing lists: Announcements about releases, major changes in the shell and the monthly posting of the Zsh FAQ. (moderated) User discussions. Hacking, development, bug reports and patches. Private mailing list (the general public cannot subscribe to it) for discussing bug reports with security implications, i.e., potential vulnerabilities. If you find a security problem in zsh itself, please mail this address. To subscribe or unsubscribe, send mail to the associated administrative address for the mailing list. YOU ONLY NEED TO JOIN ONE OF THE MAILING LISTS AS THEY ARE NESTED. All submissions to ‘zsh-announce’ are automatically forwarded to ‘zsh-users’. All submissions to ‘zsh-users’ are automatically forwarded to ‘zsh-workers’. If you have problems subscribing/unsubscribing to any of the mailing lists, send mail to . The mailing lists are archived; the archives can be accessed via the administrative addresses listed above. There is also a hypertext archive available at .  File: zsh.info, Node: The Zsh FAQ, Next: The Zsh Web Page, Prev: Mailing Lists, Up: Introduction 2.4 The Zsh FAQ =============== Zsh has a list of Frequently Asked Questions (FAQ), maintained by Peter Stephenson . It is regularly posted to the newsgroup ‘comp.unix.shell’ and the ‘zsh-announce’ mailing list. The latest version can be found at any of the Zsh FTP sites, or at . The contact address for FAQ-related matters is .  File: zsh.info, Node: The Zsh Web Page, Next: The Zsh Userguide, Prev: The Zsh FAQ, Up: Introduction 2.5 The Zsh Web Page ==================== Zsh has a web page which is located at . The contact address for web-related matters is .  File: zsh.info, Node: The Zsh Userguide, Next: See Also, Prev: The Zsh Web Page, Up: Introduction 2.6 The Zsh Userguide ===================== A userguide is currently in preparation. It is intended to complement the manual, with explanations and hints on issues where the manual can be cabbalistic, hierographic, or downright mystifying (for example, the word 'hierographic' does not exist). It can be viewed in its current state at . At the time of writing, chapters dealing with startup files and their contents and the new completion system were essentially complete.  File: zsh.info, Node: See Also, Prev: The Zsh Userguide, Up: Introduction 2.7 See Also ============ sh(1), csh(1), tcsh(1), rc(1), bash(1), ksh(1) ‘IEEE Standard for information Technology - Portable Operating System Interface (POSIX) - Part 2: Shell and Utilities’, IEEE Inc, 1993, ISBN 1-55937-255-9.  File: zsh.info, Node: Roadmap, Next: Invocation, Prev: Introduction, Up: Top 3 Roadmap ********* The Zsh Manual, like the shell itself, is large and often complicated. This section of the manual provides some pointers to areas of the shell that are likely to be of particular interest to new users, and indicates where in the rest of the manual the documentation is to be found. 3.1 When the shell starts ========================= When it starts, the shell reads commands from various files. These can be created or edited to customize the shell. See *note Files::. If no personal initialization files exist for the current user, a function is run to help you change some of the most common settings. It won't appear if your administrator has disabled the zsh/newuser module. The function is designed to be self-explanatory. You can run it by hand with 'autoload -Uz zsh-newuser-install; zsh-newuser-install -f'. See also *note User Configuration Functions::. 3.2 Interactive Use =================== Interaction with the shell uses the builtin Zsh Line Editor, ZLE. This is described in detail in *note Zsh Line Editor::. The first decision a user must make is whether to use the Emacs or Vi editing mode as the keys for editing are substantially different. Emacs editing mode is probably more natural for beginners and can be selected explicitly with the command bindkey -e. A history mechanism for retrieving previously typed lines (most simply with the Up or Down arrow keys) is available; note that, unlike other shells, zsh will not save these lines when the shell exits unless you set appropriate variables, and the number of history lines retained by default is quite small (30 lines). See the description of the shell variables (referred to in the documentation as parameters) HISTFILE, HISTSIZE and SAVEHIST in *note Parameters Used By The Shell::. Note that it's currently only possible to read and write files saving history when the shell is interactive, i.e. it does not work from scripts. The shell now supports the UTF-8 character set (and also others if supported by the operating system). This is (mostly) handled transparently by the shell, but the degree of support in terminal emulators is variable. There is some discussion of this in the shell FAQ, . Note in particular that for combining characters to be handled the option COMBINING_CHARS needs to be set. Because the shell is now more sensitive to the definition of the character set, note that if you are upgrading from an older version of the shell you should ensure that the appropriate variable, either LANG (to affect all aspects of the shell's operation) or LC_CTYPE (to affect only the handling of character sets) is set to an appropriate value. This is true even if you are using a single-byte character set including extensions of ASCII such as ISO-8859-1 or ISO-8859-15. See the description of LC_CTYPE in *note Parameters::. 3.2.1 Completion ---------------- Completion is a feature present in many shells. It allows the user to type only a part (usually the prefix) of a word and have the shell fill in the rest. The completion system in zsh is programmable. For example, the shell can be set to complete email addresses in arguments to the mail command from your ~/.abook/addressbook; usernames, hostnames, and even remote paths in arguments to scp, and so on. Anything that can be written in or glued together with zsh can be the source of what the line editor offers as possible completions. Zsh has two completion systems, an old, so called compctl completion (named after the builtin command that serves as its complete and only user interface), and a new one, referred to as compsys, organized as library of builtin and user-defined functions. The two systems differ in their interface for specifying the completion behavior. The new system is more customizable and is supplied with completions for many commonly used commands; it is therefore to be preferred. The completion system must be enabled explicitly when the shell starts. For more information see *note Completion System::. 3.2.2 Extending the line editor ------------------------------- Apart from completion, the line editor is highly extensible by means of shell functions. Some useful functions are provided with the shell; they provide facilities such as: insert-composed-char composing characters not found on the keyboard match-words-by-style configuring what the line editor considers a word when moving or deleting by word history-beginning-search-backward-end, etc. alternative ways of searching the shell history replace-string, replace-pattern functions for replacing strings or patterns globally in the command line edit-command-line edit the command line with an external editor. See *note ZLE Functions:: for descriptions of these. 3.3 Options =========== The shell has a large number of options for changing its behaviour. These cover all aspects of the shell; browsing the full documentation is the only good way to become acquainted with the many possibilities. See *note Options::. 3.4 Pattern Matching ==================== The shell has a rich set of patterns which are available for file matching (described in the documentation as 'filename generation' and also known for historical reasons as 'globbing') and for use when programming. These are described in *note Filename Generation::. Of particular interest are the following patterns that are not commonly supported by other systems of pattern matching: ** for matching over multiple directories | for matching either of two alternatives ~, ^ the ability to exclude patterns from matching when the EXTENDED_GLOB option is set (...) glob qualifiers, included in parentheses at the end of the pattern, which select files by type (such as directories) or attribute (such as size). 3.5 General Comments on Syntax ============================== Although the syntax of zsh is in ways similar to the Korn shell, and therefore more remotely to the original UNIX shell, the Bourne shell, its default behaviour does not entirely correspond to those shells. General shell syntax is introduced in *note Shell Grammar::. One commonly encountered difference is that variables substituted onto the command line are not split into words. See the description of the shell option SH_WORD_SPLIT in *note Parameter Expansion::. In zsh, you can either explicitly request the splitting (e.g. ${=foo}) or use an array when you want a variable to expand to more than one word. See *note Array Parameters::. 3.6 Programming =============== The most convenient way of adding enhancements to the shell is typically by writing a shell function and arranging for it to be autoloaded. Functions are described in *note Functions::. Users changing from the C shell and its relatives should notice that aliases are less used in zsh as they don't perform argument substitution, only simple text replacement. A few general functions, other than those for the line editor described above, are provided with the shell and are described in *note User Contributions::. Features include: promptinit a prompt theme system for changing prompts easily, see *note Prompt Themes:: zsh-mime-setup a MIME-handling system which dispatches commands according to the suffix of a file as done by graphical file managers zcalc a calculator zargs a version of xargs that makes the find command redundant zmv a command for renaming files by means of shell patterns.  File: zsh.info, Node: Invocation, Next: Files, Prev: Roadmap, Up: Top 4 Invocation ************ 4.1 Invocation ============== The following flags are interpreted by the shell when invoked to determine where the shell will read commands from: -c Take the first argument as a command to execute, rather than reading commands from a script or standard input. If any further arguments are given, the first one is assigned to $0, rather than being used as a positional parameter. -i Force shell to be interactive. It is still possible to specify a script to execute. -s Force shell to read commands from the standard input. If the -s flag is not present and an argument is given, the first argument is taken to be the pathname of a script to execute. If there are any remaining arguments after option processing, and neither of the options -c or -s was supplied, the first argument is taken as the file name of a script containing shell commands to be executed. If the option PATH_SCRIPT is set, and the file name does not contain a directory path (i.e. there is no '/' in the name), first the current directory and then the command path given by the variable PATH are searched for the script. If the option is not set or the file name contains a '/' it is used directly. After the first one or two arguments have been appropriated as described above, the remaining arguments are assigned to the positional parameters. For further options, which are common to invocation and the set builtin, see *note Options::. The long option '--emulate' followed (in a separate word) by an emulation mode may be passed to the shell. The emulation modes are those described for the emulate builtin, see *note Shell Builtin Commands::. The '--emulate' option must precede any other options (which might otherwise be overridden), but following options are honoured, so may be used to modify the requested emulation mode. Note that certain extra steps are taken to ensure a smooth emulation when this option is used compared with the emulate command within the shell: for example, variables that conflict with POSIX usage such as path are not defined within the shell. Options may be specified by name using the -o option. -o acts like a single-letter option, but takes a following string as the option name. For example, zsh -x -o shwordsplit scr runs the script scr, setting the XTRACE option by the corresponding letter '-x' and the SH_WORD_SPLIT option by name. Options may be turned _off_ by name by using +o instead of -o. -o can be stacked up with preceding single-letter options, so for example '-xo shwordsplit' or '-xoshwordsplit' is equivalent to '-x -o shwordsplit'. Options may also be specified by name in GNU long option style, '--OPTION-NAME'. When this is done, '-' characters in the option name are permitted: they are translated into '_', and thus ignored. So, for example, 'zsh --sh-word-split' invokes zsh with the SH_WORD_SPLIT option turned on. Like other option syntaxes, options can be turned off by replacing the initial '-' with a '+'; thus '+-sh-word-split' is equivalent to '--no-sh-word-split'. Unlike other option syntaxes, GNU-style long options cannot be stacked with any other options, so for example '-x-shwordsplit' is an error, rather than being treated like '-x --shwordsplit'. The special GNU-style option '--version' is handled; it sends to standard output the shell's version information, then exits successfully. '--help' is also handled; it sends to standard output a list of options that can be used when invoking the shell, then exits successfully. Option processing may be finished, allowing following arguments that start with '-' or '+' to be treated as normal arguments, in two ways. Firstly, a lone '-' (or '+') as an argument by itself ends option processing. Secondly, a special option '--' (or '+-'), which may be specified on its own (which is the standard POSIX usage) or may be stacked with preceding options (so '-x-' is equivalent to '-x --'). Options are not permitted to be stacked after '--' (so '-x-f' is an error), but note the GNU-style option form discussed above, where '--shwordsplit' is permitted and does not end option processing. Except when the ‘sh’/‘ksh’ emulation single-letter options are in effect, the option '-b' (or '+b') ends option processing. '-b' is like '--', except that further single-letter options can be stacked after the '-b' and will take effect as normal. * Menu: * Compatibility:: * Restricted Shell::  File: zsh.info, Node: Compatibility, Next: Restricted Shell, Up: Invocation 4.2 Compatibility ================= Zsh tries to emulate ‘sh’ or ‘ksh’ when it is invoked as sh or ksh respectively; more precisely, it looks at the first letter of the name by which it was invoked, excluding any initial 'r' (assumed to stand for 'restricted'), and if that is 'b', 's' or 'k' it will emulate ‘sh’ or ‘ksh’. Furthermore, if invoked as su (which happens on certain systems when the shell is executed by the su command), the shell will try to find an alternative name from the SHELL environment variable and perform emulation based on that. In ‘sh’ and ‘ksh’ compatibility modes the following parameters are not special and not initialized by the shell: ARGC, argv, cdpath, fignore, fpath, HISTCHARS, mailpath, MANPATH, manpath, path, prompt, PROMPT, PROMPT2, PROMPT3, PROMPT4, psvar, status. The usual zsh startup/shutdown scripts are not executed. Login shells source /etc/profile followed by $HOME/.profile. If the ENV environment variable is set on invocation, $ENV is sourced after the profile scripts. The value of ENV is subjected to parameter expansion, command substitution, and arithmetic expansion before being interpreted as a pathname. Note that the PRIVILEGED option also affects the execution of startup files. The following options are set if the shell is invoked as sh or ksh: NO_BAD_PATTERN, NO_BANG_HIST, NO_BG_NICE, NO_EQUALS, NO_FUNCTION_ARGZERO, GLOB_SUBST, NO_GLOBAL_EXPORT, NO_HUP, INTERACTIVE_COMMENTS, KSH_ARRAYS, NO_MULTIOS, NO_NOMATCH, NO_NOTIFY, POSIX_BUILTINS, NO_PROMPT_PERCENT, RM_STAR_SILENT, SH_FILE_EXPANSION, SH_GLOB, SH_OPTION_LETTERS, SH_WORD_SPLIT. Additionally the BSD_ECHO and IGNORE_BRACES options are set if zsh is invoked as sh. Also, the KSH_OPTION_PRINT, LOCAL_OPTIONS, PROMPT_BANG, PROMPT_SUBST and SINGLE_LINE_ZLE options are set if zsh is invoked as ksh. Please note that, whilst reasonable efforts are taken to address incompatibilities when they arise, zsh does not guarantee complete emulation of other shells, nor POSIX compliance. For more information on the differences between zsh and other shells, please refer to chapter 2 of the shell FAQ, .  File: zsh.info, Node: Restricted Shell, Prev: Compatibility, Up: Invocation 4.3 Restricted Shell ==================== When the basename of the command used to invoke zsh starts with the letter 'r' or the '-r' command line option is supplied at invocation, the shell becomes restricted. Emulation mode is determined after stripping the letter 'r' from the invocation name. The following are disabled in restricted mode: • changing directories with the cd builtin • changing or unsetting the EGID, EUID, GID, HISTFILE, HISTSIZE, IFS, LD_AOUT_LIBRARY_PATH, LD_AOUT_PRELOAD, LD_LIBRARY_PATH, LD_PRELOAD, MODULE_PATH, module_path, PATH, path, SHELL, UID and USERNAME parameters • specifying command names containing / • specifying command pathnames using hash • redirecting output to files • using the exec builtin command to replace the shell with another command • using jobs -Z to overwrite the shell process' argument and environment space • using the ARGV0 parameter to override argv[0] for external commands • turning off restricted mode with set +r or unsetopt RESTRICTED These restrictions are enforced after processing the startup files. The startup files should set up PATH to point to a directory of commands which can be safely invoked in the restricted environment. They may also add further restrictions by disabling selected builtins. Restricted mode can also be activated any time by setting the RESTRICTED option. This immediately enables all the restrictions described above even if the shell still has not processed all startup files. A shell _Restricted Mode_ is an outdated way to restrict what users may do: modern systems have better, safer and more reliable ways to confine user actions, such as _chroot jails_, _containers_ and _zones_. A restricted shell is very difficult to implement safely. The feature may be removed in a future version of zsh. It is important to realise that the restrictions only apply to the shell, not to the commands it runs (except for some shell builtins). While a restricted shell can only run the restricted list of commands accessible via the predefined 'PATH' variable, it does not prevent those commands from running any other command. As an example, if 'env' is among the list of _allowed_ commands, then it allows the user to run any command as 'env' is not a shell builtin command and can run arbitrary executables. So when implementing a restricted shell framework it is important to be fully aware of what actions each of the _allowed_ commands or features (which may be regarded as _modules_) can perform. Many commands can have their behaviour affected by environment variables. Except for the few listed above, zsh does not restrict the setting of environment variables. If a 'perl', 'python', 'bash', or other general purpose interpreted script it treated as a restricted command, the user can work around the restriction by setting specially crafted 'PERL5LIB', 'PYTHONPATH', 'BASHENV' (etc.) environment variables. On GNU systems, any command can be made to run arbitrary code when performing character set conversion (including zsh itself) by setting a 'GCONV_PATH' environment variable. Those are only a few examples. Bear in mind that, contrary to some other shells, 'readonly' is not a security feature in zsh as it can be undone and so cannot be used to mitigate the above. A restricted shell only works if the allowed commands are few and carefully written so as not to grant more access to users than intended. It is also important to restrict what zsh module the user may load as some of them, such as 'zsh/system', 'zsh/mapfile' and 'zsh/files', allow bypassing most of the restrictions.  File: zsh.info, Node: Files, Next: Shell Grammar, Prev: Invocation, Up: Top 5 Files ******* 5.1 Startup/Shutdown Files ========================== Commands are first read from /etc/zshenv; this cannot be overridden. Subsequent behaviour is modified by the RCS and GLOBAL_RCS options; the former affects all startup files, while the second only affects global startup files (those shown here with an path starting with a /). If one of the options is unset at any point, any subsequent startup file(s) of the corresponding type will not be read. It is also possible for a file in $ZDOTDIR to re-enable GLOBAL_RCS. Both RCS and GLOBAL_RCS are set by default. Commands are then read from $ZDOTDIR/.zshenv. If the shell is a login shell, commands are read from /etc/zprofile and then $ZDOTDIR/.zprofile. Then, if the shell is interactive, commands are read from /etc/zshrc and then $ZDOTDIR/.zshrc. Finally, if the shell is a login shell, /etc/zlogin and $ZDOTDIR/.zlogin are read. When a login shell exits, the files $ZDOTDIR/.zlogout and then /etc/zlogout are read. This happens with either an explicit exit via the exit or logout commands, or an implicit exit by reading end-of-file from the terminal. However, if the shell terminates due to exec'ing another process, the logout files are not read. These are also affected by the RCS and GLOBAL_RCS options. Note also that the RCS option affects the saving of history files, i.e. if RCS is unset when the shell exits, no history file will be saved. If ZDOTDIR is unset, HOME is used instead. Files listed above as being in /etc may be in another directory, depending on the installation. As /etc/zshenv is run for all instances of zsh, it is important that it be kept as small as possible. In particular, it is a good idea to put code that does not need to be run for every single shell behind a test of the form 'if [[ -o rcs ]]; then ...' so that it will not be executed when zsh is invoked with the '-f' option. 5.2 Files ========= $ZDOTDIR/.zshenv $ZDOTDIR/.zprofile $ZDOTDIR/.zshrc $ZDOTDIR/.zlogin $ZDOTDIR/.zlogout ${TMPPREFIX}* (default is /tmp/zsh*) /etc/zshenv /etc/zprofile /etc/zshrc /etc/zlogin /etc/zlogout (installation-specific - /etc is the default) Any of these files may be pre-compiled with the zcompile builtin command (*note Shell Builtin Commands::). If a compiled file exists (named for the original file plus the .zwc extension) and it is newer than the original file, the compiled file will be used instead.  File: zsh.info, Node: Shell Grammar, Next: Redirection, Prev: Files, Up: Top 6 Shell Grammar *************** * Menu: * Simple Commands & Pipelines:: * Precommand Modifiers:: * Complex Commands:: * Alternate Forms For Complex Commands:: * Reserved Words:: * Errors:: * Comments:: * Aliasing:: * Quoting::  File: zsh.info, Node: Simple Commands & Pipelines, Next: Precommand Modifiers, Up: Shell Grammar 6.1 Simple Commands & Pipelines =============================== A _simple command_ is a sequence of optional parameter assignments followed by blank-separated words, with optional redirections interspersed. For a description of assignment, see the beginning of *note Parameters::. The first word is the command to be executed, and the remaining words, if any, are arguments to the command. If a command name is given, the parameter assignments modify the environment of the command when it is executed. The value of a simple command is its exit status, or 128 plus the signal number if terminated by a signal. For example, echo foo is a simple command with arguments. A _pipeline_ is either a simple command, or a sequence of two or more simple commands where each command is separated from the next by '|' or '|&'. Where commands are separated by '|', the standard output of the first command is connected to the standard input of the next. '|&' is shorthand for '2>&1 |', which connects both the standard output and the standard error of the command to the standard input of the next. The value of a pipeline is the value of the last command, unless the pipeline is preceded by '!' in which case the value is the logical inverse of the value of the last command. For example, echo foo | sed 's/foo/bar/' is a pipeline, where the output ('foo' plus a newline) of the first command will be passed to the input of the second. If a pipeline is preceded by 'coproc', it is executed as a coprocess; a two-way pipe is established between it and the parent shell. The shell can read from or write to the coprocess by means of the '>&p' and '<&p' redirection operators or with 'print -p' and 'read -p'. A pipeline cannot be preceded by both 'coproc' and '!'. If job control is active, the coprocess can be treated in other than input and output as an ordinary background job. A _sublist_ is either a single pipeline, or a sequence of two or more pipelines separated by '&&' or '||'. If two pipelines are separated by '&&', the second pipeline is executed only if the first succeeds (returns a zero status). If two pipelines are separated by '||', the second is executed only if the first fails (returns a nonzero status). Both operators have equal precedence and are left associative. The value of the sublist is the value of the last pipeline executed. For example, dmesg | grep panic && print yes is a sublist consisting of two pipelines, the second just a simple command which will be executed if and only if the grep command returns a zero status. If it does not, the value of the sublist is that return status, else it is the status returned by the print (almost certainly zero). A _list_ is a sequence of zero or more sublists, in which each sublist is terminated by ';', '&', '&|', '&!', or a newline. This terminator may optionally be omitted from the last sublist in the list when the list appears as a complex command inside '(...)' or '{...}'. When a sublist is terminated by ';' or newline, the shell waits for it to finish before executing the next sublist. If a sublist is terminated by a '&', '&|', or '&!', the shell executes the last pipeline in it in the background, and does not wait for it to finish (note the difference from other shells which execute the whole sublist in the background). A backgrounded pipeline returns a status of zero. More generally, a list can be seen as a set of any shell commands whatsoever, including the complex commands below; this is implied wherever the word 'list' appears in later descriptions. For example, the commands in a shell function form a special sort of list.  File: zsh.info, Node: Precommand Modifiers, Next: Complex Commands, Prev: Simple Commands & Pipelines, Up: Shell Grammar 6.2 Precommand Modifiers ======================== A simple command may be preceded by a _precommand modifier_, which will alter how the command is interpreted. These modifiers are shell builtin commands with the exception of nocorrect which is a reserved word. - The command is executed with a '-' prepended to its argv[0] string. builtin The command word is taken to be the name of a builtin command, rather than a shell function or external command. command [ -pvV ] The command word is taken to be the name of an external command, rather than a shell function or builtin. If the POSIX_BUILTINS option is set, builtins will also be executed but certain special properties of them are suppressed. The -p flag causes a default path to be searched instead of that in $path. With the -v flag, command is similar to whence and with -V, it is equivalent to whence -v. exec [ -cl ] [ -a ARGV0 ] The following command together with any arguments is run in place of the current process, rather than as a sub-process. The shell does not fork and is replaced. The shell does not invoke TRAPEXIT, nor does it source zlogout files. The options are provided for compatibility with other shells. The -c option clears the environment. The -l option is equivalent to the - precommand modifier, to treat the replacement command as a login shell; the command is executed with a - prepended to its argv[0] string. This flag has no effect if used together with the -a option. The -a option is used to specify explicitly the argv[0] string (the name of the command as seen by the process itself) to be used by the replacement command and is directly equivalent to setting a value for the ARGV0 environment variable. nocorrect Spelling correction is not done on any of the words. This must appear before any other precommand modifier, as it is interpreted immediately, before any parsing is done. It has no effect in non-interactive shells. noglob Filename generation (globbing) is not performed on any of the words.  File: zsh.info, Node: Complex Commands, Next: Alternate Forms For Complex Commands, Prev: Precommand Modifiers, Up: Shell Grammar 6.3 Complex Commands ==================== A _complex command_ in zsh is one of the following: if LIST then LIST [ elif LIST then LIST ] ... [ else LIST ] fi The if LIST is executed, and if it returns a zero exit status, the then LIST is executed. Otherwise, the elif LIST is executed and if its status is zero, the then LIST is executed. If each elif LIST returns nonzero status, the else LIST is executed. for NAME ... [ in WORD ... ] TERM do LIST done Expand the list of WORDs, and set the parameter NAME to each of them in turn, executing LIST each time. If the 'in WORD' is omitted, use the positional parameters instead of the WORDs. The TERM consists of one or more newline or ; which terminate the WORDs, and are optional when the 'in WORD' is omitted. More than one parameter NAME can appear before the list of WORDs. If N NAMEs are given, then on each execution of the loop the next N WORDs are assigned to the corresponding parameters. If there are more NAMEs than remaining WORDs, the remaining parameters are each set to the empty string. Execution of the loop ends when there is no remaining WORD to assign to the first NAME. It is only possible for in to appear as the first NAME in the list, else it will be treated as marking the end of the list. for (( [EXPR1] ; [EXPR2] ; [EXPR3] )) do LIST done The arithmetic expression EXPR1 is evaluated first (see *note Arithmetic Evaluation::). The arithmetic expression EXPR2 is repeatedly evaluated until it evaluates to zero and when non-zero, LIST is executed and the arithmetic expression EXPR3 evaluated. If any expression is omitted, then it behaves as if it evaluated to 1. while LIST do LIST done Execute the do LIST as long as the while LIST returns a zero exit status. until LIST do LIST done Execute the do LIST as long as until LIST returns a nonzero exit status. repeat WORD do LIST done WORD is expanded and treated as an arithmetic expression, which must evaluate to a number N. LIST is then executed N times. The repeat syntax is disabled by default when the shell starts in a mode emulating another shell. It can be enabled with the command 'enable -r repeat' case WORD in [ [(] PATTERN [ | PATTERN ] ... ) LIST (;;|;&|;|) ] ... esac Execute the LIST associated with the first PATTERN that matches WORD, if any. The form of the patterns is the same as that used for filename generation. See *note Filename Generation::. Note further that, unless the SH_GLOB option is set, the whole pattern with alternatives is treated by the shell as equivalent to a group of patterns within parentheses, although white space may appear about the parentheses and the vertical bar and will be stripped from the pattern at those points. White space may appear elsewhere in the pattern; this is not stripped. If the SH_GLOB option is set, so that an opening parenthesis can be unambiguously treated as part of the case syntax, the expression is parsed into separate words and these are treated as strict alternatives (as in other shells). If the LIST that is executed is terminated with ;& rather than ;;, the following list is also executed. The rule for the terminator of the following list ;;, ;& or ;| is applied unless the esac is reached. If the LIST that is executed is terminated with ;| the shell continues to scan the PATTERNs looking for the next match, executing the corresponding LIST, and applying the rule for the corresponding terminator ;;, ;& or ;|. Note that WORD is not re-expanded; all applicable PATTERNs are tested with the same WORD. select NAME [ in WORD ... TERM ] do LIST done where TERM is one or more newline or ; to terminate the WORDs. Print the set of WORDs, each preceded by a number. If the in WORD is omitted, use the positional parameters. The PROMPT3 prompt is printed and a line is read from the line editor if the shell is interactive and that is active, or else standard input. If this line consists of the number of one of the listed WORDs, then the parameter NAME is set to the WORD corresponding to this number. If this line is empty, the selection list is printed again. Otherwise, the value of the parameter NAME is set to null. The contents of the line read from standard input is saved in the parameter REPLY. LIST is executed for each selection until a break or end-of-file is encountered. ( LIST ) Execute LIST in a subshell. Traps set by the trap builtin are reset to their default values while executing LIST; an exception is that ignored signals will continue to be ignored if the option POSIXTRAPS is set. { LIST } Execute LIST. { TRY-LIST } always { ALWAYS-LIST } First execute TRY-LIST. Regardless of errors, or break or continue commands encountered within TRY-LIST, execute ALWAYS-LIST. Execution then continues from the result of the execution of TRY-LIST; in other words, any error, or break or continue command is treated in the normal way, as if ALWAYS-LIST were not present. The two chunks of code are referred to as the 'try block' and the 'always block'. Optional newlines or semicolons may appear after the always; note, however, that they may _not_ appear between the preceding closing brace and the always. An 'error' in this context is a condition such as a syntax error which causes the shell to abort execution of the current function, script, or list. Syntax errors encountered while the shell is parsing the code do not cause the ALWAYS-LIST to be executed. For example, an erroneously constructed if block in TRY-LIST would cause the shell to abort during parsing, so that ALWAYS-LIST would not be executed, while an erroneous substitution such as ${*foo*} would cause a run-time error, after which ALWAYS-LIST would be executed. An error condition can be tested and reset with the special integer variable TRY_BLOCK_ERROR. Outside an ALWAYS-LIST the value is irrelevant, but it is initialised to -1. Inside ALWAYS-LIST, the value is 1 if an error occurred in the TRY-LIST, else 0. If TRY_BLOCK_ERROR is set to 0 during the ALWAYS-LIST, the error condition caused by the TRY-LIST is reset, and shell execution continues normally after the end of ALWAYS-LIST. Altering the value during the TRY-LIST is not useful (unless this forms part of an enclosing always block). Regardless of TRY_BLOCK_ERROR, after the end of ALWAYS-LIST the normal shell status $? is the value returned from TRY-LIST. This will be non-zero if there was an error, even if TRY_BLOCK_ERROR was set to zero. The following executes the given code, ignoring any errors it causes. This is an alternative to the usual convention of protecting code by executing it in a subshell. { # code which may cause an error } always { # This code is executed regardless of the error. (( TRY_BLOCK_ERROR = 0 )) } # The error condition has been reset. When a try block occurs outside of any function, a return or a exit encountered in TRY-LIST does _not_ cause the execution of ALWAYS-LIST. Instead, the shell exits immediately after any EXIT trap has been executed. Otherwise, a return command encountered in TRY-LIST will cause the execution of ALWAYS-LIST, just like break and continue. function [ -T ] WORD ... [ () ] [ TERM ] { LIST } WORD ... () [ TERM ] { LIST } WORD ... () [ TERM ] COMMAND where TERM is one or more newline or ;. Define a function which is referenced by any one of WORD. Normally, only one WORD is provided; multiple WORDs are usually only useful for setting traps. The body of the function is the LIST between the { and }. See *note Functions::. The options of function have the following meanings: -T Enable tracing for this function, as though with functions -T. See the documentation of the -f option to the typeset builtin, in *note Shell Builtin Commands::. If the option SH_GLOB is set for compatibility with other shells, then whitespace may appear between the left and right parentheses when there is a single WORD; otherwise, the parentheses will be treated as forming a globbing pattern in that case. In any of the forms above, a redirection may appear outside the function body, for example func() { ... } 2>&1 The redirection is stored with the function and applied whenever the function is executed. Any variables in the redirection are expanded at the point the function is executed, but outside the function scope. time [ PIPELINE ] The PIPELINE is executed, and timing statistics are reported on the standard error in the form specified by the TIMEFMT parameter. If PIPELINE is omitted, print statistics about the shell process and its children. [[ EXP ]] Evaluates the conditional expression EXP and return a zero exit status if it is true. See *note Conditional Expressions:: for a description of EXP.  