Invocation

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 zshoptions.

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 zshbuiltins. 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.

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, 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, https://www.zsh.org/FAQ/.