zsh: 4. Invocation

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# 4. Invocation

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## 4.1 Invocation Options

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.

`-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.

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 Options.

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.

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## 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 ``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`, `watch`.

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`.

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## 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 `PATH`, `path`, `MODULE_PATH`, `module_path`, `SHELL`, `HISTFILE`, `HISTSIZE`, `GID`, `EGID`, `UID`, `EUID`, `USERNAME`, `LD_LIBRARY_PATH`, `LD_AOUT_LIBRARY_PATH`, `LD_PRELOAD` and `LD_AOUT_PRELOAD` 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.

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This document was generated by Peter Stephenson on April, 2 2008 using texi2html 1.78.