File: zsh.info, Node: Alternate Forms For Complex Commands, Next: Reserved Words, Prev: Complex Commands, Up: Shell Grammar 6.4 Alternate Forms For Complex Commands ======================================== Many of zsh's complex commands have alternate forms. These are non-standard and are likely not to be obvious even to seasoned shell programmers; they should not be used anywhere that portability of shell code is a concern. The short versions below only work if SUBLIST is of the form '{ LIST }' or if the SHORT_LOOPS option is set. For the if, while and until commands, in both these cases the test part of the loop must also be suitably delimited, such as by '[[ ... ]]' or '(( ... ))', else the end of the test will not be recognized. For the for, repeat, case and select commands no such special form for the arguments is necessary, but the other condition (the special form of SUBLIST or use of the SHORT_LOOPS option) still applies. The SHORT_REPEAT option is available to enable the short version only for the repeat command. if LIST { LIST } [ elif LIST { LIST } ] ... [ else { LIST } ] An alternate form of if. The rules mean that if [[ -o ignorebraces ]] { print yes } works, but if true { # Does not work! print yes } does _not_, since the test is not suitably delimited. if LIST SUBLIST A short form of the alternate if. The same limitations on the form of LIST apply as for the previous form. for NAME ... ( WORD ... ) SUBLIST A short form of for. for NAME ... [ in WORD ... ] TERM SUBLIST where TERM is at least one newline or ;. Another short form of for. for (( [EXPR1] ; [EXPR2] ; [EXPR3] )) SUBLIST A short form of the arithmetic for command. foreach NAME ... ( WORD ... ) LIST end Another form of for. while LIST { LIST } An alternative form of while. Note the limitations on the form of LIST mentioned above. until LIST { LIST } An alternative form of until. Note the limitations on the form of LIST mentioned above. repeat WORD SUBLIST This is a short form of repeat. case WORD { [ [(] PATTERN [ | PATTERN ] ... ) LIST (;;|;&|;|) ] ... } An alternative form of case. select NAME [ in WORD ... TERM ] SUBLIST where TERM is at least one newline or ;. A short form of select. function WORD ... [ () ] [ TERM ] SUBLIST This is a short form of function.  File: zsh.info, Node: Reserved Words, Next: Errors, Prev: Alternate Forms For Complex Commands, Up: Shell Grammar 6.5 Reserved Words ================== The following words are recognized as reserved words when used as the first word of a command unless quoted or disabled using disable -r: do done esac then elif else fi for case if while function repeat time until select coproc nocorrect foreach end ! [[ { } declare export float integer local readonly typeset Additionally, '}' is recognized in any position if neither the IGNORE_BRACES option nor the IGNORE_CLOSE_BRACES option is set.  File: zsh.info, Node: Errors, Next: Comments, Prev: Reserved Words, Up: Shell Grammar 6.6 Errors ========== Certain errors are treated as fatal by the shell: in an interactive shell, they cause control to return to the command line, and in a non-interactive shell they cause the shell to be aborted. In older versions of zsh, a non-interactive shell running a script would not abort completely, but would resume execution at the next command to be read from the script, skipping the remainder of any functions or shell constructs such as loops or conditions; this somewhat illogical behaviour can be recovered by setting the option CONTINUE_ON_ERROR. Fatal errors found in non-interactive shells include: • Failure to parse shell options passed when invoking the shell • Failure to change options with the set builtin • Parse errors of all sorts, including failures to parse mathematical expressions • Failures to set or modify variable behaviour with typeset, local, declare, export, integer, float • Execution of incorrectly positioned loop control structures (continue, break) • Attempts to use regular expression with no regular expression module available • Disallowed operations when the RESTRICTED options is set • Failure to create a pipe needed for a pipeline • Failure to create a multio • Failure to autoload a module needed for a declared shell feature • Errors creating command or process substitutions • Syntax errors in glob qualifiers • File generation errors where not caught by the option BAD_PATTERN • All bad patterns used for matching within case statements • File generation failures where not caused by NO_MATCH or similar options • All file generation errors where the pattern was used to create a multio • Memory errors where detected by the shell • Invalid subscripts to shell variables • Attempts to assign read-only variables • Logical errors with variables such as assignment to the wrong type • Use of invalid variable names • Errors in variable substitution syntax • Failure to convert characters in $'...' expressions If the POSIX_BUILTINS option is set, more errors associated with shell builtin commands are treated as fatal, as specified by the POSIX standard.  File: zsh.info, Node: Comments, Next: Aliasing, Prev: Errors, Up: Shell Grammar 6.7 Comments ============ In non-interactive shells, or in interactive shells with the INTERACTIVE_COMMENTS option set, a word beginning with the third character of the histchars parameter ('#' by default) causes that word and all the following characters up to a newline to be ignored.  File: zsh.info, Node: Aliasing, Next: Quoting, Prev: Comments, Up: Shell Grammar 6.8 Aliasing ============ Every eligible _word_ in the shell input is checked to see if there is an alias defined for it. If so, it is replaced by the text of the alias if it is in command position (if it could be the first word of a simple command), or if the alias is global. If the replacement text ends with a space, the next word in the shell input is always eligible for purposes of alias expansion. It is an error for the function name, WORD, in the sh-compatible function definition syntax 'WORD () ...' to be a word that resulted from alias expansion, unless the ALIAS_FUNC_DEF option is set. An alias is defined using the alias builtin; global aliases may be defined using the -g option to that builtin. A _word_ is defined as: • Any plain string or glob pattern • Any quoted string, using any quoting method (note that the quotes must be part of the alias definition for this to be eligible) • Any parameter reference or command substitution • Any series of the foregoing, concatenated without whitespace or other tokens between them • Any reserved word (case, do, else, etc.) • With global aliasing, any command separator, any redirection operator, and '(' or ')' when not part of a glob pattern Alias expansion is done on the shell input before any other expansion except history expansion. Therefore, if an alias is defined for the word foo, alias expansion may be avoided by quoting part of the word, e.g. \foo. Any form of quoting works, although there is nothing to prevent an alias being defined for the quoted form such as \foo as well. In particular, note that quoting must be used when using unalias to remove global aliases: % alias -g foo=bar % unalias foo unalias: no such hash table element: bar % unalias \foo % When POSIX_ALIASES is set, only plain unquoted strings are eligible for aliasing. The alias builtin does not reject ineligible aliases, but they are not expanded. For use with completion, which would remove an initial backslash followed by a character that isn't special, it may be more convenient to quote the word by starting with a single quote, i.e. 'foo; completion will automatically add the trailing single quote. 6.8.1 Alias difficulties ------------------------ Although aliases can be used in ways that bend normal shell syntax, not every string of non-white-space characters can be used as an alias. Any set of characters not listed as a word above is not a word, hence no attempt is made to expand it as an alias, no matter how it is defined (i.e. via the builtin or the special parameter aliases described in *note The zsh/parameter Module::). However, as noted in the case of POSIX_ALIASES above, the shell does not attempt to deduce whether the string corresponds to a word at the time the alias is created. For example, an expression containing an = at the start of a command line is an assignment and cannot be expanded as an alias; a lone = is not an assignment but can only be set as an alias using the parameter, as otherwise the = is taken part of the syntax of the builtin command. It is not presently possible to alias the '((' token that introduces arithmetic expressions, because until a full statement has been parsed, it cannot be distinguished from two consecutive '(' tokens introducing nested subshells. Also, if a separator such as && is aliased, \&& turns into the two tokens \& and &, each of which may have been aliased separately. Similarly for \<<, \>|, etc. There is a commonly encountered problem with aliases illustrated by the following code: alias echobar='echo bar'; echobar This prints a message that the command echobar could not be found. This happens because aliases are expanded when the code is read in; the entire line is read in one go, so that when echobar is executed it is too late to expand the newly defined alias. This is often a problem in shell scripts, functions, and code executed with 'source' or '.'. Consequently, use of functions rather than aliases is recommended in non-interactive code.  File: zsh.info, Node: Quoting, Prev: Aliasing, Up: Shell Grammar 6.9 Quoting =========== A character may be _quoted_ (that is, made to stand for itself) by preceding it with a '\'. '\' followed by a newline is ignored. A string enclosed between '$'' and ''' is processed the same way as the string arguments of the print builtin, and the resulting string is considered to be entirely quoted. A literal ''' character can be included in the string by using the '\'' escape. All characters enclosed between a pair of single quotes ('') that is not preceded by a '$' are quoted. A single quote cannot appear within single quotes unless the option RC_QUOTES is set, in which case a pair of single quotes are turned into a single quote. For example, print '''' outputs nothing apart from a newline if RC_QUOTES is not set, but one single quote if it is set. Inside double quotes (""), parameter and command substitution occur, and '\' quotes the characters '\', '`', '"', '$', and the first character of $histchars (default '!').  File: zsh.info, Node: Redirection, Next: Command Execution, Prev: Shell Grammar, Up: Top 7 Redirection ************* If a command is followed by & and job control is not active, then the default standard input for the command is the empty file /dev/null. Otherwise, the environment for the execution of a command contains the file descriptors of the invoking shell as modified by input/output specifications. The following may appear anywhere in a simple command or may precede or follow a complex command. Expansion occurs before WORD or DIGIT is used except as noted below. If the result of substitution on WORD produces more than one filename, redirection occurs for each separate filename in turn. < WORD Open file WORD for reading as standard input. It is an error to open a file in this fashion if it does not exist. <> WORD Open file WORD for reading and writing as standard input. If the file does not exist then it is created. > WORD Open file WORD for writing as standard output. If the file does not exist then it is created. If the file exists, and the CLOBBER option is unset, this causes an error; otherwise, it is truncated to zero length. >| WORD >! WORD Same as >, except that the file is truncated to zero length if it exists, regardless of CLOBBER. >> WORD Open file WORD for writing in append mode as standard output. If the file does not exist, and the CLOBBER and APPEND_CREATE options are both unset, this causes an error; otherwise, the file is created. >>| WORD >>! WORD Same as >>, except that the file is created if it does not exist, regardless of CLOBBER and APPEND_CREATE. <<[-] WORD The shell input is read up to a line that is the same as WORD, or to an end-of-file. No parameter expansion, command substitution or filename generation is performed on WORD. The resulting document, called a _here-document_, becomes the standard input. If any character of WORD is quoted with single or double quotes or a '\', no interpretation is placed upon the characters of the document. Otherwise, parameter and command substitution occurs, '\' followed by a newline is removed, and '\' must be used to quote the characters '\', '$', '`' and the first character of WORD. Note that WORD itself does not undergo shell expansion. Backquotes in WORD do not have their usual effect; instead they behave similarly to double quotes, except that the backquotes themselves are passed through unchanged. (This information is given for completeness and it is not recommended that backquotes be used.) Quotes in the form $'...' have their standard effect of expanding backslashed references to special characters. If <<- is used, then all leading tabs are stripped from WORD and from the document. <<< WORD Perform shell expansion on WORD and pass the result to standard input. This is known as a _here-string_. Compare the use of WORD in here-documents above, where WORD does not undergo shell expansion. The result will have a trailing newline after it. <& NUMBER >& NUMBER The standard input/output is duplicated from file descriptor NUMBER (see dup2(2)). <& - >& - Close the standard input/output. <& p >& p The input/output from/to the coprocess is moved to the standard input/output. >& WORD &> WORD (Except where '>& WORD' matches one of the above syntaxes; '&>' can always be used to avoid this ambiguity.) Redirects both standard output and standard error (file descriptor 2) in the manner of '> WORD'. Note that this does _not_ have the same effect as '> WORD 2>&1' in the presence of multios (see the section below). >&| WORD >&! WORD &>| WORD &>! WORD Redirects both standard output and standard error (file descriptor 2) in the manner of '>| WORD'. >>& WORD &>> WORD Redirects both standard output and standard error (file descriptor 2) in the manner of '>> WORD'. >>&| WORD >>&! WORD &>>| WORD &>>! WORD Redirects both standard output and standard error (file descriptor 2) in the manner of '>>| WORD'. If one of the above is preceded by a digit, then the file descriptor referred to is that specified by the digit instead of the default 0 or 1. The order in which redirections are specified is significant. The shell evaluates each redirection in terms of the (_file descriptor_, _file_) association at the time of evaluation. For example: ... 1>FNAME 2>&1 first associates file descriptor 1 with file FNAME. It then associates file descriptor 2 with the file associated with file descriptor 1 (that is, FNAME). If the order of redirections were reversed, file descriptor 2 would be associated with the terminal (assuming file descriptor 1 had been) and then file descriptor 1 would be associated with file FNAME. The '|&' command separator described in *note Simple Commands & Pipelines:: is a shorthand for '2>&1 |'. The various forms of process substitution, '<(LIST)', and '=(LIST)' for input and '>(LIST)' for output, are often used together with redirection. For example, if WORD in an output redirection is of the form '>(LIST)' then the output is piped to the command represented by LIST. See *note Process Substitution::. 7.1 Opening file descriptors using parameters ============================================= When the shell is parsing arguments to a command, and the shell option IGNORE_BRACES is not set, a different form of redirection is allowed: instead of a digit before the operator there is a valid shell identifier enclosed in braces. The shell will open a new file descriptor that is guaranteed to be at least 10 and set the parameter named by the identifier to the file descriptor opened. No whitespace is allowed between the closing brace and the redirection character. For example: ... {myfd}>&1 This opens a new file descriptor that is a duplicate of file descriptor 1 and sets the parameter myfd to the number of the file descriptor, which will be at least 10. The new file descriptor can be written to using the syntax >&$myfd. The file descriptor remains open in subshells and forked external executables. The syntax {VARID}>&-, for example {myfd}>&-, may be used to close a file descriptor opened in this fashion. Note that the parameter given by VARID must previously be set to a file descriptor in this case. It is an error to open or close a file descriptor in this fashion when the parameter is readonly. However, it is not an error to read or write a file descriptor using <&$PARAM or >&$PARAM if PARAM is readonly. If the option CLOBBER is unset, it is an error to open a file descriptor using a parameter that is already set to an open file descriptor previously allocated by this mechanism. Unsetting the parameter before using it for allocating a file descriptor avoids the error. Note that this mechanism merely allocates or closes a file descriptor; it does not perform any redirections from or to it. It is usually convenient to allocate a file descriptor prior to use as an argument to exec. The syntax does not in any case work when used around complex commands such as parenthesised subshells or loops, where the opening brace is interpreted as part of a command list to be executed in the current shell. The following shows a typical sequence of allocation, use, and closing of a file descriptor: integer myfd exec {myfd}>~/logs/mylogfile.txt print This is a log message. >&$myfd exec {myfd}>&- Note that the expansion of the variable in the expression >&$myfd occurs at the point the redirection is opened. This is after the expansion of command arguments and after any redirections to the left on the command line have been processed. 7.2 Multios =========== If the user tries to open a file descriptor for writing more than once, the shell opens the file descriptor as a pipe to a process that copies its input to all the specified outputs, similar to ‘tee’, provided the MULTIOS option is set, as it is by default. Thus: date >foo >bar writes the date to two files, named 'foo' and 'bar'. Note that a pipe is an implicit redirection; thus date >foo | cat writes the date to the file 'foo', and also pipes it to cat. Note that the shell opens all the files to be used in the multio process immediately, not at the point they are about to be written. Note also that redirections are always expanded in order. This happens regardless of the setting of the MULTIOS option, but with the option in effect there are additional consequences. For example, the meaning of the expression >&1 will change after a previous redirection: date >&1 >output In the case above, the >&1 refers to the standard output at the start of the line; the result is similar to the tee command. However, consider: date >output >&1 As redirections are evaluated in order, when the >&1 is encountered the standard output is set to the file output and another copy of the output is therefore sent to that file. This is unlikely to be what is intended. If the MULTIOS option is set, the word after a redirection operator is also subjected to filename generation (globbing). Thus : > * will truncate all files in the current directory, assuming there's at least one. (Without the MULTIOS option, it would create an empty file called '*'.) Similarly, you can do echo exit 0 >> *.sh If the user tries to open a file descriptor for reading more than once, the shell opens the file descriptor as a pipe to a process that copies all the specified inputs to its output in the order specified, provided the MULTIOS option is set. It should be noted that each file is opened immediately, not at the point where it is about to be read: this behaviour differs from cat, so if strictly standard behaviour is needed, cat should be used instead. Thus sort &$myfd. Note that a pipe is an implicit redirection; thus cat bar | sort bar > baz when MULTIOS is unset will truncate 'bar', and write 'Hello' into 'baz'. There is a problem when an output multio is attached to an external program. A simple example shows this: cat file >file1 >file2 cat file1 file2 Here, it is possible that the second 'cat' will not display the full contents of file1 and file2 (i.e. the original contents of file repeated twice). The reason for this is that the multios are spawned after the cat process is forked from the parent shell, so the parent shell does not wait for the multios to finish writing data. This means the command as shown can exit before file1 and file2 are completely written. As a workaround, it is possible to run the cat process as part of a job in the current shell: { cat file } >file >file2 Here, the {...} job will pause to wait for both files to be written. 7.3 Redirections with no command ================================ When a simple command consists of one or more redirection operators and zero or more parameter assignments, but no command name, zsh can behave in several ways. If the parameter NULLCMD is not set or the option CSH_NULLCMD is set, an error is caused. This is the ‘csh’ behavior and CSH_NULLCMD is set by default when emulating ‘csh’. If the option SH_NULLCMD is set, the builtin ':' is inserted as a command with the given redirections. This is the default when emulating ‘sh’ or ‘ksh’. Otherwise, if the parameter NULLCMD is set, its value will be used as a command with the given redirections. If both NULLCMD and READNULLCMD are set, then the value of the latter will be used instead of that of the former when the redirection is an input. The default for NULLCMD is 'cat' and for READNULLCMD is 'more'. Thus < file shows the contents of file on standard output, with paging if that is a terminal. NULLCMD and READNULLCMD may refer to shell functions.  File: zsh.info, Node: Command Execution, Next: Functions, Prev: Redirection, Up: Top 8 Command Execution ******************* If a command name contains no slashes, the shell attempts to locate it. If there exists a shell function by that name, the function is invoked as described in *note Functions::. If there exists a shell builtin by that name, the builtin is invoked. Otherwise, the shell searches each element of $path for a directory containing an executable file by that name. If execution fails: an error message is printed, and one of the following values is returned. 127 The search was unsuccessful. The error message is 'command not found: CMD'. 126 The executable file has insufficient permissions, is a directory or special file, or is not a script and is in a format unrecognized by the operating system. The exact conditions and error message are operating system-dependent; see execve(2). If execution fails because the file is not in executable format, and the file is not a directory, it is assumed to be a shell script. /bin/sh is spawned to execute it. If the program is a file beginning with '#!', the remainder of the first line specifies an interpreter for the program. The shell will execute the specified interpreter on operating systems that do not handle this executable format in the kernel. If no external command is found but a function command_not_found_handler exists the shell executes this function with all command line arguments. The return status of the function becomes the status of the command. Note that the handler is executed in a subshell forked to execute an external command, hence changes to directories, shell parameters, etc. have no effect on the main shell.  File: zsh.info, Node: Functions, Next: Jobs & Signals, Prev: Command Execution, Up: Top 9 Functions *********** Shell functions are defined with the function reserved word or the special syntax 'FUNCNAME ()'. Shell functions are read in and stored internally. Alias names are resolved when the function is read. Functions are executed like commands with the arguments passed as positional parameters. (See *note Command Execution::.) Functions execute in the same process as the caller and share all files and present working directory with the caller. A trap on EXIT set inside a function is executed after the function completes in the environment of the caller. The return builtin is used to return from function calls. Function identifiers can be listed with the functions builtin. Functions can be undefined with the unfunction builtin. 9.1 Autoloading Functions ========================= A function can be marked as _undefined_ using the autoload builtin (or 'functions -u' or 'typeset -fu'). Such a function has no body. When the function is first executed, the shell searches for its definition using the elements of the fpath variable. Thus to define functions for autoloading, a typical sequence is: fpath=(~/myfuncs $fpath) autoload myfunc1 myfunc2 ... The usual alias expansion during reading will be suppressed if the autoload builtin or its equivalent is given the option -U. This is recommended for the use of functions supplied with the zsh distribution. Note that for functions precompiled with the zcompile builtin command the flag -U must be provided when the .zwc file is created, as the corresponding information is compiled into the latter. For each ELEMENT in fpath, the shell looks for three possible files, the newest of which is used to load the definition for the function: ELEMENT.zwc A file created with the zcompile builtin command, which is expected to contain the definitions for all functions in the directory named ELEMENT. The file is treated in the same manner as a directory containing files for functions and is searched for the definition of the function. If the definition is not found, the search for a definition proceeds with the other two possibilities described below. If ELEMENT already includes a .zwc extension (i.e. the extension was explicitly given by the user), ELEMENT is searched for the definition of the function without comparing its age to that of other files; in fact, there does not need to be any directory named ELEMENT without the suffix. Thus including an element such as '/usr/local/funcs.zwc' in fpath will speed up the search for functions, with the disadvantage that functions included must be explicitly recompiled by hand before the shell notices any changes. ELEMENT/FUNCTION.zwc A file created with zcompile, which is expected to contain the definition for FUNCTION. It may include other function definitions as well, but those are neither loaded nor executed; a file found in this way is searched _only_ for the definition of FUNCTION. ELEMENT/FUNCTION A file of zsh command text, taken to be the definition for FUNCTION. In summary, the order of searching is, first, in the _parents of_ directories in fpath for the newer of either a compiled directory or a directory in fpath; second, if more than one of these contains a definition for the function that is sought, the leftmost in the fpath is chosen; and third, within a directory, the newer of either a compiled function or an ordinary function definition is used. If the KSH_AUTOLOAD option is set, or the file contains only a simple definition of the function, the file's contents will be executed. This will normally define the function in question, but may also perform initialization, which is executed in the context of the function execution, and may therefore define local parameters. It is an error if the function is not defined by loading the file. Otherwise, the function body (with no surrounding 'FUNCNAME() {...}') is taken to be the complete contents of the file. This form allows the file to be used directly as an executable shell script. If processing of the file results in the function being re-defined, the function itself is not re-executed. To force the shell to perform initialization and then call the function defined, the file should contain initialization code (which will be executed then discarded) in addition to a complete function definition (which will be retained for subsequent calls to the function), and a call to the shell function, including any arguments, at the end. For example, suppose the autoload file func contains func() { print This is func; } print func is initialized then 'func; func' with KSH_AUTOLOAD set will produce both messages on the first call, but only the message 'This is func' on the second and subsequent calls. Without KSH_AUTOLOAD set, it will produce the initialization message on the first call, and the other message on the second and subsequent calls. It is also possible to create a function that is not marked as autoloaded, but which loads its own definition by searching fpath, by using 'autoload -X' within a shell function. For example, the following are equivalent: myfunc() { autoload -X } myfunc args... and unfunction myfunc # if myfunc was defined autoload myfunc myfunc args... In fact, the functions command outputs 'builtin autoload -X' as the body of an autoloaded function. This is done so that eval "$(functions)" produces a reasonable result. A true autoloaded function can be identified by the presence of the comment '# undefined' in the body, because all comments are discarded from defined functions. To load the definition of an autoloaded function myfunc without executing myfunc, use: autoload +X myfunc 9.2 Anonymous Functions ======================= If no name is given for a function, it is 'anonymous' and is handled specially. Either form of function definition may be used: a '()' with no preceding name, or a 'function' with an immediately following open brace. The function is executed immediately at the point of definition and is not stored for future use. The function name is set to '(anon)'. Arguments to the function may be specified as words following the closing brace defining the function, hence if there are none no arguments (other than $0) are set. This is a difference from the way other functions are parsed: normal function definitions may be followed by certain keywords such as 'else' or 'fi', which will be treated as arguments to anonymous functions, so that a newline or semicolon is needed to force keyword interpretation. Note also that the argument list of any enclosing script or function is hidden (as would be the case for any other function called at this point). Redirections may be applied to the anonymous function in the same manner as to a current-shell structure enclosed in braces. The main use of anonymous functions is to provide a scope for local variables. This is particularly convenient in start-up files as these do not provide their own local variable scope. For example, variable=outside function { local variable=inside print "I am $variable with arguments $*" } this and that print "I am $variable" outputs the following: I am inside with arguments this and that I am outside Note that function definitions with arguments that expand to nothing, for example 'name=; function $name { ... }', are not treated as anonymous functions. Instead, they are treated as normal function definitions where the definition is silently discarded. 