ZSH(1) General Commands Manual ZSH(1)
NAME
zsh - the Z shell
OVERVIEW
Because zsh contains many features, the zsh manual has been split into
a number of sections:
zsh Zsh overview (this section)
zshroadmap Informal introduction to the manual
zshmisc Anything not fitting into the other sections
zshexpn Zsh command and parameter expansion
zshparam Zsh parameters
zshoptions Zsh options
zshbuiltins Zsh built-in functions
zshzle Zsh command line editing
zshcompwid Zsh completion widgets
zshcompsys Zsh completion system
zshcompctl Zsh completion control
zshmodules Zsh loadable modules
zshcalsys Zsh built-in calendar functions
zshtcpsys Zsh built-in TCP functions
zshzftpsys Zsh built-in FTP client
zshcontrib Additional zsh functions and utilities
zshall Meta-man page containing all of the above
DESCRIPTION
Zsh is a UNIX command interpreter (shell) usable as an interactive lo-
gin 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 de-
fault operating mode: see the section `Compatibility' below.
Zsh has command line editing, builtin spelling correction, programmable
command completion, shell functions (with autoloading), a history mech-
anism, and a host of other features.
AUTHOR
Zsh was originally written by Paul Falstad. Zsh is now maintained by
the members of the zsh-workers mailing list <zsh-workers@zsh.org>. The
development is currently coordinated by Peter Stephenson <pws@zsh.org>.
The coordinator can be contacted at <coordinator@zsh.org>, but matters
relating to the code should generally go to the mailing list.
AVAILABILITY
Zsh is available from the following HTTP and anonymous FTP site.
ftp://ftp.zsh.org/pub/
https://www.zsh.org/pub/
The up-to-date source code is available via Git from Sourceforge. See
https://sourceforge.net/projects/zsh/ for details. A summary of in-
structions for the archive can be found at https://zsh.sourceforge.io/.
MAILING LISTS
Zsh has several mailing lists:
<zsh-announce@zsh.org>
Announcements about releases, major changes in the shell and the
monthly posting of the Zsh FAQ. (moderated)
<zsh-users@zsh.org>
User discussions.
<zsh-workers@zsh.org>
Hacking, development, bug reports and patches.
<zsh-security@zsh.org>
Private mailing list (the general public cannot subscribe to it)
for discussing bug reports with security implications, i.e., po-
tential 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.
<zsh-announce-subscribe@zsh.org>
<zsh-users-subscribe@zsh.org>
<zsh-workers-subscribe@zsh.org>
<zsh-announce-unsubscribe@zsh.org>
<zsh-users-unsubscribe@zsh.org>
<zsh-workers-unsubscribe@zsh.org>
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-work-
ers.
If you have problems subscribing/unsubscribing to any of the mailing
lists, send mail to <listmaster@zsh.org>.
The mailing lists are archived; the archives can be accessed via the
administrative addresses listed above. There is also a hypertext ar-
chive available at https://www.zsh.org/mla/.
THE ZSH FAQ
Zsh has a list of Frequently Asked Questions (FAQ), maintained by Peter
Stephenson <pws@zsh.org>. 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
https://www.zsh.org/FAQ/. The contact address for FAQ-related matters
is <faqmaster@zsh.org>.
THE ZSH WEB PAGE
Zsh has a web page which is located at https://www.zsh.org/. The con-
tact address for web-related matters is <webmaster@zsh.org>.
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 https://zsh.sourceforge.io/Guide/. At the time of writing,
chapters dealing with startup files and their contents and the new com-
pletion system were essentially complete.
INVOCATION
The following flags are interpreted by the shell when invoked to deter-
mine 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 fur-
ther 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 nei-
ther 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 de-
scribed above, the remaining arguments are assigned to the positional
parameters.
For further options, which are common to invocation and the set
builtin, see zshoptions(1).
The long option `--emulate' followed (in a separate word) by an emula-
tion mode may be passed to the shell. The emulation modes are those
described for the emulate builtin, see zshbuiltins(1). The `--emulate'
option must precede any other options (which might otherwise be over-
ridden), 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, `--op-
tion-name'. When this is done, `-' characters in the option name are
permitted: they are translated into `_', and thus ignored. So, for ex-
ample, `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 equiva-
lent 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 stan-
dard 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 pro-
cessing. Secondly, a special option `--' (or `+-'), which may be spec-
ified 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.