9.3 Special Functions ===================== Certain functions, if defined, have special meaning to the shell. 9.3.1 Hook Functions -------------------- For the functions below, it is possible to define an array that has the same name as the function with '_functions' appended. Any element in such an array is taken as the name of a function to execute; it is executed in the same context and with the same arguments and same initial value of $? as the basic function. For example, if $chpwd_functions is an array containing the values 'mychpwd', 'chpwd_save_dirstack', then the shell attempts to execute the functions 'chpwd', 'mychpwd' and 'chpwd_save_dirstack', in that order. Any function that does not exist is silently ignored. A function found by this mechanism is referred to elsewhere as a _hook function_. An error in any function causes subsequent functions not to be run. Note further that an error in a precmd hook causes an immediately following periodic function not to run (though it may run at the next opportunity). chpwd Executed whenever the current working directory is changed. periodic If the parameter PERIOD is set, this function is executed every $PERIOD seconds, just before a prompt. Note that if multiple functions are defined using the array periodic_functions only one period is applied to the complete set of functions, and the scheduled time is not reset if the list of functions is altered. Hence the set of functions is always called together. precmd Executed before each prompt. Note that precommand functions are not re-executed simply because the command line is redrawn, as happens, for example, when a notification about an exiting job is displayed. preexec Executed just after a command has been read and is about to be executed. If the history mechanism is active (regardless of whether the line was discarded from the history buffer), the string that the user typed is passed as the first argument, otherwise it is an empty string. The actual command that will be executed (including expanded aliases) is passed in two different forms: the second argument is a single-line, size-limited version of the command (with things like function bodies elided); the third argument contains the full text that is being executed. zshaddhistory Executed when a history line has been read interactively, but before it is executed. The sole argument is the complete history line (so that any terminating newline will still be present). If any of the hook functions returns status 1 (or any non-zero value other than 2, though this is not guaranteed for future versions of the shell) the history line will not be saved, although it lingers in the history until the next line is executed, allowing you to reuse or edit it immediately. If any of the hook functions returns status 2 the history line will be saved on the internal history list, but not written to the history file. In case of a conflict, the first non-zero status value is taken. A hook function may call 'fc -p ...' to switch the history context so that the history is saved in a different file from that in the global HISTFILE parameter. This is handled specially: the history context is automatically restored after the processing of the history line is finished. The following example function works with one of the options INC_APPEND_HISTORY or SHARE_HISTORY set, in order that the line is written out immediately after the history entry is added. It first adds the history line to the normal history with the newline stripped, which is usually the correct behaviour. Then it switches the history context so that the line will be written to a history file in the current directory. zshaddhistory() { print -sr -- ${1%%$'\n'} fc -p .zsh_local_history } zshexit Executed at the point where the main shell is about to exit normally. This is not called by exiting subshells, nor when the exec precommand modifier is used before an external command. Also, unlike TRAPEXIT, it is not called when functions exit. 9.3.2 Trap Functions -------------------- The functions below are treated specially but do not have corresponding hook arrays. TRAPNAL If defined and non-null, this function will be executed whenever the shell catches a signal SIGNAL, where NAL is a signal name as specified for the kill builtin. The signal number will be passed as the first parameter to the function. If a function of this form is defined and null, the shell and processes spawned by it will ignore SIGNAL. The return status from the function is handled specially. If it is zero, the signal is assumed to have been handled, and execution continues normally. Otherwise, the shell will behave as interrupted except that the return status of the trap is retained. Programs terminated by uncaught signals typically return the status 128 plus the signal number. Hence the following causes the handler for SIGINT to print a message, then mimic the usual effect of the signal. TRAPINT() { print "Caught SIGINT, aborting." return $(( 128 + $1 )) } The functions TRAPZERR, TRAPDEBUG and TRAPEXIT are never executed inside other traps. TRAPDEBUG If the option DEBUG_BEFORE_CMD is set (as it is by default), executed before each command; otherwise executed after each command. See the description of the trap builtin in *note Shell Builtin Commands:: for details of additional features provided in debug traps. TRAPEXIT Executed when the shell exits, or when the current function exits if defined inside a function. The value of $? at the start of execution is the exit status of the shell or the return status of the function exiting. TRAPZERR Executed whenever a command has a non-zero exit status. However, the function is not executed if the command occurred in a sublist followed by '&&' or '||'; only the final command in a sublist of this type causes the trap to be executed. The function TRAPERR acts the same as TRAPZERR on systems where there is no SIGERR (this is the usual case). The functions beginning 'TRAP' may alternatively be defined with the trap builtin: this may be preferable for some uses. Setting a trap with one form removes any trap of the other form for the same signal; removing a trap in either form removes all traps for the same signal. The forms TRAPNAL() { # code } ('function traps') and trap ' # code ' NAL ('list traps') are equivalent in most ways, the exceptions being the following: • Function traps have all the properties of normal functions, appearing in the list of functions and being called with their own function context rather than the context where the trap was triggered. • The return status from function traps is special, whereas a return from a list trap causes the surrounding context to return with the given status. • Function traps are not reset within subshells, in accordance with zsh behaviour; list traps are reset, in accordance with POSIX behaviour.  File: zsh.info, Node: Jobs & Signals, Next: Arithmetic Evaluation, Prev: Functions, Up: Top 10 Jobs & Signals ***************** 10.1 Jobs ========= If the MONITOR option is set, an interactive shell associates a _job_ with each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them small integer numbers. When a job is started asynchronously with '&', the shell prints a line to standard error which looks like: [1] 1234 indicating that the job which was started asynchronously was job number 1 and had one (top-level) process, whose process ID was 1234. If a job is started with '&|' or '&!', then that job is immediately disowned. After startup, it does not have a place in the job table, and is not subject to the job control features described here. If you are running a job and wish to do something else you may hit the key ^Z (control-Z) which sends a TSTP signal to the current job: this key may be redefined by the susp option of the external stty command. The shell will then normally indicate that the job has been 'suspended', and print another prompt. You can then manipulate the state of this job, putting it in the background with the bg command, or run some other commands and then eventually bring the job back into the foreground with the foreground command fg. A ^Z takes effect immediately and is like an interrupt in that pending output and unread input are discarded when it is typed. A job being run in the background will suspend if it tries to read from the terminal. Note that if the job running in the foreground is a shell function, then suspending it will have the effect of causing the shell to fork. This is necessary to separate the function's state from that of the parent shell performing the job control, so that the latter can return to the command line prompt. As a result, even if fg is used to continue the job the function will no longer be part of the parent shell, and any variables set by the function will not be visible in the parent shell. Thus the behaviour is different from the case where the function was never suspended. Zsh is different from many other shells in this regard. One additional side effect is that use of disown with a job created by suspending shell code in this fashion is delayed: the job can only be disowned once any process started from the parent shell has terminated. At that point, the disowned job disappears silently from the job list. The same behaviour is found when the shell is executing code as the right hand side of a pipeline or any complex shell construct such as if, for, etc., in order that the entire block of code can be managed as a single job. Background jobs are normally allowed to produce output, but this can be disabled by giving the command 'stty tostop'. If you set this tty option, then background jobs will suspend when they try to produce output like they do when they try to read input. When a command is suspended and continued later with the fg or wait builtins, zsh restores tty modes that were in effect when it was suspended. This (intentionally) does not apply if the command is continued via 'kill -CONT', nor when it is continued with bg. There are several ways to refer to jobs in the shell. A job can be referred to by the process ID of any process of the job or by one of the following: %NUMBER The job with the given number. %STRING The last job whose command line begins with STRING. %?STRING The last job whose command line contains STRING. %% Current job. %+ Equivalent to '%%'. %- Previous job. The shell learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible. If the NOTIFY option is not set, it waits until just before it prints a prompt before it informs you. All such notifications are sent directly to the terminal, not to the standard output or standard error. When the monitor mode is on, each background job that completes triggers any trap set for CHLD. When you try to leave the shell while jobs are running or suspended, you will be warned that 'You have suspended (running) jobs'. You may use the jobs command to see what they are. If you do this or immediately try to exit again, the shell will not warn you a second time; the suspended jobs will be terminated, and the running jobs will be sent a SIGHUP signal, if the HUP option is set. To avoid having the shell terminate the running jobs, either use the nohup(1) command or the disown builtin. 10.2 Signals ============ The INT and QUIT signals for an invoked command are ignored if the command is followed by '&' and the MONITOR option is not active. The shell itself always ignores the QUIT signal. Otherwise, signals have the values inherited by the shell from its parent (but see the TRAPNAL special functions in *note Functions::). Certain jobs are run asynchronously by the shell other than those explicitly put into the background; even in cases where the shell would usually wait for such jobs, an explicit exit command or exit due to the option ERR_EXIT will cause the shell to exit without waiting. Examples of such asynchronous jobs are process substitution, see *note Process Substitution::, and the handler processes for multios, see the section _Multios_ in *note Redirection::.  File: zsh.info, Node: Arithmetic Evaluation, Next: Conditional Expressions, Prev: Jobs & Signals, Up: Top 11 Arithmetic Evaluation ************************ The shell can perform integer and floating point arithmetic, either using the builtin let, or via a substitution of the form $((...)). For integers, the shell is usually compiled to use 8-byte precision where this is available, otherwise precision is 4 bytes. This can be tested, for example, by giving the command 'print - $(( 12345678901 ))'; if the number appears unchanged, the precision is at least 8 bytes. Floating point arithmetic always uses the 'double' type with whatever corresponding precision is provided by the compiler and the library. The let builtin command takes arithmetic expressions as arguments; each is evaluated separately. Since many of the arithmetic operators, as well as spaces, require quoting, an alternative form is provided: for any command which begins with a '((', all the characters until a matching '))' are treated as a double-quoted expression and arithmetic expansion performed as for an argument of let. More precisely, '((...))' is equivalent to 'let "..."'. The return status is 0 if the arithmetic value of the expression is non-zero, 1 if it is zero, and 2 if an error occurred. For example, the following statement (( val = 2 + 1 )) is equivalent to let "val = 2 + 1" both assigning the value 3 to the shell variable val and returning a zero status. Integers can be in bases other than 10. A leading '0x' or '0X' denotes hexadecimal and a leading '0b' or '0B' binary. Integers may also be of the form 'BASE#N', where BASE is a decimal number between two and thirty-six representing the arithmetic base and N is a number in that base (for example, '16#ff' is 255 in hexadecimal). The BASE# may also be omitted, in which case base 10 is used. For backwards compatibility the form '[BASE]N' is also accepted. An integer expression or a base given in the form 'BASE#N' may contain underscores ('_') after the leading digit for visual guidance; these are ignored in computation. Examples are 1_000_000 or 0xffff_ffff which are equivalent to 1000000 and 0xffffffff respectively. It is also possible to specify a base to be used for output in the form '[#BASE]', for example '[#16]'. This is used when outputting arithmetical substitutions or when assigning to scalar parameters, but an explicitly defined integer or floating point parameter will not be affected. If an integer variable is implicitly defined by an arithmetic expression, any base specified in this way will be set as the variable's output arithmetic base as if the option '-i BASE' to the typeset builtin had been used. The expression has no precedence and if it occurs more than once in a mathematical expression, the last encountered is used. For clarity it is recommended that it appear at the beginning of an expression. As an example: typeset -i 16 y print $(( [#8] x = 32, y = 32 )) print $x $y outputs first '8#40', the rightmost value in the given output base, and then '8#40 16#20', because y has been explicitly declared to have output base 16, while x (assuming it does not already exist) is implicitly typed by the arithmetic evaluation, where it acquires the output base 8. The BASE may be replaced or followed by an underscore, which may itself be followed by a positive integer (if it is missing the value 3 is used). This indicates that underscores should be inserted into the output string, grouping the number for visual clarity. The following integer specifies the number of digits to group together. For example: setopt cbases print $(( [#16_4] 65536 ** 2 )) outputs '0x1_0000_0000'. The feature can be used with floating point numbers, in which case the base must be omitted; grouping is away from the decimal point. For example, zmodload zsh/mathfunc print $(( [#_] sqrt(1e7) )) outputs '3_162.277_660_168_379_5' (the number of decimal places shown may vary). If the C_BASES option is set, hexadecimal numbers are output in the standard C format, for example '0xFF' instead of the usual '16#FF'. If the option OCTAL_ZEROES is also set (it is not by default), octal numbers will be treated similarly and hence appear as '077' instead of '8#77'. This option has no effect on the output of bases other than hexadecimal and octal, and these formats are always understood on input. When an output base is specified using the '[#BASE]' syntax, an appropriate base prefix will be output if necessary, so that the value output is valid syntax for input. If the # is doubled, for example '[##16]', then no base prefix is output. Floating point constants are recognized by the presence of a decimal point or an exponent. The decimal point may be the first character of the constant, but the exponent character e or E may not, as it will be taken for a parameter name. All numeric parts (before and after the decimal point and in the exponent) may contain underscores after the leading digit for visual guidance; these are ignored in computation. An arithmetic expression uses nearly the same syntax and associativity of expressions as in C. In the native mode of operation, the following operators are supported (listed in decreasing order of precedence): + - ! ~ ++ -- unary plus/minus, logical NOT, complement, {pre,post}{in,de}crement << >> bitwise shift left, right & bitwise AND ^ bitwise XOR | bitwise OR ** exponentiation * / % multiplication, division, modulus (remainder) + - addition, subtraction < > <= >= comparison == != equality and inequality && logical AND || ^^ logical OR, XOR ? : ternary operator = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **= assignment , comma operator The operators '&&', '||', '&&=', and '||=' are short-circuiting, and only one of the latter two expressions in a ternary operator is evaluated. Note the precedence of the bitwise AND, OR, and XOR operators. With the option C_PRECEDENCES the precedences (but no other properties) of the operators are altered to be the same as those in most other languages that support the relevant operators: + - ! ~ ++ -- unary plus/minus, logical NOT, complement, {pre,post}{in,de}crement ** exponentiation * / % multiplication, division, modulus (remainder) + - addition, subtraction << >> bitwise shift left, right < > <= >= comparison == != equality and inequality & bitwise AND ^ bitwise XOR | bitwise OR && logical AND ^^ logical XOR || logical OR ? : ternary operator = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **= assignment , comma operator Note the precedence of exponentiation in both cases is below that of unary operators, hence '-3**2' evaluates as '9', not '-9'. Use parentheses where necessary: '-(3**2)'. This is for compatibility with other shells. Mathematical functions can be called with the syntax 'FUNC(ARGS)', where the function decides if the ARGS is used as a string or a comma-separated list of arithmetic expressions. The shell currently defines no mathematical functions by default, but the module zsh/mathfunc may be loaded with the zmodload builtin to provide standard floating point mathematical functions. An expression of the form '##X' where X is any character sequence such as 'a', '^A', or '\M-\C-x' gives the value of this character and an expression of the form '#NAME' gives the value of the first character of the contents of the parameter NAME. Character values are according to the character set used in the current locale; for multibyte character handling the option MULTIBYTE must be set. Note that this form is different from '$#NAME', a standard parameter substitution which gives the length of the parameter NAME. '#\' is accepted instead of '##', but its use is deprecated. Named parameters and subscripted arrays can be referenced by name within an arithmetic expression without using the parameter expansion syntax. For example, ((val2 = val1 * 2)) assigns twice the value of $val1 to the parameter named val2. An internal integer representation of a named parameter can be specified with the integer builtin. Arithmetic evaluation is performed on the value of each assignment to a named parameter declared integer in this manner. Assigning a floating point number to an integer results in rounding towards zero. Likewise, floating point numbers can be declared with the float builtin; there are two types, differing only in their output format, as described for the typeset builtin. The output format can be bypassed by using arithmetic substitution instead of the parameter substitution, i.e. '${FLOAT}' uses the defined format, but '$((FLOAT))' uses a generic floating point format. Promotion of integer to floating point values is performed where necessary. In addition, if any operator which requires an integer ('&', '|', '^', '<<', '>>' and their equivalents with assignment) is given a floating point argument, it will be silently rounded towards zero except for '~' which rounds down. Users should beware that, in common with many other programming languages but not software designed for calculation, the evaluation of an expression in zsh is taken a term at a time and promotion of integers to floating point does not occur in terms only containing integers. A typical result of this is that a division such as 6/8 is truncated, in this being rounded towards 0. The FORCE_FLOAT shell option can be used in scripts or functions where floating point evaluation is required throughout. Scalar variables can hold integer or floating point values at different times; there is no memory of the numeric type in this case. If a variable is first assigned in a numeric context without previously being declared, it will be implicitly typed as integer or float and retain that type either until the type is explicitly changed or until the end of the scope. This can have unforeseen consequences. For example, in the loop for (( f = 0; f < 1; f += 0.1 )); do # use $f done if f has not already been declared, the first assignment will cause it to be created as an integer, and consequently the operation 'f += 0.1' will always cause the result to be truncated to zero, so that the loop will fail. A simple fix would be to turn the initialization into 'f = 0.0'. It is therefore best to declare numeric variables with explicit types.  File: zsh.info, Node: Conditional Expressions, Next: Prompt Expansion, Prev: Arithmetic Evaluation, Up: Top 12 Conditional Expressions ************************** A _conditional expression_ is used with the [[ compound command to test attributes of files and to compare strings. Each expression can be constructed from one or more of the following unary or binary expressions: -a FILE true if FILE exists. -b FILE true if FILE exists and is a block special file. -c FILE true if FILE exists and is a character special file. -d FILE true if FILE exists and is a directory. -e FILE true if FILE exists. -f FILE true if FILE exists and is a regular file. -g FILE true if FILE exists and has its setgid bit set. -h FILE true if FILE exists and is a symbolic link. -k FILE true if FILE exists and has its sticky bit set. -n STRING true if length of STRING is non-zero. -o OPTION true if option named OPTION is on. OPTION may be a single character, in which case it is a single letter option name. (See *note Specifying Options::.) When no option named OPTION exists, and the POSIX_BUILTINS option hasn't been set, return 3 with a warning. If that option is set, return 1 with no warning. -p FILE true if FILE exists and is a FIFO special file (named pipe). -r FILE true if FILE exists and is readable by current process. -s FILE true if FILE exists and has size greater than zero. -t FD true if file descriptor number FD is open and associated with a terminal device. (note: FD is not optional) -u FILE true if FILE exists and has its setuid bit set. -v VARNAME true if shell variable VARNAME is set. -w FILE true if FILE exists and is writable by current process. -x FILE true if FILE exists and is executable by current process. If FILE exists and is a directory, then the current process has permission to search in the directory. -z STRING true if length of STRING is zero. -L FILE true if FILE exists and is a symbolic link. -O FILE true if FILE exists and is owned by the effective user ID of this process. -G FILE true if FILE exists and its group matches the effective group ID of this process. -S FILE true if FILE exists and is a socket. -N FILE true if FILE exists and its access time is not newer than its modification time. FILE1 -nt FILE2 true if FILE1 exists and is newer than FILE2. FILE1 -ot FILE2 true if FILE1 exists and is older than FILE2. FILE1 -ef FILE2 true if FILE1 and FILE2 exist and refer to the same file. STRING = PATTERN STRING == PATTERN true if STRING matches PATTERN. The two forms are exactly equivalent. The '=' form is the traditional shell syntax (and hence the only one generally used with the test and [ builtins); the '==' form provides compatibility with other sorts of computer language. STRING != PATTERN true if STRING does not match PATTERN. STRING =~ REGEXP true if STRING matches the regular expression REGEXP. If the option RE_MATCH_PCRE is set REGEXP is tested as a PCRE regular expression using the zsh/pcre module, else it is tested as a POSIX extended regular expression using the zsh/regex module. Upon successful match, some variables will be updated; no variables are changed if the matching fails. If the option BASH_REMATCH is not set the scalar parameter MATCH is set to the substring that matched the pattern and the integer parameters MBEGIN and MEND to the index of the start and end, respectively, of the match in STRING, such that if STRING is contained in variable var the expression '${var[$MBEGIN,$MEND]}' is identical to '$MATCH'. The setting of the option KSH_ARRAYS is respected. Likewise, the array match is set to the substrings that matched parenthesised subexpressions and the arrays mbegin and mend to the indices of the start and end positions, respectively, of the substrings within STRING. The arrays are not set if there were no parenthesised subexpressions. For example, if the string 'a short string' is matched against the regular expression 's(...)t', then (assuming the option KSH_ARRAYS is not set) MATCH, MBEGIN and MEND are 'short', 3 and 7, respectively, while match, mbegin and mend are single entry arrays containing the strings 'hor', '4' and '6', respectively. If the option BASH_REMATCH is set the array BASH_REMATCH is set to the substring that matched the pattern followed by the substrings that matched parenthesised subexpressions within the pattern. STRING1 < STRING2 true if STRING1 comes before STRING2 based on ASCII value of their characters. STRING1 > STRING2 true if STRING1 comes after STRING2 based on ASCII value of their characters. EXP1 -eq EXP2 true if EXP1 is numerically equal to EXP2. Note that for purely numeric comparisons use of the ((...)) builtin described in *note Arithmetic Evaluation:: is more convenient than conditional expressions. EXP1 -ne EXP2 true if EXP1 is numerically not equal to EXP2. EXP1 -lt EXP2 true if EXP1 is numerically less than EXP2. EXP1 -gt EXP2 true if EXP1 is numerically greater than EXP2. EXP1 -le EXP2 true if EXP1 is numerically less than or equal to EXP2. EXP1 -ge EXP2 true if EXP1 is numerically greater than or equal to EXP2. ( EXP ) true if EXP is true. ! EXP true if EXP is false. EXP1 && EXP2 true if EXP1 and EXP2 are both true. EXP1 || EXP2 true if either EXP1 or EXP2 is true. For compatibility, if there is a single argument that is not syntactically significant, typically a variable, the condition is treated as a test for whether the expression expands as a string of non-zero length. In other words, [[ $var ]] is the same as [[ -n $var ]]. It is recommended that the second, explicit, form be used where possible. Normal shell expansion is performed on the FILE, STRING and PATTERN arguments, but the result of each expansion is constrained to be a single word, similar to the effect of double quotes. Filename generation is not performed on any form of argument to conditions. However, it can be forced in any case where normal shell expansion is valid and when the option EXTENDED_GLOB is in effect by using an explicit glob qualifier of the form (#q) at the end of the string. A normal glob qualifier expression may appear between the 'q' and the closing parenthesis; if none appears the expression has no effect beyond causing filename generation. The results of filename generation are joined together to form a single word, as with the results of other forms of expansion. This special use of filename generation is only available with the [[ syntax. If the condition occurs within the [ or test builtin commands then globbing occurs instead as part of normal command line expansion before the condition is evaluated. In this case it may generate multiple words which are likely to confuse the syntax of the test command. For example, [[ -n file*(#qN) ]] produces status zero if and only if there is at least one file in the current directory beginning with the string 'file'. The globbing qualifier N ensures that the expression is empty if there is no matching file. Pattern metacharacters are active for the PATTERN arguments; the patterns are the same as those used for filename generation, see *note Filename Generation::, but there is no special behaviour of '/' nor initial dots, and no glob qualifiers are allowed. In each of the above expressions, if FILE is of the form '/dev/fd/N', where N is an integer, then the test applied to the open file whose descriptor number is N, even if the underlying system does not support the /dev/fd directory. In the forms which do numeric comparison, the expressions EXP undergo arithmetic expansion as if they were enclosed in $((...)). For example, the following: [[ ( -f foo || -f bar ) && $report = y* ]] && print File exists. tests if either file foo or file bar exists, and if so, if the value of the parameter report begins with 'y'; if the complete condition is true, the message 'File exists.' is printed.  File: zsh.info, Node: Prompt Expansion, Next: Expansion, Prev: Conditional Expressions, Up: Top 13 Prompt Expansion ******************* 13.1 Expansion of Prompt Sequences ================================== Prompt sequences undergo a special form of expansion. This type of expansion is also available using the -P option to the print builtin. If the PROMPT_SUBST option is set, the prompt string is first subjected to _parameter expansion_, _command substitution_ and _arithmetic expansion_. See *note Expansion::. Certain escape sequences may be recognised in the prompt string. If the PROMPT_BANG option is set, a '!' in the prompt is replaced by the current history event number. A literal '!' may then be represented as '!!'. If the PROMPT_PERCENT option is set, certain escape sequences that start with '%' are expanded. Many escapes are followed by a single character, although some of these take an optional integer argument that should appear between the '%' and the next character of the sequence. More complicated escape sequences are available to provide conditional expansion. 13.2 Simple Prompt Escapes ========================== 13.2.1 Special characters ------------------------- %% A '%'. %) A ')'. 13.2.2 Login information ------------------------ %l The line (tty) the user is logged in on, without '/dev/' prefix. If the name starts with '/dev/tty', that prefix is stripped. %M The full machine hostname. %m The hostname up to the first '.'. An integer may follow the '%' to specify how many components of the hostname are desired. With a negative integer, trailing components of the hostname are shown. %n $USERNAME. %y The line (tty) the user is logged in on, without '/dev/' prefix. This does not treat '/dev/tty' names specially. 13.2.3 Shell state ------------------ %# A '#' if the shell is running with privileges, a '%' if not. Equivalent to '%(!.#.%%)'. The definition of 'privileged', for these purposes, is that either the effective user ID is zero, or, if POSIX.1e capabilities are supported, that at least one capability is raised in either the Effective or Inheritable capability vectors. %? The return status of the last command executed just before the prompt. %_ The status of the parser, i.e. the shell constructs (like 'if' and 'for') that have been started on the command line. If given an integer number that many strings will be printed; zero or negative or no integer means print as many as there are. This is most useful in prompts PS2 for continuation lines and PS4 for debugging with the XTRACE option; in the latter case it will also work non-interactively. %^ The status of the parser in reverse. This is the same as '%_' other than the order of strings. It is often used in RPS2. %d %/ Current working directory. If an integer follows the '%', it specifies a number of trailing components of the current working directory to show; zero means the whole path. A negative integer specifies leading components, i.e. %-1d specifies the first component. %~ As %d and %/, but if the current working directory starts with $HOME, that part is replaced by a '~'. Furthermore, if it has a named directory as its prefix, that part is replaced by a '~' followed by the name of the directory, but only if the result is shorter than the full path; *note Filename Expansion::. %e Evaluation depth of the current sourced file, shell function, or eval. This is incremented or decremented every time the value of %N is set or reverted to a previous value, respectively. This is most useful for debugging as part of $PS4. %h %! Current history event number. %i The line number currently being executed in the script, sourced file, or shell function given by %N. This is most useful for debugging as part of $PS4. %I The line number currently being executed in the file %x. This is similar to %i, but the line number is always a line number in the file where the code was defined, even if the code is a shell function. %j The number of jobs. %L The current value of $SHLVL. %N The name of the script, sourced file, or shell function that zsh is currently executing, whichever was started most recently. If there is none, this is equivalent to the parameter $0. An integer may follow the '%' to specify a number of trailing path components to show; zero means the full path. A negative integer specifies leading components. %x The name of the file containing the source code currently being executed. This behaves as %N except that function and eval command names are not shown, instead the file where they were defined. %c %. %C Trailing component of the current working directory. An integer may follow the '%' to get more than one component. Unless '%C' is used, tilde contraction is performed first. These are deprecated as %c and %C are equivalent to %1~ and %1/, respectively, while explicit positive integers have the same effect as for the latter two sequences. 13.2.4 Date and time -------------------- %D The date in YY-MM-DD format. %T Current time of day, in 24-hour format. %t %@ Current time of day, in 12-hour, am/pm format. %* Current time of day in 24-hour format, with seconds. %w The date in DAY-DD format. %W The date in MM/DD/YY format. %D{STRING} STRING is formatted using the strftime function. See strftime(3) for more details. Various zsh extensions provide numbers with no leading zero or space if the number is a single digit: %f a day of the month %K the hour of the day on the 24-hour clock %L the hour of the day on the 12-hour clock In addition, if the system supports the POSIX gettimeofday system call, %. provides decimal fractions of a second since the epoch with leading zeroes. By default three decimal places are provided, but a number of digits up to 9 may be given following the %; hence %6. outputs microseconds, and %9. outputs nanoseconds. (The latter requires a nanosecond-precision clock_gettime; systems lacking this will return a value multiplied by the appropriate power of 10.) A typical example of this is the format '%D{%H:%M:%S.%.}'. The GNU extension %N is handled as a synonym for %9.. Additionally, the GNU extension that a '-' between the % and the format character causes a leading zero or space to be stripped is handled directly by the shell for the format characters d, f, H, k, l, m, M, S and y; any other format characters are provided to the system's strftime(3) with any leading '-' present, so the handling is system dependent. Further GNU (or other) extensions are also passed to strftime(3) and may work if the system supports them. 13.2.5 Visual effects --------------------- %B (%b) Start (stop) boldface mode. %E Clear to end of line. %U (%u) Start (stop) underline mode. %S (%s) Start (stop) standout mode. %F (%f) Start (stop) using a different foreground colour, if supported by the terminal. The colour may be specified two ways: either as a numeric argument, as normal, or by a sequence in braces following the %F, for example %F{red}. In the latter case the values allowed are as described for the fg zle_highlight attribute; *note Character Highlighting::. This means that numeric colours are allowed in the second format also. %K (%k) Start (stop) using a different bacKground colour. The syntax is identical to that for %F and %f. %{...%} Include a string as a literal escape sequence. The string within the braces should not change the cursor position. Brace pairs can nest. A positive numeric argument between the % and the { is treated as described for %G below. %G Within a %{...%} sequence, include a 'glitch': that is, assume that a single character width will be output. This is useful when outputting characters that otherwise cannot be correctly handled by the shell, such as the alternate character set on some terminals. The characters in question can be included within a %{...%} sequence together with the appropriate number of %G sequences to indicate the correct width. An integer between the '%' and 'G' indicates a character width other than one. Hence %{SEQ%2G%} outputs SEQ and assumes it takes up the width of two standard characters. Multiple uses of %G accumulate in the obvious fashion; the position of the %G is unimportant. Negative integers are not handled. Note that when prompt truncation is in use it is advisable to divide up output into single characters within each %{...%} group so that the correct truncation point can be found. 13.3 Conditional Substrings in Prompts ====================================== %v The value of the first element of the psvar array parameter. Following the '%' with an integer gives that element of the array. Negative integers count from the end of the array. %(X.TRUE-TEXT.FALSE-TEXT) Specifies a ternary expression. The character following the X is arbitrary; the same character is used to separate the text for the 'true' result from that for the 'false' result. This separator may not appear in the TRUE-TEXT, except as part of a %-escape sequence. A ')' may appear in the FALSE-TEXT as '%)'. TRUE-TEXT and FALSE-TEXT may both contain arbitrarily-nested escape sequences, including further ternary expressions. The left parenthesis may be preceded or followed by a positive integer N, which defaults to zero. A negative integer will be multiplied by -1, except as noted below for 'l'. The test character X may be any of the following: ! True if the shell is running with privileges. # True if the effective uid of the current process is N. ? True if the exit status of the last command was N. _ True if at least N shell constructs were started. C / True if the current absolute path has at least N elements relative to the root directory, hence / is counted as 0 elements. c . ~ True if the current path, with prefix replacement, has at least N elements relative to the root directory, hence / is counted as 0 elements. D True if the month is equal to N (January = 0). d True if the day of the month is equal to N. e True if the evaluation depth is at least N. g True if the effective gid of the current process is N. j True if the number of jobs is at least N. L True if the SHLVL parameter is at least N. l True if at least N characters have already been printed on the current line. When N is negative, true if at least abs(N) characters remain before the opposite margin (thus the left margin for RPROMPT). S True if the SECONDS parameter is at least N. T True if the time in hours is equal to N. t True if the time in minutes is equal to N. v True if the array psvar has at least N elements. V True if element N of the array psvar is set and non-empty. w True if the day of the week is equal to N (Sunday = 0). %STRING> %[XSTRING] Specifies truncation behaviour for the remainder of the prompt string. The third, deprecated, form is equivalent to '%XSTRINGX', i.e. X may be '<' or '>'. The STRING will be displayed in place of the truncated portion of any string; note this does not undergo prompt expansion. The numeric argument, which in the third form may appear immediately after the '[', specifies the maximum permitted length of the various strings that can be displayed in the prompt. In the first two forms, this numeric argument may be negative, in which case the truncation length is determined by subtracting the absolute value of the numeric argument from the number of character positions remaining on the current prompt line. If this results in a zero or negative length, a length of 1 is used. In other words, a negative argument arranges that after truncation at least N characters remain before the right margin (left margin for RPROMPT). The forms with '<' truncate at the left of the string, and the forms with '>' truncate at the right of the string. For example, if the current directory is '/home/pike', the prompt '%8<..<%/' will expand to '..e/pike'. In this string, the terminating character ('<', '>' or ']'), or in fact any character, may be quoted by a preceding '\'; note when using print -P, however, that this must be doubled as the string is also subject to standard print processing, in addition to any backslashes removed by a double quoted string: the worst case is therefore 'print -P "%<\\\\<<..."'. If the STRING is longer than the specified truncation length, it will appear in full, completely replacing the truncated string. The part of the prompt string to be truncated runs to the end of the string, or to the end of the next enclosing group of the '%(' construct, or to the next truncation encountered at the same grouping level (i.e. truncations inside a '%(' are separate), which ever comes first. In particular, a truncation with argument zero (e.g., '%<<') marks the end of the range of the string to be truncated while turning off truncation from there on. For example, the prompt '%10<...<%~%<<%# ' will print a truncated representation of the current directory, followed by a '%' or '#', followed by a space. Without the '%<<', those two characters would be included in the string to be truncated. Note that '%-0<<' is not equivalent to '%<<' but specifies that the prompt is truncated at the right margin. Truncation applies only within each individual line of the prompt, as delimited by embedded newlines (if any). If the total length of any line of the prompt after truncation is greater than the terminal width, or if the part to be truncated contains embedded newlines, truncation behavior is undefined and may change in a future version of the shell. Use '%-N(l.TRUE-TEXT.FALSE-TEXT)' to remove parts of the prompt when the available space is less than N.  File: zsh.info, Node: Expansion, Next: Parameters, Prev: Prompt Expansion, Up: Top 14 Expansion ************ The following types of expansions are performed in the indicated order in five steps: _History Expansion_ This is performed only in interactive shells. _Alias Expansion_ Aliases are expanded immediately before the command line is parsed as explained in *note Aliasing::. _Process Substitution_ _Parameter Expansion_ _Command Substitution_ _Arithmetic Expansion_ _Brace Expansion_ These five are performed in left-to-right fashion. On each argument, any of the five steps that are needed are performed one after the other. Hence, for example, all the parts of parameter expansion are completed before command substitution is started. After these expansions, all unquoted occurrences of the characters '\',''' and '"' are removed. _Filename Expansion_ If the SH_FILE_EXPANSION option is set, the order of expansion is modified for compatibility with ‘sh’ and ‘ksh’. In that case _filename expansion_ is performed immediately after _alias expansion_, preceding the set of five expansions mentioned above. _Filename Generation_ This expansion, commonly referred to as ‘globbing’, is always done last. The following sections explain the types of expansion in detail. * Menu: * History Expansion:: * Process Substitution:: * Parameter Expansion:: * Command Substitution:: * Arithmetic Expansion:: * Brace Expansion:: * Filename Expansion:: * Filename Generation::  File: zsh.info, Node: History Expansion, Next: Process Substitution, Up: Expansion 14.1 History Expansion ====================== History expansion allows you to use words from previous command lines in the command line you are typing. This simplifies spelling corrections and the repetition of complicated commands or arguments. Immediately before execution, each command is saved in the history list, the size of which is controlled by the HISTSIZE parameter. The one most recent command is always retained in any case. Each saved command in the history list is called a history _event_ and is assigned a number, beginning with 1 (one) when the shell starts up. The history number that you may see in your prompt (see *note Prompt Expansion::) is the number that is to be assigned to the _next_ command. * Menu: * Overview:: * Event Designators:: * Word Designators:: * Modifiers::  File: zsh.info, Node: Overview, Next: Event Designators, Up: History Expansion 14.1.1 Overview --------------- A history expansion begins with the first character of the histchars parameter, which is '!' by default, and may occur anywhere on the command line, including inside double quotes (but not inside single quotes '...' or C-style quotes $'...' nor when escaped with a backslash). The first character is followed by an optional event designator (*note Event Designators::) and then an optional word designator (*note Word Designators::); if neither of these designators is present, no history expansion occurs. Input lines containing history expansions are echoed after being expanded, but before any other expansions take place and before the command is executed. It is this expanded form that is recorded as the history event for later references. History expansions do not nest. By default, a history reference with no event designator refers to the same event as any preceding history reference on that command line; if it is the only history reference in a command, it refers to the previous command. However, if the option CSH_JUNKIE_HISTORY is set, then every history reference with no event specification _always_ refers to the previous command. For example, '!' is the event designator for the previous command, so '!!:1' always refers to the first word of the previous command, and '!!$' always refers to the last word of the previous command. With CSH_JUNKIE_HISTORY set, then '!:1' and '!$' function in the same manner as '!!:1' and '!!$', respectively. Conversely, if CSH_JUNKIE_HISTORY is unset, then '!:1' and '!$' refer to the first and last words, respectively, of the same event referenced by the nearest other history reference preceding them on the current command line, or to the previous command if there is no preceding reference. The character sequence '^FOO^BAR' (where '^' is actually the second character of the histchars parameter) repeats the last command, replacing the string FOO with BAR. More precisely, the sequence '^FOO^BAR^' is synonymous with '!!:s^FOO^BAR^', hence other modifiers (see *note Modifiers::) may follow the final '^'. In particular, '^FOO^BAR^:G' performs a global substitution. If the shell encounters the character sequence '!"' in the input, the history mechanism is temporarily disabled until the current list (see *note Shell Grammar::) is fully parsed. The '!"' is removed from the input, and any subsequent '!' characters have no special significance. A less convenient but more comprehensible form of command history support is provided by the fc builtin.  File: zsh.info, Node: Event Designators, Next: Word Designators, Prev: Overview, Up: History Expansion 14.1.2 Event Designators ------------------------ An event designator is a reference to a command-line entry in the history list. In the list below, remember that the initial `!' in each item may be changed to another character by setting the histchars parameter. ! Start a history expansion, except when followed by a blank, newline, '=' or '('. If followed immediately by a word designator (*note Word Designators::), this forms a history reference with no event designator (*note Overview::). !! Refer to the previous command. By itself, this expansion repeats the previous command. !N Refer to command-line N. !-N Refer to the current command-line minus N. !STR Refer to the most recent command starting with STR. !?STR[?] Refer to the most recent command containing STR. The trailing '?' is necessary if this reference is to be followed by a modifier or followed by any text that is not to be considered part of STR. !# Refer to the current command line typed in so far. The line is treated as if it were complete up to and including the word before the one with the '!#' reference. !{...} Insulate a history reference from adjacent characters (if necessary).  File: zsh.info, Node: Word Designators, Next: Modifiers, Prev: Event Designators, Up: History Expansion 14.1.3 Word Designators ----------------------- A word designator indicates which word or words of a given command line are to be included in a history reference. A ':' usually separates the event specification from the word designator. It may be omitted only if the word designator begins with a '^', '$', '*', '-' or '%'. Word designators include: 0 The first input word (command). N The Nth argument. ^ The first argument. That is, 1. $ The last argument. % The word matched by (the most recent) ?STR search. X-Y A range of words; X defaults to 0. * All the arguments, or a null value if there are none. X* Abbreviates 'X-$'. X- Like 'X*' but omitting word $. Note that a '%' word designator works only when used in one of '!%', '!:%' or '!?STR?:%', and only when used after a !? expansion (possibly in an earlier command). Anything else results in an error, although the error may not be the most obvious one.  File: zsh.info, Node: Modifiers, Prev: Word Designators, Up: History Expansion 14.1.4 Modifiers ---------------- After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a ':'. These modifiers also work on the result of _filename generation_ and _parameter expansion_, except where noted. a Turn a file name into an absolute path: prepends the current directory, if necessary; remove '.' path segments; and remove '..' path segments and the segments that immediately precede them. This transformation is agnostic about what is in the filesystem, i.e. is on the logical, not the physical directory. It takes place in the same manner as when changing directories when neither of the options CHASE_DOTS or CHASE_LINKS is set. For example, '/before/here/../after' is always transformed to '/before/after', regardless of whether '/before/here' exists or what kind of object (dir, file, symlink, etc.) it is. A Turn a file name into an absolute path as the 'a' modifier does, and _then_ pass the result through the realpath(3) library function to resolve symbolic links. Note: on systems that do not have a realpath(3) library function, symbolic links are not resolved, so on those systems 'a' and 'A' are equivalent. Note: foo:A and realpath(foo) are different on some inputs. For realpath(foo) semantics, see the 'P' modifier. c Resolve a command name into an absolute path by searching the command path given by the PATH variable. This does not work for commands containing directory parts. Note also that this does not usually work as a glob qualifier unless a file of the same name is found in the current directory. e Remove all but the part of the filename extension following the '.'; see the definition of the filename extension in the description of the r modifier below. Note that according to that definition the result will be empty if the string ends with a '.'. h [ DIGITS ] Remove a trailing pathname component, shortening the path by one directory level: this is the 'head' of the pathname. This works like 'dirname'. If the h is followed immediately (with no spaces or other separator) by any number of decimal digits, and the value of the resulting number is non-zero, that number of leading components is preserved instead of the final component being removed. In an absolute path the leading '/' is the first component, so, for example, if var=/my/path/to/something, then ${var:h3} substitutes /my/path. Consecutive '/'s are treated the same as a single '/'. In parameter substitution, digits may only be used if the expression is in braces, so for example the short form substitution $var:h2 is treated as ${var:h}2, not as ${var:h2}. No restriction applies to the use of digits in history substitution or globbing qualifiers. If more components are requested than are present, the entire path is substituted (so this does not trigger a 'failed modifier' error in history expansion). l Convert the words to all lowercase. p Print the new command but do not execute it. Only works with history expansion. P Turn a file name into an absolute path, like realpath(3). The resulting path will be absolute, will refer to the same directory entry as the input filename, and none of its components will be symbolic links or equal to '.' or '..'. Unlike realpath(3), non-existent trailing components are permitted and preserved. q Quote the substituted words, escaping further substitutions. Works with history expansion and parameter expansion, though for parameters it is only useful if the resulting text is to be re-evaluated such as by eval. Q Remove one level of quotes from the substituted words. r Remove a filename extension leaving the root name. Strings with no filename extension are not altered. A filename extension is a '.' followed by any number of characters (including zero) that are neither '.' nor '/' and that continue to the end of the string. For example, the extension of 'foo.orig.c' is '.c', and 'dir.c/foo' has no extension. s/L/R[/] Substitute R for L as described below. The substitution is done only for the first string that matches L. For arrays and for filename generation, this applies to each word of the expanded text. See below for further notes on substitutions. The forms 'gs/L/R' and 's/L/R/:G' perform global substitution, i.e. substitute every occurrence of R for L. Note that the g or :G must appear in exactly the position shown. See further notes on this form of substitution below. & Repeat the previous s substitution. Like s, may be preceded immediately by a g. In parameter expansion the & must appear inside braces, and in filename generation it must be quoted with a backslash. t [ DIGITS ] Remove all leading pathname components, leaving the final component (tail). This works like 'basename'. Any trailing slashes are first removed. Decimal digits are handled as described above for (h), but in this case that number of trailing components is preserved instead of the default 1; 0 is treated the same as 1. u Convert the words to all uppercase. x Like q, but break into words at whitespace. Does not work with parameter expansion. The s/L/R/ substitution works as follows. By default the left-hand side of substitutions are not patterns, but character strings. Any character can be used as the delimiter in place of '/'. A backslash quotes the delimiter character. The character '&', in the right-hand-side R, is replaced by the text from the left-hand-side L. The '&' can be quoted with a backslash. A null L uses the previous string either from the previous L or from the contextual scan string S from '!?S'. You can omit the rightmost delimiter if a newline immediately follows R; the rightmost '?' in a context scan can similarly be omitted. Note the same record of the last L and R is maintained across all forms of expansion. Note that if a '&' is used within glob qualifiers an extra backslash is needed as a & is a special character in this case. Also note that the order of expansions affects the interpretation of L and R. When used in a history expansion, which occurs before any other expansions, L and R are treated as literal strings (except as explained for HIST_SUBST_PATTERN below). When used in parameter expansion, the replacement of R into the parameter's value is done first, and then any additional process, parameter, command, arithmetic, or brace references are applied, which may evaluate those substitutions and expansions more than once if L appears more than once in the starting value. When used in a glob qualifier, any substitutions or expansions are performed once at the time the qualifier is parsed, even before the ':s' expression itself is divided into L and R sides. If the option HIST_SUBST_PATTERN is set, L is treated as a pattern of the usual form described in *note Filename Generation::. This can be used in all the places where modifiers are available; note, however, that in globbing qualifiers parameter substitution has already taken place, so parameters in the replacement string should be quoted to ensure they are replaced at the correct time. Note also that complicated patterns used in globbing qualifiers may need the extended glob qualifier notation (#q:s/.../.../) in order for the shell to recognize the expression as a glob qualifier. Further, note that bad patterns in the substitution are not subject to the NO_BAD_PATTERN option so will cause an error. When HIST_SUBST_PATTERN is set, L may start with a # to indicate that the pattern must match at the start of the string to be substituted, and a % may appear at the start or after an # to indicate that the pattern must match at the end of the string to be substituted. The % or # may be quoted with two backslashes. For example, the following piece of filename generation code with the EXTENDED_GLOB option: print -r -- *.c(#q:s/#%(#b)s(*).c/'S${match[1]}.C'/) takes the expansion of *.c and applies the glob qualifiers in the (#q...) expression, which consists of a substitution modifier anchored to the start and end of each word (#%). This turns on backreferences ((#b)), so that the parenthesised subexpression is available in the replacement string as ${match[1]}. The replacement string is quoted so that the parameter is not substituted before the start of filename generation. The following f, F, w and W modifiers work only with parameter expansion and filename generation. They are listed here to provide a single point of reference for all modifiers. f Repeats the immediately (without a colon) following modifier until the resulting word doesn't change any more. F:EXPR: Like f, but repeats only N times if the expression EXPR evaluates to N. Any character can be used instead of the ':'; if '(', '[', or '{' is used as the opening delimiter, the closing delimiter should be ')', ']', or '}', respectively. w Makes the immediately following modifier work on each word in the string. W:SEP: Like w but words are considered to be the parts of the string that are separated by SEP. Any character can be used instead of the ':'; opening parentheses are handled specially, see above.  File: zsh.info, Node: Process Substitution, Next: Parameter Expansion, Prev: History Expansion, Up: Expansion 14.2 Process Substitution ========================= Each part of a command argument that takes the form '<(LIST)', '>(LIST)' or '=(LIST)' is subject to process substitution. The expression may be preceded or followed by other strings except that, to prevent clashes with commonly occurring strings and patterns, the last form must occur at the start of a command argument, and the forms are only expanded when first parsing command or assignment arguments. Process substitutions may be used following redirection operators; in this case, the substitution must appear with no trailing string. Note that '<<(LIST)' is not a special syntax; it is equivalent to '< <(LIST)', redirecting standard input from the result of process substitution. Hence all the following documentation applies. The second form (with the space) is recommended for clarity. In the case of the < or > forms, the shell runs the commands in LIST as a subprocess of the job executing the shell command line. If the system supports the /dev/fd mechanism, the command argument is the name of the device file corresponding to a file descriptor; otherwise, if the system supports named pipes (FIFOs), the command argument will be a named pipe. If the form with > is selected then writing on this special file will provide input for LIST. If < is used, then the file passed as an argument will be connected to the output of the LIST process. For example, paste <(cut -f1 FILE1) <(cut -f3 FILE2) | tee >(PROCESS1) >(PROCESS2) >/dev/null cuts fields 1 and 3 from the files FILE1 and FILE2 respectively, pastes the results together, and sends it to the processes PROCESS1 and PROCESS2. If =(...) is used instead of <(...), then the file passed as an argument will be the name of a temporary file containing the output of the LIST process. This may be used instead of the < form for a program that expects to lseek (see lseek(2)) on the input file. There is an optimisation for substitutions of the form =(<< >(PROCESS1) > >(PROCESS2) The shell uses pipes instead of FIFOs to implement the latter two process substitutions in the above example. There is an additional problem with >(PROCESS); when this is attached to an external command, the parent shell does not wait for PROCESS to finish and hence an immediately following command cannot rely on the results being complete. The problem and solution are the same as described in the section _MULTIOS_ in *note Redirection::. Hence in a simplified version of the example above: paste <(cut -f1 FILE1) <(cut -f3 FILE2) > >(PROCESS) (note that no MULTIOS are involved), PROCESS will be run asynchronously as far as the parent shell is concerned. The workaround is: { paste <(cut -f1 FILE1) <(cut -f3 FILE2) } > >(PROCESS) The extra processes here are spawned from the parent shell which will wait for their completion. Another problem arises any time a job with a substitution that requires a temporary file is disowned by the shell, including the case where '&!' or '&|' appears at the end of a command containing a substitution. In that case the temporary file will not be cleaned up as the shell no longer has any memory of the job. A workaround is to use a subshell, for example, (mycmd =(myoutput)) &! as the forked subshell will wait for the command to finish then remove the temporary file. A general workaround to ensure a process substitution endures for an appropriate length of time is to pass it as a parameter to an anonymous shell function (a piece of shell code that is run immediately with function scope). For example, this code: () { print File $1: cat $1 } =(print This be the verse) outputs something resembling the following File /tmp/zsh6nU0kS: This be the verse The temporary file created by the process substitution will be deleted when the function exits.  