COMPATIBILITY
Zsh tries to emulate sh or ksh when it is invoked as sh or ksh respec-
tively; 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 per-
form emulation based on that.
In sh and ksh compatibility modes the following parameters are not spe-
cial 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_FUNC-
TION_ARGZERO, GLOB_SUBST, NO_GLOBAL_EXPORT, NO_HUP, INTERACTIVE_COM-
MENTS, KSH_ARRAYS, NO_MULTIOS, NO_NOMATCH, NO_NOTIFY, POSIX_BUILTINS,
NO_PROMPT_PERCENT, RM_STAR_SILENT, SH_FILE_EXPANSION, SH_GLOB, SH_OP-
TION_LETTERS, SH_WORD_SPLIT. Additionally the BSD_ECHO and IG-
NORE_BRACES options are set if zsh is invoked as sh. Also, the KSH_OP-
TION_PRINT, LOCAL_OPTIONS, PROMPT_BANG, PROMPT_SUBST and SIN-
GLE_LINE_ZLE options are set if zsh is invoked as ksh.
Please note that, whilst reasonable efforts are taken to address incom-
patibilities when they arise, zsh does not guarantee complete emulation
of other shells, nor POSIX compliance. For more information on the dif-
ferences between zsh and other shells, please refer to chapter 2 of the
shell FAQ, https://www.zsh.org/FAQ/.
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 envi-
ronment space
• using the ARGV0 parameter to override argv[0] for external com-
mands
• 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 com-
mands 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 RE-
STRICTED option. This immediately enables all the restrictions de-
scribed 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 con-
fine 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 com-
mand 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 vari-
ables. Except for the few listed above, zsh does not restrict the set-
ting 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 care-
fully 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', al-
low bypassing most of the restrictions.
STARTUP/SHUTDOWN FILES
Commands are first read from /etc/zsh/zshenv; this cannot be overrid-
den. Subsequent behaviour is modified by the RCS and GLOBAL_RCS op-
tions; the former affects all startup files, while the second only af-
fects 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/zsh/zprofile and then $ZDOT-
DIR/.zprofile. Then, if the shell is interactive, commands are read
from /etc/zsh/zshrc and then $ZDOTDIR/.zshrc. Finally, if the shell is
a login shell, /etc/zsh/zlogin and $ZDOTDIR/.zlogin are read.
When a login shell exits, the files $ZDOTDIR/.zlogout and then
/etc/zsh/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/zsh/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.
Any of these files may be pre-compiled with the zcompile builtin com-
mand (see zshbuiltins(1)). If a compiled file exists (named for the
original file plus the .zwc extension) and it is newer than the origi-
nal file, the compiled file will be used instead.
FILES
$ZDOTDIR/.zshenv
$ZDOTDIR/.zprofile
$ZDOTDIR/.zshrc
$ZDOTDIR/.zlogin
$ZDOTDIR/.zlogout
${TMPPREFIX}* (default is /tmp/zsh*)
/etc/zsh/zshenv
/etc/zsh/zprofile
/etc/zsh/zshrc
/etc/zsh/zlogin
/etc/zsh/zlogout (installation-specific - /etc is the default)
SEE ALSO
sh(1), csh(1), tcsh(1), rc(1), bash(1), ksh(1), zshall(1), zsh-
builtins(1), zshcalsys(1), zshcompwid(1), zshcompsys(1), zshcompctl(1),
zshcontrib(1), zshexpn(1), zshmisc(1), zshmodules(1), zshoptions(1),
zshparam(1), zshroadmap(1), zshtcpsys(1), zshzftpsys(1), zshzle(1)
IEEE Standard for information Technology - Portable Operating System
Interface (POSIX) - Part 2: Shell and Utilities, IEEE Inc, 1993, ISBN
1-55937-255-9.
zsh 5.9 May 14, 2022 ZSH(1)
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