File: zsh.info, Node: Parameter Expansion, Next: Command Substitution, Prev: Process Substitution, Up: Expansion 14.3 Parameter Expansion ======================== The character '$' is used to introduce parameter expansions. See *note Parameters:: for a description of parameters, including arrays, associative arrays, and subscript notation to access individual array elements. Note in particular the fact that words of unquoted parameters are not automatically split on whitespace unless the option SH_WORD_SPLIT is set; see references to this option below for more details. This is an important difference from other shells. However, as in other shells, null words are elided from unquoted parameters' expansions. With default options, after the assignments: array=("first word" "" "third word") scalar="only word" then $array substitutes two words, 'first word' and 'third word', and $scalar substitutes a single word 'only word'. Note that second element of array was elided. Scalar parameters can be elided too if their value is null (empty). To avoid elision, use quoting as follows: "$scalar" for scalars and "${array[@]}" or "${(@)array}" for arrays. (The last two forms are equivalent.) Parameter expansions can involve _flags_, as in '${(@kv)aliases}', and other operators, such as '${PREFIX:-"/usr/local"}'. Parameter expansions can also be nested. These topics will be introduced below. The full rules are complicated and are noted at the end. In the expansions discussed below that require a pattern, the form of the pattern is the same as that used for filename generation; see *note Filename Generation::. Note that these patterns, along with the replacement text of any substitutions, are themselves subject to parameter expansion, command substitution, and arithmetic expansion. In addition to the following operations, the colon modifiers described in *note Modifiers:: in *note History Expansion:: can be applied: for example, ${i:s/foo/bar/} performs string substitution on the expansion of parameter $i. In the following descriptions, 'WORD' refers to a single word substituted on the command line, not necessarily a space delimited word. ${NAME} The value, if any, of the parameter NAME is substituted. The braces are required if the expansion is to be followed by a letter, digit, or underscore that is not to be interpreted as part of NAME. In addition, more complicated forms of substitution usually require the braces to be present; exceptions, which only apply if the option KSH_ARRAYS is not set, are a single subscript or any colon modifiers appearing after the name, or any of the characters '^', '=', '~', '#' or '+' appearing before the name, all of which work with or without braces. If NAME is an array parameter, and the KSH_ARRAYS option is not set, then the value of each element of NAME is substituted, one element per word. Otherwise, the expansion results in one word only; with KSH_ARRAYS, this is the first element of an array. No field splitting is done on the result unless the SH_WORD_SPLIT option is set. See also the flags = and s:STRING:. ${+NAME} If NAME is the name of a set parameter '1' is substituted, otherwise '0' is substituted. ${NAME-WORD} ${NAME:-WORD} If NAME is set, or in the second form is non-null, then substitute its value; otherwise substitute WORD. In the second form NAME may be omitted, in which case WORD is always substituted. ${NAME+WORD} ${NAME:+WORD} If NAME is set, or in the second form is non-null, then substitute WORD; otherwise substitute nothing. ${NAME=WORD} ${NAME:=WORD} ${NAME::=WORD} In the first form, if NAME is unset then set it to WORD; in the second form, if NAME is unset or null then set it to WORD; and in the third form, unconditionally set NAME to WORD. In all forms, the value of the parameter is then substituted. ${NAME?WORD} ${NAME:?WORD} In the first form, if NAME is set, or in the second form if NAME is both set and non-null, then substitute its value; otherwise, print WORD and exit from the shell. Interactive shells instead return to the prompt. If WORD is omitted, then a standard message is printed. In any of the above expressions that test a variable and substitute an alternate WORD, note that you can use standard shell quoting in the WORD value to selectively override the splitting done by the SH_WORD_SPLIT option and the = flag, but not splitting by the s:STRING: flag. In the following expressions, when NAME is an array and the substitution is not quoted, or if the '(@)' flag or the NAME[@] syntax is used, matching and replacement is performed on each array element separately. ${NAME#PATTERN} ${NAME##PATTERN} If the PATTERN matches the beginning of the value of NAME, then substitute the value of NAME with the matched portion deleted; otherwise, just substitute the value of NAME. In the first form, the smallest matching pattern is preferred; in the second form, the largest matching pattern is preferred. ${NAME%PATTERN} ${NAME%%PATTERN} If the PATTERN matches the end of the value of NAME, then substitute the value of NAME with the matched portion deleted; otherwise, just substitute the value of NAME. In the first form, the smallest matching pattern is preferred; in the second form, the largest matching pattern is preferred. ${NAME:#PATTERN} If the PATTERN matches the value of NAME, then substitute the empty string; otherwise, just substitute the value of NAME. If NAME is an array the matching array elements are removed (use the '(M)' flag to remove the non-matched elements). ${NAME:|ARRAYNAME} If ARRAYNAME is the name (N.B., not contents) of an array variable, then any elements contained in ARRAYNAME are removed from the substitution of NAME. If the substitution is scalar, either because NAME is a scalar variable or the expression is quoted, the elements of ARRAYNAME are instead tested against the entire expression. ${NAME:*ARRAYNAME} Similar to the preceding substitution, but in the opposite sense, so that entries present in both the original substitution and as elements of ARRAYNAME are retained and others removed. ${NAME:^ARRAYNAME} ${NAME:^^ARRAYNAME} Zips two arrays, such that the output array is twice as long as the shortest (longest for ':^^') of name and arrayname, with the elements alternatingly being picked from them. For ':^', if one of the input arrays is longer, the output will stop when the end of the shorter array is reached. Thus, a=(1 2 3 4); b=(a b); print ${a:^b} will output '1 a 2 b'. For ':^^', then the input is repeated until all of the longer array has been used up and the above will output '1 a 2 b 3 a 4 b'. Either or both inputs may be a scalar, they will be treated as an array of length 1 with the scalar as the only element. If either array is empty, the other array is output with no extra elements inserted. Currently the following code will output 'a b' and '1' as two separate elements, which can be unexpected. The second print provides a workaround which should continue to work if this is changed. a=(a b); b=(1 2); print -l "${a:^b}"; print -l "${${a:^b}}" ${NAME:OFFSET} ${NAME:OFFSET:LENGTH} This syntax gives effects similar to parameter subscripting in the form $NAME[START,END], but is compatible with other shells; note that both OFFSET and LENGTH are interpreted differently from the components of a subscript. If OFFSET is non-negative, then if the variable NAME is a scalar substitute the contents starting OFFSET characters from the first character of the string, and if NAME is an array substitute elements starting OFFSET elements from the first element. If LENGTH is given, substitute that many characters or elements, otherwise the entire rest of the scalar or array. A positive OFFSET is always treated as the offset of a character or element in NAME from the first character or element of the array (this is different from native zsh subscript notation). Hence 0 refers to the first character or element regardless of the setting of the option KSH_ARRAYS. A negative offset counts backwards from the end of the scalar or array, so that -1 corresponds to the last character or element, and so on. When positive, LENGTH counts from the OFFSET position toward the end of the scalar or array. When negative, LENGTH counts back from the end. If this results in a position smaller than OFFSET, a diagnostic is printed and nothing is substituted. The option MULTIBYTE is obeyed, i.e. the offset and length count multibyte characters where appropriate. OFFSET and LENGTH undergo the same set of shell substitutions as for scalar assignment; in addition, they are then subject to arithmetic evaluation. Hence, for example print ${foo:3} print ${foo: 1 + 2} print ${foo:$(( 1 + 2))} print ${foo:$(echo 1 + 2)} all have the same effect, extracting the string starting at the fourth character of $foo if the substitution would otherwise return a scalar, or the array starting at the fourth element if $foo would return an array. Note that with the option KSH_ARRAYS $foo always returns a scalar (regardless of the use of the offset syntax) and a form such as ${foo[*]:3} is required to extract elements of an array named foo. If OFFSET is negative, the - may not appear immediately after the : as this indicates the ${NAME:-WORD} form of substitution. Instead, a space may be inserted before the -. Furthermore, neither OFFSET nor LENGTH may begin with an alphabetic character or & as these are used to indicate history-style modifiers. To substitute a value from a variable, the recommended approach is to precede it with a $ as this signifies the intention (parameter substitution can easily be rendered unreadable); however, as arithmetic substitution is performed, the expression ${var: offs} does work, retrieving the offset from $offs. For further compatibility with other shells there is a special case for array offset 0. This usually accesses the first element of the array. However, if the substitution refers to the positional parameter array, e.g. $@ or $*, then offset 0 instead refers to $0, offset 1 refers to $1, and so on. In other words, the positional parameter array is effectively extended by prepending $0. Hence ${*:0:1} substitutes $0 and ${*:1:1} substitutes $1. ${NAME/PATTERN/REPL} ${NAME//PATTERN/REPL} ${NAME:/PATTERN/REPL} Replace the longest possible match of PATTERN in the expansion of parameter NAME by string REPL. The first form replaces just the first occurrence, the second form all occurrences, and the third form replaces only if PATTERN matches the entire string. Both PATTERN and REPL are subject to double-quoted substitution, so that expressions like ${name/$opat/$npat} will work, but obey the usual rule that pattern characters in $opat are not treated specially unless either the option GLOB_SUBST is set, or $opat is instead substituted as ${~opat}. The PATTERN may begin with a '#', in which case the PATTERN must match at the start of the string, or '%', in which case it must match at the end of the string, or '#%' in which case the PATTERN must match the entire string. The REPL may be an empty string, in which case the final '/' may also be omitted. To quote the final '/' in other cases it should be preceded by a single backslash; this is not necessary if the '/' occurs inside a substituted parameter. Note also that the '#', '%' and '#% are not active if they occur inside a substituted parameter, even at the start. If, after quoting rules apply, ${NAME} expands to an array, the replacements act on each element individually. Note also the effect of the I and S parameter expansion flags below; however, the flags M, R, B, E and N are not useful. For example, foo="twinkle twinkle little star" sub="t*e" rep="spy" print ${foo//${~sub}/$rep} print ${(S)foo//${~sub}/$rep} Here, the '~' ensures that the text of $sub is treated as a pattern rather than a plain string. In the first case, the longest match for t*e is substituted and the result is 'spy star', while in the second case, the shortest matches are taken and the result is 'spy spy lispy star'. ${#SPEC} If SPEC is one of the above substitutions, substitute the length in characters of the result instead of the result itself. If SPEC is an array expression, substitute the number of elements of the result. This has the side-effect that joining is skipped even in quoted forms, which may affect other sub-expressions in SPEC. Note that '^', '=', and '~', below, must appear to the left of '#' when these forms are combined. If the option POSIX_IDENTIFIERS is not set, and SPEC is a simple name, then the braces are optional; this is true even for special parameters so e.g. $#- and $#* take the length of the string $- and the array $* respectively. If POSIX_IDENTIFIERS is set, then braces are required for the # to be treated in this fashion. ${^SPEC} ${^^SPEC} Turn on the RC_EXPAND_PARAM option for the evaluation of SPEC; if the '^' is doubled, turn it off. When this option is set, array expansions of the form FOO${XX}BAR, where the parameter XX is set to (A B C), are substituted with 'FOOABAR FOOBBAR FOOCBAR' instead of the default 'FOOA B CBAR'. Note that an empty array will therefore cause all arguments to be removed. Internally, each such expansion is converted into the equivalent list for brace expansion. E.g., ${^var} becomes {$var[1],$var[2],...}, and is processed as described in *note Brace Expansion:: below: note, however, the expansion happens immediately, with any explicit brace expansion happening later. If word splitting is also in effect the $var[N] may themselves be split into different list elements. ${=SPEC} ${==SPEC} Perform word splitting using the rules for SH_WORD_SPLIT during the evaluation of SPEC, but regardless of whether the parameter appears in double quotes; if the '=' is doubled, turn it off. This forces parameter expansions to be split into separate words before substitution, using IFS as a delimiter. This is done by default in most other shells. Note that splitting is applied to WORD in the assignment forms of SPEC _before_ the assignment to NAME is performed. This affects the result of array assignments with the A flag. ${~SPEC} ${~~SPEC} Turn on the GLOB_SUBST option for the evaluation of SPEC; if the '~' is doubled, turn it off. When this option is set, the string resulting from the expansion will be interpreted as a pattern anywhere that is possible, such as in filename expansion and filename generation and pattern-matching contexts like the right hand side of the '=' and '!=' operators in conditions. In nested substitutions, note that the effect of the ~ applies to the result of the current level of substitution. A surrounding pattern operation on the result may cancel it. Hence, for example, if the parameter foo is set to *, ${~foo//\*/*.c} is substituted by the pattern *.c, which may be expanded by filename generation, but ${${~foo}//\*/*.c} substitutes to the string *.c, which will not be further expanded. If a ${...} type parameter expression or a $(...) type command substitution is used in place of NAME above, it is expanded first and the result is used as if it were the value of NAME. Thus it is possible to perform nested operations: ${${foo#head}%tail} substitutes the value of $foo with both 'head' and 'tail' deleted. The form with $(...) is often useful in combination with the flags described next; see the examples below. Each NAME or nested ${...} in a parameter expansion may also be followed by a subscript expression as described in *note Array Parameters::. Note that double quotes may appear around nested expressions, in which case only the part inside is treated as quoted; for example, ${(f)"$(foo)"} quotes the result of $(foo), but the flag '(f)' (see below) is applied using the rules for unquoted expansions. Note further that quotes are themselves nested in this context; for example, in "${(@f)"$(foo)"}", there are two sets of quotes, one surrounding the whole expression, the other (redundant) surrounding the $(foo) as before. 14.3.1 Parameter Expansion Flags -------------------------------- If the opening brace is directly followed by an opening parenthesis, the string up to the matching closing parenthesis will be taken as a list of flags. In cases where repeating a flag is meaningful, the repetitions need not be consecutive; for example, '(q%q%q)' means the same thing as the more readable '(%%qqq)'. The following flags are supported: # Evaluate the resulting words as numeric expressions and interpret these as character codes. Output the corresponding characters. Note that this form is entirely distinct from use of the # without parentheses. If the MULTIBYTE option is set and the number is greater than 127 (i.e. not an ASCII character) it is treated as a Unicode character. % Expand all % escapes in the resulting words in the same way as in prompts (see *note Prompt Expansion::). If this flag is given twice, full prompt expansion is done on the resulting words, depending on the setting of the PROMPT_PERCENT, PROMPT_SUBST and PROMPT_BANG options. @ In double quotes, array elements are put into separate words. E.g., '"${(@)foo}"' is equivalent to '"${foo[@]}"' and '"${(@)foo[1,2]}"' is the same as '"$foo[1]" "$foo[2]"'. This is distinct from _field splitting_ by the f, s or z flags, which still applies within each array element. A Convert the substitution into an array expression, even if it otherwise would be scalar. This has lower precedence than subscripting, so one level of nested expansion is required in order that subscripts apply to array elements. Thus ${${(A)NAME}[1]} yields the full value of NAME when NAME is scalar. This assigns an array parameter with '${...=...}', '${...:=...}' or '${...::=...}'. If this flag is repeated (as in 'AA'), assigns an associative array parameter. Assignment is made before sorting or padding; if field splitting is active, the WORD part is split before assignment. The NAME part may be a subscripted range for ordinary arrays; when assigning an associative array, the WORD part _must_ be converted to an array, for example by using '${(AA)=NAME=...}' to activate field splitting. Surrounding context such as additional nesting or use of the value in a scalar assignment may cause the array to be joined back into a single string again. a Sort in array index order; when combined with 'O' sort in reverse array index order. Note that 'a' is therefore equivalent to the default but 'Oa' is useful for obtaining an array's elements in reverse order. b Quote with backslashes only characters that are special to pattern matching. This is useful when the contents of the variable are to be tested using GLOB_SUBST, including the ${~...} switch. Quoting using one of the q family of flags does not work for this purpose since quotes are not stripped from non-pattern characters by GLOB_SUBST. In other words, pattern=${(q)str} [[ $str = ${~pattern} ]] works if $str is 'a*b' but not if it is 'a b', whereas pattern=${(b)str} [[ $str = ${~pattern} ]] is always true for any possible value of $str. c With ${#NAME}, count the total number of characters in an array, as if the elements were concatenated with spaces between them. This is not a true join of the array, so other expressions used with this flag may have an effect on the elements of the array before it is counted. C Capitalize the resulting words. 'Words' in this case refers to sequences of alphanumeric characters separated by non-alphanumerics, _not_ to words that result from field splitting. D Assume the string or array elements contain directories and attempt to substitute the leading part of these by names. The remainder of the path (the whole of it if the leading part was not substituted) is then quoted so that the whole string can be used as a shell argument. This is the reverse of '~' substitution: see *note Filename Expansion::. e Perform single word shell expansions, namely _parameter expansion_, _command substitution_ and _arithmetic expansion_, on the result. Such expansions can be nested but too deep recursion may have unpredictable effects. f Split the result of the expansion at newlines. This is a shorthand for 'ps:\n:'. F Join the words of arrays together using newline as a separator. This is a shorthand for 'pj:\n:'. g:OPTS: Process escape sequences like the echo builtin when no options are given (g::). With the o option, octal escapes don't take a leading zero. With the c option, sequences like '^X' are also processed. With the e option, processes '\M-t' and similar sequences like the print builtin. With both of the o and e options, behaves like the print builtin except that in none of these modes is '\c' interpreted. i Sort case-insensitively. May be combined with 'n' or 'O'. k If NAME refers to an associative array, substitute the _keys_ (element names) rather than the values of the elements. Used with subscripts (including ordinary arrays), force indices or keys to be substituted even if the subscript form refers to values. However, this flag may not be combined with subscript ranges. With the KSH_ARRAYS option a subscript '[*]' or '[@]' is needed to operate on the whole array, as usual. L Convert all letters in the result to lower case. n Sort decimal integers numerically; if the first differing characters of two test strings are not digits, sorting is lexical. '+' and '-' are not treated specially; they are treated as any other non-digit. Integers with more initial zeroes are sorted before those with fewer or none. Hence the array 'foo+24 foo1 foo02 foo2 foo3 foo20 foo23' is sorted into the order shown. May be combined with 'i' or 'O'. - As n, but a leading minus sign indicates a negative decimal integer. A leading minus sign not followed by an integer does not trigger numeric sorting. Note that '+' signs are not handled specially (this may change in the future). o Sort the resulting words in ascending order; if this appears on its own the sorting is lexical and case-sensitive (unless the locale renders it case-insensitive). Sorting in ascending order is the default for other forms of sorting, so this is ignored if combined with 'a', 'i', 'n' or '-'. O Sort the resulting words in descending order; 'O' without 'a', 'i', 'n' or '-' sorts in reverse lexical order. May be combined with 'a', 'i', 'n' or '-' to reverse the order of sorting. P This forces the value of the parameter NAME to be interpreted as a further parameter name, whose value will be used where appropriate. Note that flags set with one of the typeset family of commands (in particular case transformations) are not applied to the value of NAME used in this fashion. If used with a nested parameter or command substitution, the result of that will be taken as a parameter name in the same way. For example, if you have 'foo=bar' and 'bar=baz', the strings ${(P)foo}, ${(P)${foo}}, and ${(P)$(echo bar)} will be expanded to 'baz'. Likewise, if the reference is itself nested, the expression with the flag is treated as if it were directly replaced by the parameter name. It is an error if this nested substitution produces an array with more than one word. For example, if 'name=assoc' where the parameter assoc is an associative array, then '${${(P)name}[elt]}' refers to the element of the associative subscripted 'elt'. q Quote characters that are special to the shell in the resulting words with backslashes; unprintable or invalid characters are quoted using the $'\NNN' form, with separate quotes for each octet. If this flag is given twice, the resulting words are quoted in single quotes and if it is given three times, the words are quoted in double quotes; in these forms no special handling of unprintable or invalid characters is attempted. If the flag is given four times, the words are quoted in single quotes preceded by a $. Note that in all three of these forms quoting is done unconditionally, even if this does not change the way the resulting string would be interpreted by the shell. If a q- is given (only a single q may appear), a minimal form of single quoting is used that only quotes the string if needed to protect special characters. Typically this form gives the most readable output. If a q+ is given, an extended form of minimal quoting is used that causes unprintable characters to be rendered using $'...'. This quoting is similar to that used by the output of values by the typeset family of commands. Q Remove one level of quotes from the resulting words. t Use a string describing the type of the parameter where the value of the parameter would usually appear. This string consists of keywords separated by hyphens ('-'). The first keyword in the string describes the main type, it can be one of 'scalar', 'array', 'integer', 'float' or 'association'. The other keywords describe the type in more detail: local for local parameters left for left justified parameters right_blanks for right justified parameters with leading blanks right_zeros for right justified parameters with leading zeros lower for parameters whose value is converted to all lower case when it is expanded upper for parameters whose value is converted to all upper case when it is expanded readonly for readonly parameters tag for tagged parameters tied for parameters tied to another parameter in the manner of PATH (colon-separated list) and path (array), whether these are special parameters or user-defined with 'typeset -T' export for exported parameters unique for arrays which keep only the first occurrence of duplicated values hide for parameters with the 'hide' flag hideval for parameters with the 'hideval' flag special for special parameters defined by the shell u Expand only the first occurrence of each unique word. U Convert all letters in the result to upper case. v Used with k, substitute (as two consecutive words) both the key and the value of each associative array element. Used with subscripts, force values to be substituted even if the subscript form refers to indices or keys. V Make any special characters in the resulting words visible. w With ${#NAME}, count words in arrays or strings; the s flag may be used to set a word delimiter. W Similar to w with the difference that empty words between repeated delimiters are also counted. X With this flag, parsing errors occurring with the Q, e and # flags or the pattern matching forms such as '${NAME#PATTERN}' are reported. Without the flag, errors are silently ignored. z Split the result of the expansion into words using shell parsing to find the words, i.e. taking into account any quoting in the value. Comments are not treated specially but as ordinary strings, similar to interactive shells with the INTERACTIVE_COMMENTS option unset (however, see the Z flag below for related options) Note that this is done very late, even later than the '(s)' flag. So to access single words in the result use nested expansions as in '${${(z)foo}[2]}'. Likewise, to remove the quotes in the resulting words use '${(Q)${(z)foo}}'. 0 Split the result of the expansion on null bytes. This is a shorthand for 'ps:\0:'. The following flags (except p) are followed by one or more arguments as shown. Any character, or the matching pairs '(...)', '{...}', '[...]', or '<...>', may be used in place of a colon as delimiters, but note that when a flag takes more than one argument, a matched pair of delimiters must surround each argument. p Recognize the same escape sequences as the print builtin in string arguments to any of the flags described below that follow this argument. Alternatively, with this option string arguments may be in the form $VAR in which case the value of the variable is substituted. Note this form is strict; the string argument does not undergo general parameter expansion. For example, sep=: val=a:b:c print ${(ps.$sep.)val} splits the variable on a :. ~ Strings inserted into the expansion by any of the flags below are to be treated as patterns. This applies to the string arguments of flags that follow ~ within the same set of parentheses. Compare with ~ outside parentheses, which forces the entire substituted string to be treated as a pattern. Hence, for example, [[ "?" = ${(~j.|.)array} ]] treats '|' as a pattern and succeeds if and only if $array contains the string '?' as an element. The ~ may be repeated to toggle the behaviour; its effect only lasts to the end of the parenthesised group. j:STRING: Join the words of arrays together using STRING as a separator. Note that this occurs before field splitting by the s:STRING: flag or the SH_WORD_SPLIT option. l:EXPR::STRING1::STRING2: Pad the resulting words on the left. Each word will be truncated if required and placed in a field EXPR characters wide. The arguments :STRING1: and :STRING2: are optional; neither, the first, or both may be given. Note that the same pairs of delimiters must be used for each of the three arguments. The space to the left will be filled with STRING1 (concatenated as often as needed) or spaces if STRING1 is not given. If both STRING1 and STRING2 are given, STRING2 is inserted once directly to the left of each word, truncated if necessary, before STRING1 is used to produce any remaining padding. If either of STRING1 or STRING2 is present but empty, i.e. there are two delimiters together at that point, the first character of $IFS is used instead. If the MULTIBYTE option is in effect, the flag m may also be given, in which case widths will be used for the calculation of padding; otherwise individual multibyte characters are treated as occupying one unit of width. If the MULTIBYTE option is not in effect, each byte in the string is treated as occupying one unit of width. Control characters are always assumed to be one unit wide; this allows the mechanism to be used for generating repetitions of control characters. m Only useful together with one of the flags l or r or with the # length operator when the MULTIBYTE option is in effect. Use the character width reported by the system in calculating how much of the string it occupies or the overall length of the string. Most printable characters have a width of one unit, however certain Asian character sets and certain special effects use wider characters; combining characters have zero width. Non-printable characters are arbitrarily counted as zero width; how they would actually be displayed will vary. If the m is repeated, the character either counts zero (if it has zero width), else one. For printable character strings this has the effect of counting the number of glyphs (visibly separate characters), except for the case where combining characters themselves have non-zero width (true in certain alphabets). r:EXPR::STRING1::STRING2: As l, but pad the words on the right and insert STRING2 immediately to the right of the string to be padded. Left and right padding may be used together. In this case the strategy is to apply left padding to the first half width of each of the resulting words, and right padding to the second half. If the string to be padded has odd width the extra padding is applied on the left. s:STRING: Force field splitting at the separator STRING. Note that a STRING of two or more characters means that all of them must match in sequence; this differs from the treatment of two or more characters in the IFS parameter. See also the = flag and the SH_WORD_SPLIT option. An empty string may also be given in which case every character will be a separate element. For historical reasons, the usual behaviour that empty array elements are retained inside double quotes is disabled for arrays generated by splitting; hence the following: line="one::three" print -l "${(s.:.)line}" produces two lines of output for one and three and elides the empty field. To override this behaviour, supply the '(@)' flag as well, i.e. "${(@s.:.)line}". Z:OPTS: As z but takes a combination of option letters between a following pair of delimiter characters. With no options the effect is identical to z. The following options are available: (Z+c+) causes comments to be parsed as a string and retained; any field in the resulting array beginning with an unquoted comment character is a comment. (Z+C+) causes comments to be parsed and removed. The rule for comments is standard: anything between a word starting with the third character of $HISTCHARS, default #, up to the next newline is a comment. (Z+n+) causes unquoted newlines to be treated as ordinary whitespace, else they are treated as if they are shell code delimiters and converted to semicolons. Options are combined within the same set of delimiters, e.g. (Z+Cn+). _:FLAGS: The underscore (_) flag is reserved for future use. As of this revision of zsh, there are no valid FLAGS; anything following an underscore, other than an empty pair of delimiters, is treated as an error, and the flag itself has no effect. The following flags are meaningful with the ${...#...} or ${...%...} forms. The S, I, and * flags may also be used with the ${.../...} forms. S With # or ##, search for the match that starts closest to the start of the string (a 'substring match'). Of all matches at a particular position, # selects the shortest and ## the longest: % str="aXbXc" % echo ${(S)str#X*} abXc % echo ${(S)str##X*} a % With % or %%, search for the match that starts closest to the end of the string: % str="aXbXc" % echo ${(S)str%X*} aXbc % echo ${(S)str%%X*} aXb % (Note that % and %% don't search for the match that ends closest to the end of the string, as one might expect.) With substitution via ${.../...} or ${...//...}, specifies non-greedy matching, i.e. that the shortest instead of the longest match should be replaced: % str="abab" % echo ${str/*b/_} _ % echo ${(S)str/*b/_} _ab % I:EXPR: Search the EXPRth match (where EXPR evaluates to a number). This only applies when searching for substrings, either with the S flag, or with ${.../...} (only the EXPRth match is substituted) or ${...//...} (all matches from the EXPRth on are substituted). The default is to take the first match. The EXPRth match is counted such that there is either one or zero matches from each starting position in the string, although for global substitution matches overlapping previous replacements are ignored. With the ${...%...} and ${...%%...} forms, the starting position for the match moves backwards from the end as the index increases, while with the other forms it moves forward from the start. Hence with the string which switch is the right switch for Ipswich? substitutions of the form ${(SI:N:)string#w*ch} as N increases from 1 will match and remove 'which', 'witch', 'witch' and 'wich'; the form using '##' will match and remove 'which switch is the right switch for Ipswich', 'witch is the right switch for Ipswich', 'witch for Ipswich' and 'wich'. The form using '%' will remove the same matches as for '#', but in reverse order, and the form using '%%' will remove the same matches as for '##' in reverse order. * Enable EXTENDED_GLOB for substitution via ${.../...} or ${...//...}. Note that '**' does not disable extendedglob. B Include the index of the beginning of the match in the result. E Include the index one character past the end of the match in the result (note this is inconsistent with other uses of parameter index). M Include the matched portion in the result. N Include the length of the match in the result. R Include the unmatched portion in the result (the _R_est). 14.3.2 Rules ------------ Here is a summary of the rules for substitution; this assumes that braces are present around the substitution, i.e. ${...}. Some particular examples are given below. Note that the Zsh Development Group accepts _no responsibility_ for any brain damage which may occur during the reading of the following rules. 1. _Nested substitution_ If multiple nested ${...} forms are present, substitution is performed from the inside outwards. At each level, the substitution takes account of whether the current value is a scalar or an array, whether the whole substitution is in double quotes, and what flags are supplied to the current level of substitution, just as if the nested substitution were the outermost. The flags are not propagated up to enclosing substitutions; the nested substitution will return either a scalar or an array as determined by the flags, possibly adjusted for quoting. All the following steps take place where applicable at all levels of substitution. Note that, unless the '(P)' flag is present, the flags and any subscripts apply directly to the value of the nested substitution; for example, the expansion ${${foo}} behaves exactly the same as ${foo}. When the '(P)' flag is present in a nested substitution, the other substitution rules are applied to the value _before_ it is interpreted as a name, so ${${(P)foo}} may differ from ${(P)foo}. At each nested level of substitution, the substituted words undergo all forms of single-word substitution (i.e. not filename generation), including command substitution, arithmetic expansion and filename expansion (i.e. leading ~ and =). Thus, for example, ${${:-=cat}:h} expands to the directory where the cat program resides. (Explanation: the internal substitution has no parameter but a default value =cat, which is expanded by filename expansion to a full path; the outer substitution then applies the modifier :h and takes the directory part of the path.) 2. _Internal parameter flags_ Any parameter flags set by one of the typeset family of commands, in particular the -L, -R, -Z, -u and -l options for padding and capitalization, are applied directly to the parameter value. Note these flags are options to the command, e.g. 'typeset -Z'; they are not the same as the flags used within parameter substitutions. At the outermost level of substitution, the '(P)' flag (rule 4.) ignores these transformations and uses the unmodified value of the parameter as the name to be replaced. This is usually the desired behavior because padding may make the value syntactically illegal as a parameter name, but if capitalization changes are desired, use the ${${(P)foo}} form (rule 25.). 3. _Parameter subscripting_ If the value is a raw parameter reference with a subscript, such as ${VAR[3]}, the effect of subscripting is applied directly to the parameter. Subscripts are evaluated left to right; subsequent subscripts apply to the scalar or array value yielded by the previous subscript. Thus if var is an array, ${var[1][2]} is the second character of the first word, but ${var[2,4][2]} is the entire third word (the second word of the range of words two through four of the original array). Any number of subscripts may appear. Flags such as '(k)' and '(v)' which alter the result of subscripting are applied. 4. _Parameter name replacement_ At the outermost level of nesting only, the '(P)' flag is applied. This treats the value so far as a parameter name (which may include a subscript expression) and replaces that with the corresponding value. This replacement occurs later if the '(P)' flag appears in a nested substitution. If the value so far names a parameter that has internal flags (rule 2.), those internal flags are applied to the new value after replacement. 5. _Double-quoted joining_ If the value after this process is an array, and the substitution appears in double quotes, and neither an '(@)' flag nor a '#' length operator is present at the current level, then words of the value are joined with the first character of the parameter $IFS, by default a space, between each word (single word arrays are not modified). If the '(j)' flag is present, that is used for joining instead of $IFS. 6. _Nested subscripting_ Any remaining subscripts (i.e. of a nested substitution) are evaluated at this point, based on whether the value is an array or a scalar. As with 3., multiple subscripts can appear. Note that ${foo[2,4][2]} is thus equivalent to ${${foo[2,4]}[2]} and also to "${${(@)foo[2,4]}[2]}" (the nested substitution returns an array in both cases), but not to "${${foo[2,4]}[2]}" (the nested substitution returns a scalar because of the quotes). 7. _Modifiers_ Any modifiers, as specified by a trailing '#', '%', '/' (possibly doubled) or by a set of modifiers of the form ':...' (see *note Modifiers:: in *note History Expansion::), are applied to the words of the value at this level. 8. _Character evaluation_ Any '(#)' flag is applied, evaluating the result so far numerically as a character. 9. _Length_ Any initial '#' modifier, i.e. in the form ${#VAR}, is used to evaluate the length of the expression so far. 10. _Forced joining_ If the '(j)' flag is present, or no '(j)' flag is present but the string is to be split as given by rule 11., and joining did not take place at rule 5., any words in the value are joined together using the given string or the first character of $IFS if none. Note that the '(F)' flag implicitly supplies a string for joining in this manner. 11. _Simple word splitting_ If one of the '(s)' or '(f)' flags are present, or the '=' specifier was present (e.g. ${=VAR}), the word is split on occurrences of the specified string, or (for = with neither of the two flags present) any of the characters in $IFS. If no '(s)', '(f)' or '=' was given, but the word is not quoted and the option SH_WORD_SPLIT is set, the word is split on occurrences of any of the characters in $IFS. Note this step, too, takes place at all levels of a nested substitution. 12. _Case modification_ Any case modification from one of the flags '(L)', '(U)' or '(C)' is applied. 13. _Escape sequence replacement_ First any replacements from the '(g)' flag are performed, then any prompt-style formatting from the '(%)' family of flags is applied. 14. _Quote application_ Any quoting or unquoting using '(q)' and '(Q)' and related flags is applied. 15. _Directory naming_ Any directory name substitution using '(D)' flag is applied. 16. _Visibility enhancement_ Any modifications to make characters visible using the '(V)' flag are applied. 17. _Lexical word splitting_ If the '(z)' flag or one of the forms of the '(Z)' flag is present, the word is split as if it were a shell command line, so that quotation marks and other metacharacters are used to decide what constitutes a word. Note this form of splitting is entirely distinct from that described by rule 11.: it does not use $IFS, and does not cause forced joining. 18. _Uniqueness_ If the result is an array and the '(u)' flag was present, duplicate elements are removed from the array. 19. _Ordering_ If the result is still an array and one of the '(o)' or '(O)' flags was present, the array is reordered. 20. RC_EXPAND_PARAM At this point the decision is made whether any resulting array elements are to be combined element by element with surrounding text, as given by either the RC_EXPAND_PARAM option or the '^' flag. 21. _Re-evaluation_ Any '(e)' flag is applied to the value, forcing it to be re-examined for new parameter substitutions, but also for command and arithmetic substitutions. 22. _Padding_ Any padding of the value by the '(l.FILL.)' or '(r.FILL.)' flags is applied. 23. _Semantic joining_ In contexts where expansion semantics requires a single word to result, all words are rejoined with the first character of IFS between. So in '${(P)${(f)lines}}' the value of ${lines} is split at newlines, but then must be joined again before the '(P)' flag can be applied. If a single word is not required, this rule is skipped. 24. _Empty argument removal_ If the substitution does not appear in double quotes, any resulting zero-length argument, whether from a scalar or an element of an array, is elided from the list of arguments inserted into the command line. Strictly speaking, the removal happens later as the same happens with other forms of substitution; the point to note here is simply that it occurs after any of the above parameter operations. 25. _Nested parameter name replacement_ If the '(P)' flag is present and rule 4. has not applied, the value so far is treated as a parameter name (which may include a subscript expression) and replaced with the corresponding value, with internal flags (rule 2.) applied to the new value. 14.3.3 Examples --------------- The flag f is useful to split a double-quoted substitution line by line. For example, ${(f)"$( Matches any number in the range X to Y, inclusive. Either of the numbers may be omitted to make the range open-ended; hence '<->' matches any number. To match individual digits, the [...] form is more efficient. Be careful when using other wildcards adjacent to patterns of this form; for example, <0-9>* will actually match any number whatsoever at the start of the string, since the '<0-9>' will match the first digit, and the '*' will match any others. This is a trap for the unwary, but is in fact an inevitable consequence of the rule that the longest possible match always succeeds. Expressions such as '<0-9>[^[:digit:]]*' can be used instead. (...) Matches the enclosed pattern. This is used for grouping. If the KSH_GLOB option is set, then a '@', '*', '+', '?' or '!' immediately preceding the '(' is treated specially, as detailed below. The option SH_GLOB prevents bare parentheses from being used in this way, though the KSH_GLOB option is still available. Note that grouping cannot extend over multiple directories: it is an error to have a '/' within a group (this only applies for patterns used in filename generation). There is one exception: a group of the form (PAT/)# appearing as a complete path segment can match a sequence of directories. For example, foo/(a*/)#bar matches foo/bar, foo/any/bar, foo/any/anyother/bar, and so on. X|Y Matches either X or Y. This operator has lower precedence than any other. The '|' character must be within parentheses, to avoid interpretation as a pipeline. The alternatives are tried in order from left to right. ^X (Requires EXTENDED_GLOB to be set.) Matches anything except the pattern X. This has a higher precedence than '/', so '^foo/bar' will search directories in '.' except './foo' for a file named 'bar'. X~Y (Requires EXTENDED_GLOB to be set.) Match anything that matches the pattern X but does not match Y. This has lower precedence than any operator except '|', so '*/*~foo/bar' will search for all files in all directories in '.' and then exclude 'foo/bar' if there was such a match. Multiple patterns can be excluded by 'FOO~BAR~BAZ'. In the exclusion pattern (Y), '/' and '.' are not treated specially the way they usually are in globbing. X# (Requires EXTENDED_GLOB to be set.) Matches zero or more occurrences of the pattern X. This operator has high precedence; '12#' is equivalent to '1(2#)', rather than '(12)#'. It is an error for an unquoted '#' to follow something which cannot be repeated; this includes an empty string, a pattern already followed by '##', or parentheses when part of a KSH_GLOB pattern (for example, '!(FOO)#' is invalid and must be replaced by '*(!(FOO))'). X## (Requires EXTENDED_GLOB to be set.) Matches one or more occurrences of the pattern X. This operator has high precedence; '12##' is equivalent to '1(2##)', rather than '(12)##'. No more than two active '#' characters may appear together. (Note the potential clash with glob qualifiers in the form '1(2##)' which should therefore be avoided.) 14.8.2 ksh-like Glob Operators ------------------------------ If the KSH_GLOB option is set, the effects of parentheses can be modified by a preceding '@', '*', '+', '?' or '!'. This character need not be unquoted to have special effects, but the '(' must be. @(...) Match the pattern in the parentheses. (Like '(...)'.) *(...) Match any number of occurrences. (Like '(...)#', except that recursive directory searching is not supported.) +(...) Match at least one occurrence. (Like '(...)##', except that recursive directory searching is not supported.) ?(...) Match zero or one occurrence. (Like '(|...)'.) !(...) Match anything but the expression in parentheses. (Like '(^(...))'.) 14.8.3 Precedence ----------------- The precedence of the operators given above is (highest) '^', '/', '~', '|' (lowest); the remaining operators are simply treated from left to right as part of a string, with '#' and '##' applying to the shortest possible preceding unit (i.e. a character, '?', '[...]', '<...>', or a parenthesised expression). As mentioned above, a '/' used as a directory separator may not appear inside parentheses, while a '|' must do so; in patterns used in other contexts than filename generation (for example, in case statements and tests within '[[...]]'), a '/' is not special; and '/' is also not special after a '~' appearing outside parentheses in a filename pattern. 14.8.4 Globbing Flags --------------------- There are various flags which affect any text to their right up to the end of the enclosing group or to the end of the pattern; they require the EXTENDED_GLOB option. All take the form (#X) where X may have one of the following forms: i Case insensitive: upper or lower case characters in the pattern match upper or lower case characters. l Lower case characters in the pattern match upper or lower case characters; upper case characters in the pattern still only match upper case characters. I Case sensitive: locally negates the effect of i or l from that point on. b Activate backreferences for parenthesised groups in the pattern; this does not work in filename generation. When a pattern with a set of active parentheses is matched, the strings matched by the groups are stored in the array $match, the indices of the beginning of the matched parentheses in the array $mbegin, and the indices of the end in the array $mend, with the first element of each array corresponding to the first parenthesised group, and so on. These arrays are not otherwise special to the shell. The indices use the same convention as does parameter substitution, so that elements of $mend and $mbegin may be used in subscripts; the KSH_ARRAYS option is respected. Sets of globbing flags are not considered parenthesised groups; only the first nine active parentheses can be referenced. For example, foo="a_string_with_a_message" if [[ $foo = (a|an)_(#b)(*) ]]; then print ${foo[$mbegin[1],$mend[1]]} fi prints 'string_with_a_message'. Note that the first set of parentheses is before the (#b) and does not create a backreference. Backreferences work with all forms of pattern matching other than filename generation, but note that when performing matches on an entire array, such as ${ARRAY#PATTERN}, or a global substitution, such as ${PARAM//PAT/REPL}, only the data for the last match remains available. In the case of global replacements this may still be useful. See the example for the m flag below. The numbering of backreferences strictly follows the order of the opening parentheses from left to right in the pattern string, although sets of parentheses may be nested. There are special rules for parentheses followed by '#' or '##'. Only the last match of the parenthesis is remembered: for example, in '[[ abab = (#b)([ab])# ]]', only the final 'b' is stored in match[1]. Thus extra parentheses may be necessary to match the complete segment: for example, use 'X((ab|cd)#)Y' to match a whole string of either 'ab' or 'cd' between 'X' and 'Y', using the value of $match[1] rather than $match[2]. If the match fails none of the parameters is altered, so in some cases it may be necessary to initialise them beforehand. If some of the backreferences fail to match -- which happens if they are in an alternate branch which fails to match, or if they are followed by # and matched zero times -- then the matched string is set to the empty string, and the start and end indices are set to -1. Pattern matching with backreferences is slightly slower than without. B Deactivate backreferences, negating the effect of the b flag from that point on. cN,M The flag (#cN,M) can be used anywhere that the # or ## operators can be used except in the expressions '(*/)#' and '(*/)##' in filename generation, where '/' has special meaning; it cannot be combined with other globbing flags and a bad pattern error occurs if it is misplaced. It is equivalent to the form {N,M} in regular expressions. The previous character or group is required to match between N and M times, inclusive. The form (#cN) requires exactly N matches; (#c,M) is equivalent to specifying N as 0; (#cN,) specifies that there is no maximum limit on the number of matches. m Set references to the match data for the entire string matched; this is similar to backreferencing and does not work in filename generation. The flag must be in effect at the end of the pattern, i.e. not local to a group. The parameters $MATCH, $MBEGIN and $MEND will be set to the string matched and to the indices of the beginning and end of the string, respectively. This is most useful in parameter substitutions, as otherwise the string matched is obvious. For example, arr=(veldt jynx grimps waqf zho buck) print ${arr//(#m)[aeiou]/${(U)MATCH}} forces all the matches (i.e. all vowels) into uppercase, printing 'vEldt jynx grImps wAqf zhO bUck'. Unlike backreferences, there is no speed penalty for using match references, other than the extra substitutions required for the replacement strings in cases such as the example shown. M Deactivate the m flag, hence no references to match data will be created. aNUM Approximate matching: NUM errors are allowed in the string matched by the pattern. The rules for this are described in the next subsection. s, e Unlike the other flags, these have only a local effect, and each must appear on its own: '(#s)' and '(#e)' are the only valid forms. The '(#s)' flag succeeds only at the start of the test string, and the '(#e)' flag succeeds only at the end of the test string; they correspond to '^' and '$' in standard regular expressions. They are useful for matching path segments in patterns other than those in filename generation (where path segments are in any case treated separately). For example, '*((#s)|/)test((#e)|/)*' matches a path segment 'test' in any of the following strings: test, test/at/start, at/end/test, in/test/middle. Another use is in parameter substitution; for example '${array/(#s)A*Z(#e)}' will remove only elements of an array which match the complete pattern 'A*Z'. There are other ways of performing many operations of this type, however the combination of the substitution operations '/' and '//' with the '(#s)' and '(#e)' flags provides a single simple and memorable method. Note that assertions of the form '(^(#s))' also work, i.e. match anywhere except at the start of the string, although this actually means 'anything except a zero-length portion at the start of the string'; you need to use '(""~(#s))' to match a zero-length portion of the string not at the start. q A 'q' and everything up to the closing parenthesis of the globbing flags are ignored by the pattern matching code. This is intended to support the use of glob qualifiers, see below. The result is that the pattern '(#b)(*).c(#q.)' can be used both for globbing and for matching against a string. In the former case, the '(#q.)' will be treated as a glob qualifier and the '(#b)' will not be useful, while in the latter case the '(#b)' is useful for backreferences and the '(#q.)' will be ignored. Note that colon modifiers in the glob qualifiers are also not applied in ordinary pattern matching. u Respect the current locale in determining the presence of multibyte characters in a pattern, provided the shell was compiled with MULTIBYTE_SUPPORT. This overrides the MULTIBYTE option; the default behaviour is taken from the option. Compare U. (Mnemonic: typically multibyte characters are from Unicode in the UTF-8 encoding, although any extension of ASCII supported by the system library may be used.) U All characters are considered to be a single byte long. The opposite of u. This overrides the MULTIBYTE option. For example, the test string fooxx can be matched by the pattern (#i)FOOXX, but not by (#l)FOOXX, (#i)FOO(#I)XX or ((#i)FOOX)X. The string (#ia2)readme specifies case-insensitive matching of readme with up to two errors. When using the ksh syntax for grouping both KSH_GLOB and EXTENDED_GLOB must be set and the left parenthesis should be preceded by @. Note also that the flags do not affect letters inside [...] groups, in other words (#i)[a-z] still matches only lowercase letters. Finally, note that when examining whole paths case-insensitively every directory must be searched for all files which match, so that a pattern of the form (#i)/foo/bar/... is potentially slow. 14.8.5 Approximate Matching --------------------------- When matching approximately, the shell keeps a count of the errors found, which cannot exceed the number specified in the (#aNUM) flags. Four types of error are recognised: 1. Different characters, as in fooxbar and fooybar. 2. Transposition of characters, as in banana and abnana. 3. A character missing in the target string, as with the pattern road and target string rod. 4. An extra character appearing in the target string, as with stove and strove. Thus, the pattern (#a3)abcd matches dcba, with the errors occurring by using the first rule twice and the second once, grouping the string as [d][cb][a] and [a][bc][d]. Non-literal parts of the pattern must match exactly, including characters in character ranges: hence (#a1)??? matches strings of length four, by applying rule 4 to an empty part of the pattern, but not strings of length two, since all the ? must match. Other characters which must match exactly are initial dots in filenames (unless the GLOB_DOTS option is set), and all slashes in filenames, so that a/bc is two errors from ab/c (the slash cannot be transposed with another character). Similarly, errors are counted separately for non-contiguous strings in the pattern, so that (ab|cd)ef is two errors from aebf. When using exclusion via the ~ operator, approximate matching is treated entirely separately for the excluded part and must be activated separately. Thus, (#a1)README~READ_ME matches READ.ME but not READ_ME, as the trailing READ_ME is matched without approximation. However, (#a1)README~(#a1)READ_ME does not match any pattern of the form READ?ME as all such forms are now excluded. Apart from exclusions, there is only one overall error count; however, the maximum errors allowed may be altered locally, and this can be delimited by grouping. For example, (#a1)cat((#a0)dog)fox allows one error in total, which may not occur in the dog section, and the pattern (#a1)cat(#a0)dog(#a1)fox is equivalent. Note that the point at which an error is first found is the crucial one for establishing whether to use approximation; for example, (#a1)abc(#a0)xyz will not match abcdxyz, because the error occurs at the 'x', where approximation is turned off. Entire path segments may be matched approximately, so that '(#a1)/foo/d/is/available/at/the/bar' allows one error in any path segment. This is much less efficient than without the (#a1), however, since every directory in the path must be scanned for a possible approximate match. It is best to place the (#a1) after any path segments which are known to be correct. 14.8.6 Recursive Globbing ------------------------- A pathname component of the form '(FOO/)#' matches a path consisting of zero or more directories matching the pattern FOO. As a shorthand, '**/' is equivalent to '(*/)#'; note that this therefore matches files in the current directory as well as subdirectories. Thus: ls -ld -- (*/)#bar or ls -ld -- **/bar does a recursive directory search for files named 'bar' (potentially including the file 'bar' in the current directory). This form does not follow symbolic links; the alternative form '***/' does, but is otherwise identical. Neither of these can be combined with other forms of globbing within the same path segment; in that case, the '*' operators revert to their usual effect. Even shorter forms are available when the option GLOB_STAR_SHORT is set. In that case if no / immediately follows a ** or *** they are treated as if both a / plus a further * are present. Hence: setopt GLOBSTARSHORT ls -ld -- **.c is equivalent to ls -ld -- **/*.c 14.8.7 Glob Qualifiers ---------------------- Patterns used for filename generation may end in a list of qualifiers enclosed in parentheses. The qualifiers specify which filenames that otherwise match the given pattern will be inserted in the argument list. If the option BARE_GLOB_QUAL is set, then a trailing set of parentheses containing no '|' or '(' characters (or '~' if it is special) is taken as a set of glob qualifiers. A glob subexpression that would normally be taken as glob qualifiers, for example '(^x)', can be forced to be treated as part of the glob pattern by doubling the parentheses, in this case producing '((^x))'. If the option EXTENDED_GLOB is set, a different syntax for glob qualifiers is available, namely '(#qX)' where X is any of the same glob qualifiers used in the other format. The qualifiers must still appear at the end of the pattern. However, with this syntax multiple glob qualifiers may be chained together. They are treated as a logical AND of the individual sets of flags. Also, as the syntax is unambiguous, the expression will be treated as glob qualifiers just as long any parentheses contained within it are balanced; appearance of '|', '(' or '~' does not negate the effect. Note that qualifiers will be recognised in this form even if a bare glob qualifier exists at the end of the pattern, for example '*(#q*)(.)' will recognise executable regular files if both options are set; however, mixed syntax should probably be avoided for the sake of clarity. Note that within conditions using the '[[' form the presence of a parenthesised expression (#q...) at the end of a string indicates that globbing should be performed; the expression may include glob qualifiers, but it is also valid if it is simply (#q). This does not apply to the right hand side of pattern match operators as the syntax already has special significance. A qualifier may be any one of the following: / directories F 'full' (i.e. non-empty) directories. Note that the opposite sense (^F) expands to empty directories and all non-directories. Use (/^F) for empty directories. . plain files @ symbolic links = sockets p named pipes (FIFOs) * executable plain files (0100 or 0010 or 0001) % device files (character or block special) %b block special files %c character special files r owner-readable files (0400) w owner-writable files (0200) x owner-executable files (0100) A group-readable files (0040) I group-writable files (0020) E group-executable files (0010) R world-readable files (0004) W world-writable files (0002) X world-executable files (0001) s setuid files (04000) S setgid files (02000) t files with the sticky bit (01000) fSPEC files with access rights matching SPEC. This SPEC may be a octal number optionally preceded by a '=', a '+', or a '-'. If none of these characters is given, the behavior is the same as for '='. The octal number describes the mode bits to be expected, if combined with a '=', the value given must match the file-modes exactly, with a '+', at least the bits in the given number must be set in the file-modes, and with a '-', the bits in the number must not be set. Giving a '?' instead of a octal digit anywhere in the number ensures that the corresponding bits in the file-modes are not checked, this is only useful in combination with '='. If the qualifier 'f' is followed by any other character anything up to the next matching character ('[', '{', and '<' match ']', '}', and '>' respectively, any other character matches itself) is taken as a list of comma-separated SUB-SPECs. Each SUB-SPEC may be either an octal number as described above or a list of any of the characters 'u', 'g', 'o', and 'a', followed by a '=', a '+', or a '-', followed by a list of any of the characters 'r', 'w', 'x', 's', and 't', or an octal digit. The first list of characters specify which access rights are to be checked. If a 'u' is given, those for the owner of the file are used, if a 'g' is given, those of the group are checked, a 'o' means to test those of other users, and the 'a' says to test all three groups. The '=', '+', and '-' again says how the modes are to be checked and have the same meaning as described for the first form above. The second list of characters finally says which access rights are to be expected: 'r' for read access, 'w' for write access, 'x' for the right to execute the file (or to search a directory), 's' for the setuid and setgid bits, and 't' for the sticky bit. Thus, '*(f70?)' gives the files for which the owner has read, write, and execute permission, and for which other group members have no rights, independent of the permissions for other users. The pattern '*(f-100)' gives all files for which the owner does not have execute permission, and '*(f:gu+w,o-rx:)' gives the files for which the owner and the other members of the group have at least write permission, and for which other users don't have read or execute permission. eSTRING +CMD The STRING will be executed as shell code. The filename will be included in the list if and only if the code returns a zero status (usually the status of the last command). In the first form, the first character after the 'e' will be used as a separator and anything up to the next matching separator will be taken as the STRING; '[', '{', and '<' match ']', '}', and '>', respectively, while any other character matches itself. Note that expansions must be quoted in the STRING to prevent them from being expanded before globbing is done. STRING is then executed as shell code. The string globqual is appended to the array zsh_eval_context the duration of execution. During the execution of STRING the filename currently being tested is available in the parameter REPLY; the parameter may be altered to a string to be inserted into the list instead of the original filename. In addition, the parameter reply may be set to an array or a string, which overrides the value of REPLY. If set to an array, the latter is inserted into the command line word by word. For example, suppose a directory contains a single file 'lonely'. Then the expression '*(e:'reply=(${REPLY}{1,2})':)' will cause the words 'lonely1' and 'lonely2' to be inserted into the command line. Note the quoting of STRING. The form +CMD has the same effect, but no delimiters appear around CMD. Instead, CMD is taken as the longest sequence of characters following the + that are alphanumeric or underscore. Typically CMD will be the name of a shell function that contains the appropriate test. For example, nt() { [[ $REPLY -nt $NTREF ]] } NTREF=reffile ls -ld -- *(+nt) lists all files in the directory that have been modified more recently than reffile. dDEV files on the device DEV l[-|+]CT files having a link count less than CT (-), greater than CT (+), or equal to CT U files owned by the effective user ID G files owned by the effective group ID uID files owned by user ID ID if that is a number. Otherwise, ID specifies a user name: the character after the 'u' will be taken as a separator and the string between it and the next matching separator will be taken as a user name. The starting separators '[', '{', and '<' match the final separators ']', '}', and '>', respectively; any other character matches itself. The selected files are those owned by this user. For example, 'u:foo:' or 'u[foo]' selects files owned by user 'foo'. gID like uID but with group IDs or names a[Mwhms][-|+]N files accessed exactly N days ago. Files accessed within the last N days are selected using a negative value for N (-N). Files accessed more than N days ago are selected by a positive N value (+N). Optional unit specifiers 'M', 'w', 'h', 'm' or 's' (e.g. 'ah5') cause the check to be performed with months (of 30 days), weeks, hours, minutes or seconds instead of days, respectively. An explicit 'd' for days is also allowed. Any fractional part of the difference between the access time and the current part in the appropriate units is ignored in the comparison. For instance, 'echo *(ah-5)' would echo files accessed within the last five hours, while 'echo *(ah+5)' would echo files accessed at least six hours ago, as times strictly between five and six hours are treated as five hours. m[Mwhms][-|+]N like the file access qualifier, except that it uses the file modification time. c[Mwhms][-|+]N like the file access qualifier, except that it uses the file inode change time. L[+|-]N files less than N bytes (-), more than N bytes (+), or exactly N bytes in length. If this flag is directly followed by a _size specifier_ 'k' ('K'), 'm' ('M'), or 'p' ('P') (e.g. 'Lk-50') the check is performed with kilobytes, megabytes, or blocks (of 512 bytes) instead. (On some systems additional specifiers are available for gigabytes, 'g' or 'G', and terabytes, 't' or 'T'.) If a size specifier is used a file is regarded as "exactly" the size if the file size rounded up to the next unit is equal to the test size. Hence '*(Lm1)' matches files from 1 byte up to 1 Megabyte inclusive. Note also that the set of files "less than" the test size only includes files that would not match the equality test; hence '*(Lm-1)' only matches files of zero size. ^ negates all qualifiers following it - toggles between making the qualifiers work on symbolic links (the default) and the files they point to, if any; any symbolic link for whose target the 'stat' system call fails (whatever the cause of the failure) is treated as a file in its own right M sets the MARK_DIRS option for the current pattern T appends a trailing qualifier mark to the filenames, analogous to the LIST_TYPES option, for the current pattern (overrides M) N sets the NULL_GLOB option for the current pattern D sets the GLOB_DOTS option for the current pattern n sets the NUMERIC_GLOB_SORT option for the current pattern YN enables short-circuit mode: the pattern will expand to at most N filenames. If more than N matches exist, only the first N matches in directory traversal order will be considered. Implies oN when no oC qualifier is used. oC specifies how the names of the files should be sorted. The following values of C sort in the following ways: n By name. L By the size (length) of the files. l By number of links. a By time of last access, youngest first. m By time of last modification, youngest first. c By time of last inode change, youngest first. d By directories: files in subdirectories appear before those in the current directory at each level of the search -- this is best combined with other criteria, for example 'odon' to sort on names for files within the same directory. N No sorting is performed. eSTRING +CMD Sort by shell code (see below). Note that the modifiers ^ and - are used, so '*(^-oL)' gives a list of all files sorted by file size in descending order, following any symbolic links. Unless oN is used, multiple order specifiers may occur to resolve ties. The default sorting is n (by name) unless the Y glob qualifier is used, in which case it is N (unsorted). oe and o+ are special cases; they are each followed by shell code, delimited as for the e glob qualifier and the + glob qualifier respectively (see above). The code is executed for each matched file with the parameter REPLY set to the name of the file on entry and globsort appended to zsh_eval_context. The code should modify the parameter REPLY in some fashion. On return, the value of the parameter is used instead of the file name as the string on which to sort. Unlike other sort operators, oe and o+ may be repeated, but note that the maximum number of sort operators of any kind that may appear in any glob expression is 12. OC like 'o', but sorts in descending order; i.e. '*(^oC)' is the same as '*(OC)' and '*(^OC)' is the same as '*(oC)'; 'Od' puts files in the current directory before those in subdirectories at each level of the search. [BEG[,END]] specifies which of the matched filenames should be included in the returned list. The syntax is the same as for array subscripts. BEG and the optional END may be mathematical expressions. As in parameter subscripting they may be negative to make them count from the last match backward. E.g.: '*(-OL[1,3])' gives a list of the names of the three largest files. PSTRING The STRING will be prepended to each glob match as a separate word. STRING is delimited in the same way as arguments to the e glob qualifier described above. The qualifier can be repeated; the words are prepended separately so that the resulting command line contains the words in the same order they were given in the list of glob qualifiers. A typical use for this is to prepend an option before all occurrences of a file name; for example, the pattern '*(P:-f:)' produces the command line arguments '-f FILE1 -f FILE2 ...' If the modifier ^ is active, then STRING will be appended instead of prepended. Prepending and appending is done independently so both can be used on the same glob expression; for example by writing '*(P:foo:^P:bar:^P:baz:)' which produces the command line arguments 'foo baz FILE1 bar ...' More than one of these lists can be combined, separated by commas. The whole list matches if at least one of the sublists matches (they are 'or'ed, the qualifiers in the sublists are 'and'ed). Some qualifiers, however, affect all matches generated, independent of the sublist in which they are given. These are the qualifiers 'M', 'T', 'N', 'D', 'n', 'o', 'O' and the subscripts given in brackets ('[...]'). If a ':' appears in a qualifier list, the remainder of the expression in parenthesis is interpreted as a modifier (see *note Modifiers:: in *note History Expansion::). Each modifier must be introduced by a separate ':'. Note also that the result after modification does not have to be an existing file. The name of any existing file can be followed by a modifier of the form '(:...)' even if no actual filename generation is performed, although note that the presence of the parentheses causes the entire expression to be subjected to any global pattern matching options such as NULL_GLOB. Thus: ls -ld -- *(-/) lists all directories and symbolic links that point to directories, and ls -ld -- *(-@) lists all broken symbolic links, and ls -ld -- *(%W) lists all world-writable device files in the current directory, and ls -ld -- *(W,X) lists all files in the current directory that are world-writable or world-executable, and print -rC1 /tmp/foo*(u0^@:t) outputs the basename of all root-owned files beginning with the string 'foo' in /tmp, ignoring symlinks, and ls -ld -- *.*~(lex|parse).[ch](^D^l1) lists all files having a link count of one whose names contain a dot (but not those starting with a dot, since GLOB_DOTS is explicitly switched off) except for lex.c, lex.h, parse.c and parse.h. print -rC1 b*.pro(#q:s/pro/shmo/)(#q.:s/builtin/shmiltin/) demonstrates how colon modifiers and other qualifiers may be chained together. The ordinary qualifier '.' is applied first, then the colon modifiers in order from left to right. So if EXTENDED_GLOB is set and the base pattern matches the regular file builtin.pro, the shell will print 'shmiltin.shmo'.  File: zsh.info, Node: Parameters, Next: Options, Prev: Expansion, Up: Top 15 Parameters ************* 15.1 Description ================ A parameter has a name, a value, and a number of attributes. A name may be any sequence of alphanumeric characters and underscores, or the single characters '*', '@', '#', '?', '-', '$', or '!'. A parameter whose name begins with an alphanumeric or underscore is also referred to as a _variable_. The attributes of a parameter determine the _type_ of its value, often referred to as the parameter type or variable type, and also control other processing that may be applied to the value when it is referenced. The value type may be a _scalar_ (a string, an integer, or a floating point number), an array (indexed numerically), or an _associative_ array (an unordered set of name-value pairs, indexed by name, also referred to as a _hash_). Named scalar parameters may have the _exported_, -x, attribute, to copy them into the process environment, which is then passed from the shell to any new processes that it starts. Exported parameters are called _environment variables_. The shell also _imports_ environment variables at startup time and automatically marks the corresponding parameters as exported. Some environment variables are not imported for reasons of security or because they would interfere with the correct operation of other shell features. Parameters may also be _special_, that is, they have a predetermined meaning to the shell. Special parameters cannot have their type changed or their readonly attribute turned off, and if a special parameter is unset, then later recreated, the special properties will be retained. To declare the type of a parameter, or to assign a string or numeric value to a scalar parameter, use the typeset builtin. The value of a scalar parameter may also be assigned by writing: NAME=VALUE In scalar assignment, VALUE is expanded as a single string, in which the elements of arrays are joined together; filename expansion is not performed unless the option GLOB_ASSIGN is set. When the integer attribute, -i, or a floating point attribute, -E or -F, is set for NAME, the VALUE is subject to arithmetic evaluation. Furthermore, by replacing '=' with '+=', a parameter can be incremented or appended to. See *note Array Parameters:: and *note Arithmetic Evaluation:: for additional forms of assignment. Note that assignment may implicitly change the attributes of a parameter. For example, assigning a number to a variable in arithmetic evaluation may change its type to integer or float, and with GLOB_ASSIGN assigning a pattern to a variable may change its type to an array. To reference the value of a parameter, write '$NAME' or '${NAME}'. See *note Parameter Expansion:: for complete details. That section also explains the effect of the difference between scalar and array assignment on parameter expansion. * Menu: * Array Parameters:: * Positional Parameters:: * Local Parameters:: * Parameters Set By The Shell:: * Parameters Used By The Shell::  File: zsh.info, Node: Array Parameters, Next: Positional Parameters, Up: Parameters 15.2 Array Parameters ===================== To assign an array value, write one of: set -A NAME VALUE ... NAME=(VALUE ...) NAME=([KEY]=VALUE ...) If no parameter NAME exists, an ordinary array parameter is created. If the parameter NAME exists and is a scalar, it is replaced by a new array. In the third form, KEY is an expression that will be evaluated in arithmetic context (in its simplest form, an integer) that gives the index of the element to be assigned with VALUE. In this form any elements not explicitly mentioned that come before the largest index to which a value is assigned are assigned an empty string. The indices may be in any order. Note that this syntax is strict: [ and ]= must not be quoted, and KEY may not consist of the unquoted string ]=, but is otherwise treated as a simple string. The enhanced forms of subscript expression that may be used when directly subscripting a variable name, described in the section 'Array Subscripts' below, are not available. The syntaxes with and without the explicit key may be mixed. An implicit KEY is deduced by incrementing the index from the previously assigned element. Note that it is not treated as an error if latter assignments in this form overwrite earlier assignments. For example, assuming the option KSH_ARRAYS is not set, the following: array=(one [3]=three four) causes the array variable array to contain four elements one, an empty string, three and four, in that order. In the forms where only VALUE is specified, full command line expansion is performed. In the [KEY]=VALUE form, both KEY and VALUE undergo all forms of expansion allowed for single word shell expansions (this does not include filename generation); these are as performed by the parameter expansion flag (e) as described in *note Parameter Expansion::. Nested parentheses may surround VALUE and are included as part of the value, which is joined into a plain string; this differs from ksh which allows the values themselves to be arrays. A future version of zsh may support that. To cause the brackets to be interpreted as a character class for filename generation, and therefore to treat the resulting list of files as a set of values, quote the equal sign using any form of quoting. Example: NAME=([a-z]'='*) To append to an array without changing the existing values, use one of the following: NAME+=(VALUE ...) NAME+=([KEY]=VALUE ...) In the second form KEY may specify an existing index as well as an index off the end of the old array; any existing value is overwritten by VALUE. Also, it is possible to use [KEY]+=VALUE to append to the existing value at that index. Within the parentheses on the right hand side of either form of the assignment, newlines and semicolons are treated the same as white space, separating individual VALUEs. Any consecutive sequence of such characters has the same effect. Ordinary array parameters may also be explicitly declared with: typeset -a NAME Associative arrays _must_ be declared before assignment, by using: typeset -A NAME When NAME refers to an associative array, the list in an assignment is interpreted as alternating keys and values: set -A NAME KEY VALUE ... NAME=(KEY VALUE ...) NAME=([KEY]=VALUE ...) Note that only one of the two syntaxes above may be used in any given assignment; the forms may not be mixed. This is unlike the case of numerically indexed arrays. Every KEY must have a VALUE in this case. Note that this assigns to the entire array, deleting any elements that do not appear in the list. The append syntax may also be used with an associative array: NAME+=(KEY VALUE ...) NAME+=([KEY]=VALUE ...) This adds a new key/value pair if the key is not already present, and replaces the value for the existing key if it is. In the second form it is also possible to use [KEY]+=VALUE to append to the existing value at that key. Expansion is performed identically to the corresponding forms for normal arrays, as described above. To create an empty array (including associative arrays), use one of: set -A NAME NAME=() 15.2.1 Array Subscripts ----------------------- Individual elements of an array may be selected using a subscript. A subscript of the form '[EXP]' selects the single element EXP, where EXP is an arithmetic expression which will be subject to arithmetic expansion as if it were surrounded by '$((...))'. The elements are numbered beginning with 1, unless the KSH_ARRAYS option is set in which case they are numbered from zero. Subscripts may be used inside braces used to delimit a parameter name, thus '${foo[2]}' is equivalent to '$foo[2]'. If the KSH_ARRAYS option is set, the braced form is the only one that works, as bracketed expressions otherwise are not treated as subscripts. If the KSH_ARRAYS option is not set, then by default accesses to an array element with a subscript that evaluates to zero return an empty string, while an attempt to write such an element is treated as an error. For backward compatibility the KSH_ZERO_SUBSCRIPT option can be set to cause subscript values 0 and 1 to be equivalent; see the description of the option in *note Description of Options::. The same subscripting syntax is used for associative arrays, except that no arithmetic expansion is applied to EXP. However, the parsing rules for arithmetic expressions still apply, which affects the way that certain special characters must be protected from interpretation. See _Subscript Parsing_ below for details. A subscript of the form '[*]' or '[@]' evaluates to all elements of an array; there is no difference between the two except when they appear within double quotes. '"$foo[*]"' evaluates to '"$foo[1] $foo[2] ..."', whereas '"$foo[@]"' evaluates to '"$foo[1]" "$foo[2]" ...'. For associative arrays, '[*]' or '[@]' evaluate to all the values, in no particular order. Note that this does not substitute the keys; see the documentation for the 'k' flag under *note Parameter Expansion:: for complete details. When an array parameter is referenced as '$NAME' (with no subscript) it evaluates to '$NAME[*]', unless the KSH_ARRAYS option is set in which case it evaluates to '${NAME[0]}' (for an associative array, this means the value of the key '0', which may not exist even if there are values for other keys). A subscript of the form '[EXP1,EXP2]' selects all elements in the range EXP1 to EXP2, inclusive. (Associative arrays are unordered, and so do not support ranges.) If one of the subscripts evaluates to a negative number, say -N, then the Nth element from the end of the array is used. Thus '$foo[-3]' is the third element from the end of the array foo, and '$foo[1,-1]' is the same as '$foo[*]'. Subscripting may also be performed on non-array values, in which case the subscripts specify a substring to be extracted. For example, if FOO is set to 'foobar', then 'echo $FOO[2,5]' prints 'ooba'. Note that some forms of subscripting described below perform pattern matching, and in that case the substring extends from the start of the match of the first subscript to the end of the match of the second subscript. For example, string="abcdefghijklm" print ${string[(r)d?,(r)h?]} prints 'defghi'. This is an obvious generalisation of the rule for single-character matches. For a single subscript, only a single character is referenced (not the range of characters covered by the match). Note that in substring operations the second subscript is handled differently by the r and R subscript flags: the former takes the shortest match as the length and the latter the longest match. Hence in the former case a * at the end is redundant while in the latter case it matches the whole remainder of the string. This does not affect the result of the single subscript case as here the length of the match is irrelevant. 15.2.2 Array Element Assignment ------------------------------- A subscript may be used on the left side of an assignment like so: NAME[EXP]=VALUE In this form of assignment the element or range specified by EXP is replaced by the expression on the right side. An array (but not an associative array) may be created by assignment to a range or element. Arrays do not nest, so assigning a parenthesized list of values to an element or range changes the number of elements in the array, shifting the other elements to accommodate the new values. (This is not supported for associative arrays.) This syntax also works as an argument to the typeset command: typeset "NAME[EXP]"=VALUE The VALUE may _not_ be a parenthesized list in this case; only single-element assignments may be made with typeset. Note that quotes are necessary in this case to prevent the brackets from being interpreted as filename generation operators. The noglob precommand modifier could be used instead. To delete an element of an ordinary array, assign '()' to that element. To delete an element of an associative array, use the unset command: unset "NAME[EXP]" 15.2.3 Subscript Flags ---------------------- If the opening bracket, or the comma in a range, in any subscript expression is directly followed by an opening parenthesis, the string up to the matching closing one is considered to be a list of flags, as in 'NAME[(FLAGS)EXP]'. The flags s, n and b take an argument; the delimiter is shown below as ':', but any character, or the matching pairs '(...)', '{...}', '[...]', or '<...>', may be used, but note that '<...>' can only be used if the subscript is inside a double quoted expression or a parameter substitution enclosed in braces as otherwise the expression is interpreted as a redirection. The flags currently understood are: w If the parameter subscripted is a scalar then this flag makes subscripting work on words instead of characters. The default word separator is whitespace. When combined with the i or I flag, the effect is to produce the index of the first character of the first/last word which matches the given pattern; note that a failed match in this case always yields 0. s:STRING: This gives the STRING that separates words (for use with the w flag). The delimiter character : is arbitrary; see above. p Recognize the same escape sequences as the print builtin in the string argument of a subsequent 's' flag. f If the parameter subscripted is a scalar then this flag makes subscripting work on lines instead of characters, i.e. with elements separated by newlines. This is a shorthand for 'pws:\n:'. r Reverse subscripting: if this flag is given, the EXP is taken as a pattern and the result is the first matching array element, substring or word (if the parameter is an array, if it is a scalar, or if it is a scalar and the 'w' flag is given, respectively). The subscript used is the number of the matching element, so that pairs of subscripts such as '$foo[(r)??,3]' and '$foo[(r)??,(r)f*]' are possible if the parameter is not an associative array. If the parameter is an associative array, only the value part of each pair is compared to the pattern, and the result is that value. If a search through an ordinary array failed, the search sets the subscript to one past the end of the array, and hence ${array[(r)PATTERN]} will substitute the empty string. Thus the success of a search can be tested by using the (i) flag, for example (assuming the option KSH_ARRAYS is not in effect): [[ ${array[(i)pattern]} -le ${#array} ]] If KSH_ARRAYS is in effect, the -le should be replaced by -lt. R Like 'r', but gives the last match. For associative arrays, gives all possible matches. May be used for assigning to ordinary array elements, but not for assigning to associative arrays. On failure, for normal arrays this has the effect of returning the element corresponding to subscript 0; this is empty unless one of the options KSH_ARRAYS or KSH_ZERO_SUBSCRIPT is in effect. Note that in subscripts with both 'r' and 'R' pattern characters are active even if they were substituted for a parameter (regardless of the setting of GLOB_SUBST which controls this feature in normal pattern matching). The flag 'e' can be added to inhibit pattern matching. As this flag does not inhibit other forms of substitution, care is still required; using a parameter to hold the key has the desired effect: key2='original key' print ${array[(Re)$key2]} i Like 'r', but gives the index of the match instead; this may not be combined with a second argument. On the left side of an assignment, behaves like 'r'. For associative arrays, the key part of each pair is compared to the pattern, and the first matching key found is the result. On failure substitutes the length of the array plus one, as discussed under the description of 'r', or the empty string for an associative array. Note: Although 'i' may be applied to a scalar substitution to find the offset of a substring, the results are likely to be misleading when searching within substitutions that yield an empty string, or when searching for the empty substring. I Like 'i', but gives the index of the last match, or all possible matching keys in an associative array. On failure substitutes 0, or the empty string for an associative array. This flag is best when testing for values or keys that do not exist. Note: If the option KSH_ARRAYS is in effect and no match is found, the result is indistinguishable from the case when the first element of the array matches. k If used in a subscript on an associative array, this flag causes the keys to be interpreted as patterns, and returns the value for the first key found where EXP is matched by the key. Note this could be any such key as no ordering of associative arrays is defined. This flag does not work on the left side of an assignment to an associative array element. If used on another type of parameter, this behaves like 'r'. K On an associative array this is like 'k' but returns all values where EXP is matched by the keys. On other types of parameters this has the same effect as 'R'. n:EXPR: If combined with 'r', 'R', 'i' or 'I', makes them give the Nth or Nth last match (if EXPR evaluates to N). This flag is ignored when the array is associative. The delimiter character : is arbitrary; see above. b:EXPR: If combined with 'r', 'R', 'i' or 'I', makes them begin at the Nth or Nth last element, word, or character (if EXPR evaluates to N). This flag is ignored when the array is associative. The delimiter character : is arbitrary; see above. e This flag causes any pattern matching that would be performed on the subscript to use plain string matching instead. Hence '${array[(re)*]}' matches only the array element whose value is *. Note that other forms of substitution such as parameter substitution are not inhibited. This flag can also be used to force * or @ to be interpreted as a single key rather than as a reference to all values. It may be used for either purpose on the left side of an assignment. See _Parameter Expansion Flags_ (*note Parameter Expansion::) for additional ways to manipulate the results of array subscripting. 15.2.4 Subscript Parsing ------------------------ This discussion applies mainly to associative array key strings and to patterns used for reverse subscripting (the 'r', 'R', 'i', etc. flags), but it may also affect parameter substitutions that appear as part of an arithmetic expression in an ordinary subscript. To avoid subscript parsing limitations in assignments to associative array elements, use the append syntax: aa+=('key with "*strange*" characters' 'value string') The basic rule to remember when writing a subscript expression is that all text between the opening '[' and the closing ']' is interpreted _as if_ it were in double quotes (*note Quoting::). However, unlike double quotes which normally cannot nest, subscript expressions may appear inside double-quoted strings or inside other subscript expressions (or both!), so the rules have two important differences. The first difference is that brackets ('[' and ']') must appear as balanced pairs in a subscript expression unless they are preceded by a backslash ('\'). Therefore, within a subscript expression (and unlike true double-quoting) the sequence '\[' becomes '[', and similarly '\]' becomes ']'. This applies even in cases where a backslash is not normally required; for example, the pattern '[^[]' (to match any character other than an open bracket) should be written '[^\[]' in a reverse-subscript pattern. However, note that '\[^\[\]' and even '\[^[]' mean the _same_ thing, because backslashes are always stripped when they appear before brackets! The same rule applies to parentheses ('(' and ')') and braces ('{' and '}'): they must appear either in balanced pairs or preceded by a backslash, and backslashes that protect parentheses or braces are removed during parsing. This is because parameter expansions may be surrounded by balanced braces, and subscript flags are introduced by balanced parentheses. The second difference is that a double-quote ('"') may appear as part of a subscript expression without being preceded by a backslash, and therefore that the two characters '\"' remain as two characters in the subscript (in true double-quoting, '\"' becomes '"'). However, because of the standard shell quoting rules, any double-quotes that appear must occur in balanced pairs unless preceded by a backslash. This makes it more difficult to write a subscript expression that contains an odd number of double-quote characters, but the reason for this difference is so that when a subscript expression appears inside true double-quotes, one can still write '\"' (rather than '\\\"') for '"'. To use an odd number of double quotes as a key in an assignment, use the typeset builtin and an enclosing pair of double quotes; to refer to the value of that key, again use double quotes: typeset -A aa typeset "aa[one\"two\"three\"quotes]"=QQQ print "$aa[one\"two\"three\"quotes]" It is important to note that the quoting rules do not change when a parameter expansion with a subscript is nested inside another subscript expression. That is, it is not necessary to use additional backslashes within the inner subscript expression; they are removed only once, from the innermost subscript outwards. Parameters are also expanded from the innermost subscript first, as each expansion is encountered left to right in the outer expression. A further complication arises from a way in which subscript parsing is _not_ different from double quote parsing. As in true double-quoting, the sequences '\*', and '\@' remain as two characters when they appear in a subscript expression. To use a literal '*' or '@' as an associative array key, the 'e' flag must be used: typeset -A aa aa[(e)*]=star print $aa[(e)*] A last detail must be considered when reverse subscripting is performed. Parameters appearing in the subscript expression are first expanded and then the complete expression is interpreted as a pattern. This has two effects: first, parameters behave as if GLOB_SUBST were on (and it cannot be turned off); second, backslashes are interpreted twice, once when parsing the array subscript and again when parsing the pattern. In a reverse subscript, it's necessary to use _four_ backslashes to cause a single backslash to match literally in the pattern. For complex patterns, it is often easiest to assign the desired pattern to a parameter and then refer to that parameter in the subscript, because then the backslashes, brackets, parentheses, etc., are seen only when the complete expression is converted to a pattern. To match the value of a parameter literally in a reverse subscript, rather than as a pattern, use '${(q)NAME}' (*note Parameter Expansion::) to quote the expanded value. Note that the 'k' and 'K' flags are reverse subscripting for an ordinary array, but are _not_ reverse subscripting for an associative array! (For an associative array, the keys in the array itself are interpreted as patterns by those flags; the subscript is a plain string in that case.) One final note, not directly related to subscripting: the numeric names of positional parameters (*note Positional Parameters::) are parsed specially, so for example '$2foo' is equivalent to '${2}foo'. Therefore, to use subscript syntax to extract a substring from a positional parameter, the expansion must be surrounded by braces; for example, '${2[3,5]}' evaluates to the third through fifth characters of the second positional parameter, but '$2[3,5]' is the entire second parameter concatenated with the filename generation pattern '[3,5]'.  File: zsh.info, Node: Positional Parameters, Next: Local Parameters, Prev: Array Parameters, Up: Parameters 15.3 Positional Parameters ========================== The positional parameters provide access to the command-line arguments of a shell function, shell script, or the shell itself; see *note Invocation::, and also *note Functions::. The parameter N, where N is a number, is the Nth positional parameter. The parameter '$0' is a special case, see *note Parameters Set By The Shell::. The parameters *, @ and argv are arrays containing all the positional parameters; thus '$argv[N]', etc., is equivalent to simply '$N'. Note that the options KSH_ARRAYS or KSH_ZERO_SUBSCRIPT apply to these arrays as well, so with either of those options set, '${argv[0]}' is equivalent to '$1' and so on. Positional parameters may be changed after the shell or function starts by using the set builtin, by assigning to the argv array, or by direct assignment of the form 'N=VALUE' where N is the number of the positional parameter to be changed. This also creates (with empty values) any of the positions from 1 to N that do not already have values. Note that, because the positional parameters form an array, an array assignment of the form 'N=(VALUE ...)' is allowed, and has the effect of shifting all the values at positions greater than N by as many positions as necessary to accommodate the new values.  File: zsh.info, Node: Local Parameters, Next: Parameters Set By The Shell, Prev: Positional Parameters, Up: Parameters 15.4 Local Parameters ===================== Shell function executions delimit scopes for shell parameters. (Parameters are dynamically scoped.) The typeset builtin, and its alternative forms declare, integer, local and readonly (but not export), can be used to declare a parameter as being local to the innermost scope. When a parameter is read or assigned to, the innermost existing parameter of that name is used. (That is, the local parameter hides any less-local parameter.) However, assigning to a non-existent parameter, or declaring a new parameter with export, causes it to be created in the _outer_most scope. Local parameters disappear when their scope ends. unset can be used to delete a parameter while it is still in scope; any outer parameter of the same name remains hidden. Special parameters may also be made local; they retain their special attributes unless either the existing or the newly-created parameter has the -h (hide) attribute. This may have unexpected effects: there is no default value, so if there is no assignment at the point the variable is made local, it will be set to an empty value (or zero in the case of integers). The following: typeset PATH=/new/directory:$PATH is valid for temporarily allowing the shell or programmes called from it to find the programs in /new/directory inside a function. Note that the restriction in older versions of zsh that local parameters were never exported has been removed.  File: zsh.info, Node: Parameters Set By The Shell, Next: Parameters Used By The Shell, Prev: Local Parameters, Up: Parameters 15.5 Parameters Set By The Shell ================================ In the parameter lists that follow, the mark '' indicates that the parameter is special. '' indicates that the parameter does not exist when the shell initializes in sh or ksh emulation mode. The parameters '!', '#', '*', '-', '?', '@', '$', 'ARGC', 'HISTCMD', 'LINENO', 'PPID', 'status', 'TTYIDLE', 'zsh_eval_context', 'ZSH_EVAL_CONTEXT', and 'ZSH_SUBSHELL' are read-only and thus cannot be restored by the user, so they are not output by 'typeset -p'. This also applies to many read-only parameters loaded from modules. The following parameters are automatically set by the shell: ! The process ID of the last command started in the background with &, put into the background with the bg builtin, or spawned with coproc. # The number of positional parameters in decimal. Note that some confusion may occur with the syntax $#PARAM which substitutes the length of PARAM. Use ${#} to resolve ambiguities. In particular, the sequence '$#-...' in an arithmetic expression is interpreted as the length of the parameter -, q.v. ARGC Same as #. $ The process ID of this shell, set when the shell initializes. Processes forked from the shell without executing a new program, such as command substitutions and commands grouped with (...), are subshells that duplicate the current shell, and thus substitute the same value for $$ as their parent shell. - Flags supplied to the shell on invocation or by the set or setopt commands. * An array containing the positional parameters. argv Same as *. Assigning to argv changes the local positional parameters, but argv is _not_ itself a local parameter. Deleting argv with unset in any function deletes it everywhere, although only the innermost positional parameter array is deleted (so * and @ in other scopes are not affected). @ Same as argv[@], even when argv is not set. ? The exit status returned by the last command. 0 The name used to invoke the current shell, or as set by the -c command line option upon invocation. If the FUNCTION_ARGZERO option is set, $0 is set upon entry to a shell function to the name of the function, and upon entry to a sourced script to the name of the script, and reset to its previous value when the function or script returns. status Same as ?. pipestatus An array containing the exit statuses returned by all commands in the last pipeline. _ The last argument of the previous command. Also, this parameter is set in the environment of every command executed to the full pathname of the command. CPUTYPE The machine type (microprocessor class or machine model), as determined at run time. EGID The effective group ID of the shell process. If you have sufficient privileges, you may change the effective group ID of the shell process by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command with a different effective group ID by '(EGID=GID; command)' If this is made local, it is not implicitly set to 0, but may be explicitly set locally. EUID The effective user ID of the shell process. If you have sufficient privileges, you may change the effective user ID of the shell process by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command with a different effective user ID by '(EUID=UID; command)' If this is made local, it is not implicitly set to 0, but may be explicitly set locally. ERRNO The value of errno (see errno(3)) as set by the most recently failed system call. This value is system dependent and is intended for debugging purposes. It is also useful with the zsh/system module which allows the number to be turned into a name or message. To use this parameter, it must first be assigned a value (typically 0 (zero)). It is initially unset for scripting compatibility. FUNCNEST Integer. If greater than or equal to zero, the maximum nesting depth of shell functions. When it is exceeded, an error is raised at the point where a function is called. The default value is determined when the shell is configured, but is typically 500. Increasing the value increases the danger of a runaway function recursion causing the shell to crash. Setting a negative value turns off the check. GID The real group ID of the shell process. If you have sufficient privileges, you may change the group ID of the shell process by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command under a different group ID by '(GID=GID; command)' If this is made local, it is not implicitly set to 0, but may be explicitly set locally. HISTCMD The current history event number in an interactive shell, in other words the event number for the command that caused $HISTCMD to be read. If the current history event modifies the history, HISTCMD changes to the new maximum history event number. HOST The current hostname. LINENO The line number of the current line within the current script, sourced file, or shell function being executed, whichever was started most recently. Note that in the case of shell functions the line number refers to the function as it appeared in the original definition, not necessarily as displayed by the functions builtin. LOGNAME If the corresponding variable is not set in the environment of the shell, it is initialized to the login name corresponding to the current login session. This parameter is exported by default but this can be disabled using the typeset builtin. The value is set to the string returned by the getlogin(3) system call if that is available. MACHTYPE The machine type (microprocessor class or machine model), as determined at compile time. OLDPWD The previous working directory. This is set when the shell initializes and whenever the directory changes. OPTARG The value of the last option argument processed by the getopts command. OPTIND The index of the last option argument processed by the getopts command. OSTYPE The operating system, as determined at compile time. PPID The process ID of the parent of the shell, set when the shell initializes. As with $$, the value does not change in subshells created as a duplicate of the current shell. PWD The present working directory. This is set when the shell initializes and whenever the directory changes. RANDOM A pseudo-random integer from 0 to 32767, newly generated each time this parameter is referenced. The random number generator can be seeded by assigning a numeric value to RANDOM. The values of RANDOM form an intentionally-repeatable pseudo-random sequence; subshells that reference RANDOM will result in identical pseudo-random values unless the value of RANDOM is referenced or seeded in the parent shell in between subshell invocations. SECONDS The number of seconds since shell invocation. If this parameter is assigned a value, then the value returned upon reference will be the value that was assigned plus the number of seconds since the assignment. Unlike other special parameters, the type of the SECONDS parameter can be changed using the typeset command. The type may be changed only to one of the floating point types or back to integer. For example, 'typeset -F SECONDS' causes the value to be reported as a floating point number. The value is available to microsecond accuracy, although the shell may show more or fewer digits depending on the use of typeset. See the documentation for the builtin typeset in *note Shell Builtin Commands:: for more details. SHLVL Incremented by one each time a new shell is started. signals An array containing the names of the signals. Note that with the standard zsh numbering of array indices, where the first element has index 1, the signals are offset by 1 from the signal number used by the operating system. For example, on typical Unix-like systems HUP is signal number 1, but is referred to as $signals[2]. This is because of EXIT at position 1 in the array, which is used internally by zsh but is not known to the operating system. TRY_BLOCK_ERROR In an always block, indicates whether the preceding list of code caused an error. The value is 1 to indicate an error, 0 otherwise. It may be reset, clearing the error condition. See *note Complex Commands:: TRY_BLOCK_INTERRUPT This variable works in a similar way to TRY_BLOCK_ERROR, but represents the status of an interrupt from the signal SIGINT, which typically comes from the keyboard when the user types ^C. If set to 0, any such interrupt will be reset; otherwise, the interrupt is propagated after the always block. Note that it is possible that an interrupt arrives during the execution of the always block; this interrupt is also propagated. TTY The name of the tty associated with the shell, if any. TTYIDLE The idle time of the tty associated with the shell in seconds or -1 if there is no such tty. UID The real user ID of the shell process. If you have sufficient privileges, you may change the user ID of the shell by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command under a different user ID by '(UID=UID; command)' If this is made local, it is not implicitly set to 0, but may be explicitly set locally. USERNAME The username corresponding to the real user ID of the shell process. If you have sufficient privileges, you may change the username (and also the user ID and group ID) of the shell by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command under a different username (and user ID and group ID) by '(USERNAME=USERNAME; command)' VENDOR The vendor, as determined at compile time. zsh_eval_context (ZSH_EVAL_CONTEXT ) An array (colon-separated list) indicating the context of shell code that is being run. Each time a piece of shell code that is stored within the shell is executed a string is temporarily appended to the array to indicate the type of operation that is being performed. Read in order the array gives an indication of the stack of operations being performed with the most immediate context last. Note that the variable does not give information on syntactic context such as pipelines or subshells. Use $ZSH_SUBSHELL to detect subshells. The context is one of the following: cmdarg Code specified by the -c option to the command line that invoked the shell. cmdsubst Command substitution using the `...` or $(...) construct. equalsubst File substitution using the =(...) construct. eval Code executed by the eval builtin. evalautofunc Code executed with the KSH_AUTOLOAD mechanism in order to define an autoloaded function. fc Code from the shell history executed by the -e option to the fc builtin. file Lines of code being read directly from a file, for example by the source builtin. filecode Lines of code being read from a .zwc file instead of directly from the source file. globqual Code executed by the e or + glob qualifier. globsort Code executed to order files by the o glob qualifier. insubst File substitution using the <(...) construct. loadautofunc Code read directly from a file to define an autoloaded function. outsubst File substitution using the >(...) construct. sched Code executed by the sched builtin. shfunc A shell function. stty Code passed to stty by the STTY environment variable. Normally this is passed directly to the system's stty command, so this value is unlikely to be seen in practice. style Code executed as part of a style retrieved by the zstyle builtin from the zsh/zutil module. toplevel The highest execution level of a script or interactive shell. trap Code executed as a trap defined by the trap builtin. Traps defined as functions have the context shfunc. As traps are asynchronous they may have a different hierarchy from other code. zpty Code executed by the zpty builtin from the zsh/zpty module. zregexparse-guard Code executed as a guard by the zregexparse command from the zsh/zutil module. zregexparse-action Code executed as an action by the zregexparse command from the zsh/zutil module. ZSH_ARGZERO If zsh was invoked to run a script, this is the name of the script. Otherwise, it is the name used to invoke the current shell. This is the same as the value of $0 when the POSIX_ARGZERO option is set, but is always available. ZSH_EXECUTION_STRING If the shell was started with the option -c, this contains the argument passed to the option. Otherwise it is not set. ZSH_NAME Expands to the basename of the command used to invoke this instance of zsh. ZSH_PATCHLEVEL The output of 'git describe --tags --long' for the zsh repository used to build the shell. This is most useful in order to keep track of versions of the shell during development between releases; hence most users should not use it and should instead rely on $ZSH_VERSION. zsh_scheduled_events See *note The zsh/sched Module::. ZSH_SCRIPT If zsh was invoked to run a script, this is the name of the script, otherwise it is unset. ZSH_SUBSHELL Readonly integer. Initially zero, incremented each time the shell forks to create a subshell for executing code. Hence '(print $ZSH_SUBSHELL)' and 'print $(print $ZSH_SUBSHELL)' output 1, while '( (print $ZSH_SUBSHELL) )' outputs 2. ZSH_VERSION The version number of the release of zsh.  File: zsh.info, Node: Parameters Used By The Shell, Prev: Parameters Set By The Shell, Up: Parameters 15.6 Parameters Used By The Shell ================================= The following parameters are used by the shell. Again, '' indicates that the parameter is special and '' indicates that the parameter does not exist when the shell initializes in sh or ksh emulation mode. In cases where there are two parameters with an upper- and lowercase form of the same name, such as path and PATH, the lowercase form is an array and the uppercase form is a scalar with the elements of the array joined together by colons. These are similar to tied parameters created via 'typeset -T'. The normal use for the colon-separated form is for exporting to the environment, while the array form is easier to manipulate within the shell. Note that unsetting either of the pair will unset the other; they retain their special properties when recreated, and recreating one of the pair will recreate the other. ARGV0 If exported, its value is used as the argv[0] of external commands. Usually used in constructs like 'ARGV0=emacs nethack'. BAUD The rate in bits per second at which data reaches the terminal. The line editor will use this value in order to compensate for a slow terminal by delaying updates to the display until necessary. If the parameter is unset or the value is zero the compensation mechanism is turned off. The parameter is not set by default. This parameter may be profitably set in some circumstances, e.g. for slow modems dialing into a communications server, or on a slow wide area network. It should be set to the baud rate of the slowest part of the link for best performance. cdpath (CDPATH ) An array (colon-separated list) of directories specifying the search path for the cd command. COLUMNS The number of columns for this terminal session. Used for printing select lists and for the line editor. CORRECT_IGNORE If set, is treated as a pattern during spelling correction. Any potential correction that matches the pattern is ignored. For example, if the value is '_*' then completion functions (which, by convention, have names beginning with '_') will never be offered as spelling corrections. The pattern does not apply to the correction of file names, as applied by the CORRECT_ALL option (so with the example just given files beginning with '_' in the current directory would still be completed). CORRECT_IGNORE_FILE If set, is treated as a pattern during spelling correction of file names. Any file name that matches the pattern is never offered as a correction. For example, if the value is '.*' then dot file names will never be offered as spelling corrections. This is useful with the CORRECT_ALL option. DIRSTACKSIZE The maximum size of the directory stack, by default there is no limit. If the stack gets larger than this, it will be truncated automatically. This is useful with the AUTO_PUSHD option. ENV If the ENV environment variable is set when zsh is invoked as sh or ksh, $ENV is sourced after the profile scripts. The value of ENV is subjected to parameter expansion, command substitution, and arithmetic expansion before being interpreted as a pathname. Note that ENV is _not_ used unless the shell is interactive and zsh is emulating ‘sh’ or ‘ksh’. FCEDIT The default editor for the fc builtin. If FCEDIT is not set, the parameter EDITOR is used; if that is not set either, a builtin default, usually vi, is used. fignore (FIGNORE ) An array (colon separated list) containing the suffixes of files to be ignored during filename completion. However, if completion only generates files with suffixes in this list, then these files are completed anyway. fpath (FPATH ) An array (colon separated list) of directories specifying the search path for function definitions. This path is searched when a function with the -u attribute is referenced. If an executable file is found, then it is read and executed in the current environment. histchars Three characters used by the shell's history and lexical analysis mechanism. The first character signals the start of a history expansion (default '!'). The second character signals the start of a quick history substitution (default '^'). The third character is the comment character (default '#'). The characters must be in the ASCII character set; any attempt to set histchars to characters with a locale-dependent meaning will be rejected with an error message. HISTCHARS Same as histchars. (Deprecated.) HISTFILE The file to save the history in when an interactive shell exits. If unset, the history is not saved. HISTORY_IGNORE If set, is treated as a pattern at the time history files are written. Any potential history entry that matches the pattern is skipped. For example, if the value is 'fc *' then commands that invoke the interactive history editor are never written to the history file. Note that HISTORY_IGNORE defines a single pattern: to specify alternatives use the '(FIRST|SECOND|...)' syntax. Compare the HIST_NO_STORE option or the zshaddhistory hook, either of which would prevent such commands from being added to the interactive history at all. If you wish to use HISTORY_IGNORE to stop history being added in the first place, you can define the following hook: zshaddhistory() { emulate -L zsh ## uncomment if HISTORY_IGNORE ## should use EXTENDED_GLOB syntax # setopt extendedglob [[ $1 != ${~HISTORY_IGNORE} ]] } HISTSIZE The maximum number of events stored in the internal history list. If you use the HIST_EXPIRE_DUPS_FIRST option, setting this value larger than the SAVEHIST size will give you the difference as a cushion for saving duplicated history events. If this is made local, it is not implicitly set to 0, but may be explicitly set locally. HOME The default argument for the cd command. This is not set automatically by the shell in sh, ksh or csh emulation, but it is typically present in the environment anyway, and if it becomes set it has its usual special behaviour. IFS Internal field separators (by default space, tab, newline and NUL), that are used to separate words which result from command or parameter expansion and words read by the read builtin. Any characters from the set space, tab and newline that appear in the IFS are called _IFS white space_. One or more IFS white space characters or one non-IFS white space character together with any adjacent IFS white space character delimit a field. If an IFS white space character appears twice consecutively in the IFS, this character is treated as if it were not an IFS white space character. If the parameter is unset, the default is used. Note this has a different effect from setting the parameter to an empty string. KEYBOARD_HACK This variable defines a character to be removed from the end of the command line before interpreting it (interactive shells only). It is intended to fix the problem with keys placed annoyingly close to return and replaces the SUNKEYBOARDHACK option which did this for backquotes only. Should the chosen character be one of singlequote, doublequote or backquote, there must also be an odd number of them on the command line for the last one to be removed. For backward compatibility, if the SUNKEYBOARDHACK option is explicitly set, the value of KEYBOARD_HACK reverts to backquote. If the option is explicitly unset, this variable is set to empty. KEYTIMEOUT The time the shell waits, in hundredths of seconds, for another key to be pressed when reading bound multi-character sequences. LANG This variable determines the locale category for any category not specifically selected via a variable starting with 'LC_'. LC_ALL This variable overrides the value of the 'LANG' variable and the value of any of the other variables starting with 'LC_'. LC_COLLATE This variable determines the locale category for character collation information within ranges in glob brackets and for sorting. LC_CTYPE This variable determines the locale category for character handling functions. If the MULTIBYTE option is in effect this variable or LANG should contain a value that reflects the character set in use, even if it is a single-byte character set, unless only the 7-bit subset (ASCII) is used. For example, if the character set is ISO-8859-1, a suitable value might be en_US.iso88591 (certain Linux distributions) or en_US.ISO8859-1 (MacOS). LC_MESSAGES This variable determines the language in which messages should be written. Note that zsh does not use message catalogs. LC_NUMERIC This variable affects the decimal point character and thousands separator character for the formatted input/output functions and string conversion functions. Note that zsh ignores this setting when parsing floating point mathematical expressions. LC_TIME This variable determines the locale category for date and time formatting in prompt escape sequences. LINES The number of lines for this terminal session. Used for printing select lists and for the line editor. LISTMAX In the line editor, the number of matches to list without asking first. If the value is negative, the list will be shown if it spans at most as many lines as given by the absolute value. If set to zero, the shell asks only if the top of the listing would scroll off the screen. MAIL If this parameter is set and mailpath is not set, the shell looks for mail in the specified file. MAILCHECK The interval in seconds between checks for new mail. mailpath (MAILPATH ) An array (colon-separated list) of filenames to check for new mail. Each filename can be followed by a '?' and a message that will be printed. The message will undergo parameter expansion, command substitution and arithmetic expansion with the variable $_ defined as the name of the file that has changed. The default message is 'You have new mail'. If an element is a directory instead of a file the shell will recursively check every file in every subdirectory of the element. manpath (MANPATH ) An array (colon-separated list) whose value is not used by the shell. The manpath array can be useful, however, since setting it also sets MANPATH, and vice versa. match mbegin mend Arrays set by the shell when the b globbing flag is used in pattern matches. See the subsection _Globbing flags_ in *note Filename Generation::. MATCH MBEGIN MEND Set by the shell when the m globbing flag is used in pattern matches. See the subsection _Globbing flags_ in *note Filename Generation::. module_path (MODULE_PATH ) An array (colon-separated list) of directories that zmodload searches for dynamically loadable modules. This is initialized to a standard pathname, usually '/usr/local/lib/zsh/$ZSH_VERSION'. (The '/usr/local/lib' part varies from installation to installation.) For security reasons, any value set in the environment when the shell is started will be ignored. These parameters only exist if the installation supports dynamic module loading. NULLCMD The command name to assume if a redirection is specified with no command. Defaults to cat. For ‘sh’/‘ksh’ behavior, change this to :. For ‘csh’-like behavior, unset this parameter; the shell will print an error message if null commands are entered. path (PATH ) An array (colon-separated list) of directories to search for commands. When this parameter is set, each directory is scanned and all files found are put in a hash table. POSTEDIT This string is output whenever the line editor exits. It usually contains termcap strings to reset the terminal. PROMPT PROMPT2 PROMPT3 PROMPT4 Same as PS1, PS2, PS3 and PS4, respectively. prompt Same as PS1. PROMPT_EOL_MARK When the PROMPT_CR and PROMPT_SP options are set, the PROMPT_EOL_MARK parameter can be used to customize how the end of partial lines are shown. This parameter undergoes prompt expansion, with the PROMPT_PERCENT option set. If not set, the default behavior is equivalent to the value '%B%S%#%s%b'. PS1 The primary prompt string, printed before a command is read. It undergoes a special form of expansion before being displayed; see *note Prompt Expansion::. The default is '%m%# '. PS2 The secondary prompt, printed when the shell needs more information to complete a command. It is expanded in the same way as PS1. The default is '%_> ', which displays any shell constructs or quotation marks which are currently being processed. PS3 Selection prompt used within a select loop. It is expanded in the same way as PS1. The default is '?# '. PS4 The execution trace prompt. Default is '+%N:%i> ', which displays the name of the current shell structure and the line number within it. In sh or ksh emulation, the default is '+ '. psvar (PSVAR ) An array (colon-separated list) whose elements can be used in PROMPT strings. Setting psvar also sets PSVAR, and vice versa. READNULLCMD The command name to assume if a single input redirection is specified with no command. Defaults to more. REPORTMEMORY If nonnegative, commands whose maximum resident set size (roughly speaking, main memory usage) in kilobytes is greater than this value have timing statistics reported. The format used to output statistics is the value of the TIMEFMT parameter, which is the same as for the REPORTTIME variable and the time builtin; note that by default this does not output memory usage. Appending " max RSS %M" to the value of TIMEFMT causes it to output the value that triggered the report. If REPORTTIME is also in use, at most a single report is printed for both triggers. This feature requires the getrusage() system call, commonly supported by modern Unix-like systems. REPORTTIME If nonnegative, commands whose combined user and system execution times (measured in seconds) are greater than this value have timing statistics printed for them. Output is suppressed for commands executed within the line editor, including completion; commands explicitly marked with the time keyword still cause the summary to be printed in this case. REPLY This parameter is reserved by convention to pass string values between shell scripts and shell builtins in situations where a function call or redirection are impossible or undesirable. The read builtin and the select complex command may set REPLY, and filename generation both sets and examines its value when evaluating certain expressions. Some modules also employ REPLY for similar purposes. reply As REPLY, but for array values rather than strings. RPROMPT RPS1 This prompt is displayed on the right-hand side of the screen when the primary prompt is being displayed on the left. This does not work if the SINGLE_LINE_ZLE option is set. It is expanded in the same way as PS1. RPROMPT2 RPS2 This prompt is displayed on the right-hand side of the screen when the secondary prompt is being displayed on the left. This does not work if the SINGLE_LINE_ZLE option is set. It is expanded in the same way as PS2. SAVEHIST The maximum number of history events to save in the history file. If this is made local, it is not implicitly set to 0, but may be explicitly set locally. SPROMPT The prompt used for spelling correction. The sequence '%R' expands to the string which presumably needs spelling correction, and '%r' expands to the proposed correction. All other prompt escapes are also allowed. The actions available at the prompt are [nyae]: n ('no') (default) Discard the correction and run the command. y ('yes') Make the correction and run the command. a ('abort') Discard the entire command line without running it. e ('edit') Resume editing the command line. STTY If this parameter is set in a command's environment, the shell runs the stty command with the value of this parameter as arguments in order to set up the terminal before executing the command. The modes apply only to the command, and are reset when it finishes or is suspended. If the command is suspended and continued later with the fg or wait builtins it will see the modes specified by STTY, as if it were not suspended. This (intentionally) does not apply if the command is continued via 'kill -CONT'. STTY is ignored if the command is run in the background, or if it is in the environment of the shell but not explicitly assigned to in the input line. This avoids running stty at every external command by accidentally exporting it. Also note that STTY should not be used for window size specifications; these will not be local to the command. If the parameter is set and empty, all of the above applies except that stty is not run. This can be useful as a way to freeze the tty around a single command, blocking its changes to tty settings, similar to the ttyctl builtin. TERM The type of terminal in use. This is used when looking up termcap sequences. An assignment to TERM causes zsh to re-initialize the terminal, even if the value does not change (e.g., 'TERM=$TERM'). It is necessary to make such an assignment upon any change to the terminal definition database or terminal type in order for the new settings to take effect. TERMINFO A reference to your terminfo database, used by the 'terminfo' library when the system has it; see terminfo(5). If set, this causes the shell to reinitialise the terminal, making the workaround 'TERM=$TERM' unnecessary. TERMINFO_DIRS A colon-seprarated list of terminfo databases, used by the 'terminfo' library when the system has it; see terminfo(5). This variable is only used by certain terminal libraries, in particular ncurses; see terminfo(5) to check support on your system. If set, this causes the shell to reinitialise the terminal, making the workaround 'TERM=$TERM' unnecessary. Note that unlike other colon-separated arrays this is not tied to a zsh array. TIMEFMT The format of process time reports with the time keyword. The default is '%J %U user %S system %P cpu %*E total'. Recognizes the following escape sequences, although not all may be available on all systems, and some that are available may not be useful: %% A '%'. %U CPU seconds spent in user mode. %S CPU seconds spent in kernel mode. %E Elapsed time in seconds. %P The CPU percentage, computed as 100*(%U+%S)/%E. %W Number of times the process was swapped. %X The average amount in (shared) text space used in kilobytes. %D The average amount in (unshared) data/stack space used in kilobytes. %K The total space used (%X+%D) in kilobytes. %M The maximum memory the process had in use at any time in kilobytes. %F The number of major page faults (page needed to be brought from disk). %R The number of minor page faults. %I The number of input operations. %O The number of output operations. %r The number of socket messages received. %s The number of socket messages sent. %k The number of signals received. %w Number of voluntary context switches (waits). %c Number of involuntary context switches. %J The name of this job. A star may be inserted between the percent sign and flags printing time (e.g., '%*E'); this causes the time to be printed in 'HH:MM:SS.TTT' format (hours and minutes are only printed if they are not zero). Alternatively, 'm' or 'u' may be used (e.g., '%mE') to produce time output in milliseconds or microseconds, respectively. TMOUT If this parameter is nonzero, the shell will receive an ALRM signal if a command is not entered within the specified number of seconds after issuing a prompt. If there is a trap on SIGALRM, it will be executed and a new alarm is scheduled using the value of the TMOUT parameter after executing the trap. If no trap is set, and the idle time of the terminal is not less than the value of the TMOUT parameter, zsh terminates. Otherwise a new alarm is scheduled to TMOUT seconds after the last keypress. TMPPREFIX A pathname prefix which the shell will use for all temporary files. Note that this should include an initial part for the file name as well as any directory names. The default is '/tmp/zsh'. TMPSUFFIX A filename suffix which the shell will use for temporary files created by process substitutions (e.g., '=(LIST)'). Note that the value should include a leading dot '.' if intended to be interpreted as a file extension. The default is not to append any suffix, thus this parameter should be assigned only when needed and then unset again. WORDCHARS A list of non-alphanumeric characters considered part of a word by the line editor. ZBEEP If set, this gives a string of characters, which can use all the same codes as the bindkey command as described in *note The zsh/zle Module::, that will be output to the terminal instead of beeping. This may have a visible instead of an audible effect; for example, the string '\e[?5h\e[?5l' on a vt100 or xterm will have the effect of flashing reverse video on and off (if you usually use reverse video, you should use the string '\e[?5l\e[?5h' instead). This takes precedence over the NOBEEP option. ZDOTDIR The directory to search for shell startup files (.zshrc, etc), if not $HOME. zle_bracketed_paste Many terminal emulators have a feature that allows applications to identify when text is pasted into the terminal rather than being typed normally. For ZLE, this means that special characters such as tabs and newlines can be inserted instead of invoking editor commands. Furthermore, pasted text forms a single undo event and if the region is active, pasted text will replace the region. This two-element array contains the terminal escape sequences for enabling and disabling the feature. These escape sequences are used to enable bracketed paste when ZLE is active and disable it at other times. Unsetting the parameter has the effect of ensuring that bracketed paste remains disabled. zle_highlight An array describing contexts in which ZLE should highlight the input text. See *note Character Highlighting::. ZLE_LINE_ABORTED This parameter is set by the line editor when an error occurs. It contains the line that was being edited at the point of the error. 'print -zr -- $ZLE_LINE_ABORTED' can be used to recover the line. Only the most recent line of this kind is remembered. ZLE_REMOVE_SUFFIX_CHARS ZLE_SPACE_SUFFIX_CHARS These parameters are used by the line editor. In certain circumstances suffixes (typically space or slash) added by the completion system will be removed automatically, either because the next editing command was not an insertable character, or because the character was marked as requiring the suffix to be removed. These variables can contain the sets of characters that will cause the suffix to be removed. If ZLE_REMOVE_SUFFIX_CHARS is set, those characters will cause the suffix to be removed; if ZLE_SPACE_SUFFIX_CHARS is set, those characters will cause the suffix to be removed and replaced by a space. If ZLE_REMOVE_SUFFIX_CHARS is not set, the default behaviour is equivalent to: ZLE_REMOVE_SUFFIX_CHARS=$' \t\n;&|' If ZLE_REMOVE_SUFFIX_CHARS is set but is empty, no characters have this behaviour. ZLE_SPACE_SUFFIX_CHARS takes precedence, so that the following: ZLE_SPACE_SUFFIX_CHARS=$'&|' causes the characters '&' and '|' to remove the suffix but to replace it with a space. To illustrate the difference, suppose that the option AUTO_REMOVE_SLASH is in effect and the directory DIR has just been completed, with an appended /, following which the user types '&'. The default result is 'DIR&'. With ZLE_REMOVE_SUFFIX_CHARS set but without including '&' the result is 'DIR/&'. With ZLE_SPACE_SUFFIX_CHARS set to include '&' the result is 'DIR &'. Note that certain completions may provide their own suffix removal or replacement behaviour which overrides the values described here. See the completion system documentation in *note Completion System::. ZLE_RPROMPT_INDENT If set, used to give the indentation between the right hand side of the right prompt in the line editor as given by RPS1 or RPROMPT and the right hand side of the screen. If not set, the value 1 is used. Typically this will be used to set the value to 0 so that the prompt appears flush with the right hand side of the screen. This is not the default as many terminals do not handle this correctly, in particular when the prompt appears at the extreme bottom right of the screen. Recent virtual terminals are more likely to handle this case correctly. Some experimentation is necessary.