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<H1> 3. Invocation </H1>
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<H2> 3.1 Invocation Options </H2>
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The following flags are interpreted by the shell when invoked to determine
where the shell will read commands from:
<P>
</P>
<DL COMPACT>
<DT><TT>-c</TT>
<DD>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 <TT>$0</TT>, rather than being used as a positional
parameter.
<P>
</P>
<DT><TT>-i</TT>
<DD>Force shell to be interactive.
<P>
</P>
<DT><TT>-s</TT>
<DD>Force shell to read commands from the standard input.
If the <TT>-s</TT> flag is not present and an argument is given,
the first argument is taken to be the pathname of a script to
execute.
<P>
</DL>
<P>
After the first one or two arguments have been appropriated as described above,
the remaining arguments are assigned to the positional parameters.
</P>
<P>
For further options, which are common to invocation and the <TT>set</TT>
builtin, see
<A HREF="zsh_15.html#SEC74">15. Options</A>.
</P>
<P>
Options may be specified by name using the <TT>-o</TT> option. <TT>-o</TT> acts like
a single-letter option, but takes a following string as the option name.
For example,
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>zsh -x -o shwordsplit scr
</pre></td></tr></table><P>
runs the script <TT>scr</TT>, setting the <TT>XTRACE</TT> option by the corresponding
letter `<TT>-x</TT>' and the <TT>SH_WORD_SPLIT</TT> option by name.
Options may be turned <EM>off</EM> by name by using <TT>+o</TT> instead of <TT>-o</TT>.
<TT>-o</TT> can be stacked up with preceding single-letter options, so for example
`<TT>-xo shwordsplit</TT>' or `<TT>-xoshwordsplit</TT>' is equivalent to
`<TT>-x -o shwordsplit</TT>'.
</P>
<P>
Options may also be specified by name in GNU long option style,
`<TT>--</TT><VAR>option-name</VAR>'. When this is done, `<TT>-</TT>' characters in the
option name are permitted: they are translated into `<TT>_</TT>', and thus ignored.
So, for example, `<TT>zsh --sh-word-split</TT>' invokes zsh with the
<TT>SH_WORD_SPLIT</TT> option turned on. Like other option syntaxes, options can
be turned off by replacing the initial `<TT>-</TT>' with a `<TT>+</TT>'; thus
`<TT>+-sh-word-split</TT>' is equivalent to `<TT>--no-sh-word-split</TT>'.
Unlike other option syntaxes, GNU-style long options cannot be stacked with
any other options, so for example `<TT>-x-shwordsplit</TT>' is an error,
rather than being treated like `<TT>-x --shwordsplit</TT>'.
</P>
<P>
The special GNU-style option `<TT>--version</TT>' is handled; it sends to standard
output the shell's version information, then exits successfully.
`<TT>--help</TT>' is also handled; it sends to standard output a list of options
that can be used when invoking the shell, then exits successfully.
</P>
<P>
Option processing may be finished, allowing following arguments that start with
`<TT>-</TT>' or `<TT>+</TT>' to be treated as normal arguments, in two ways.
Firstly, a lone `<TT>-</TT>' (or `<TT>+</TT>') as an argument by itself ends option
processing. Secondly, a special option `<TT>--</TT>' (or `<TT>+-</TT>'), which may
be specified on its own (which is the standard POSIX usage) or may be stacked
with preceding options (so `<TT>-x-</TT>' is equivalent to `<TT>-x --</TT>'). Options
are not permitted to be stacked after `<TT>--</TT>' (so `<TT>-x-f</TT>' is an error),
but note the GNU-style option form discussed above, where `<TT>--shwordsplit</TT>'
is permitted and does not end option processing.
</P>
<P>
Except when the <CITE>sh</CITE>/<CITE>ksh</CITE> emulation single-letter options are in effect,
the option `<TT>-b</TT>' (or `<TT>+b</TT>') ends option processing.
`<TT>-b</TT>' is like `<TT>--</TT>', except that further single-letter options can be
stacked after the `<TT>-b</TT>' and will take effect as normal.
</P>
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="zsh_3.html#SEC13">3.2 Compatibility</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="zsh_3.html#SEC14">3.3 Restricted Shell</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
</TABLE>
<P>
<A NAME="Compatibility"></A>
</P>
<P>
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<H2> 3.2 Compatibility </H2>
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Zsh tries to emulate <CITE>sh</CITE> or <CITE>ksh</CITE> when it is invoked as
<TT>sh</TT> or <TT>ksh</TT> respectively; more precisely, it looks at the first
letter of the name by which it was invoked, excluding any initial `<TT>r</TT>'
(assumed to stand for `restricted'), and if that is `<TT>s</TT>' or `<TT>k</TT>' it
will emulate <CITE>sh</CITE> or <CITE>ksh</CITE>. Furthermore, if invoked as <TT>su</TT> (which
happens on certain systems when the shell is executed by the <TT>su</TT>
command), the shell will try to find an alternative name from the <TT>SHELL</TT>
environment variable and perform emulation based on that.
<P>
In <CITE>sh</CITE> and <CITE>ksh</CITE> compatibility modes the following
parameters are not special and not initialized by the shell:
<TT>ARGC</TT>,
<TT>argv</TT>,
<TT>cdpath</TT>,
<TT>fignore</TT>,
<TT>fpath</TT>,
<TT>HISTCHARS</TT>,
<TT>mailpath</TT>,
<TT>MANPATH</TT>,
<TT>manpath</TT>,
<TT>path</TT>,
<TT>prompt</TT>,
<TT>PROMPT</TT>,
<TT>PROMPT2</TT>,
<TT>PROMPT3</TT>,
<TT>PROMPT4</TT>,
<TT>psvar</TT>,
<TT>status</TT>,
<TT>watch</TT>.
</P>
<P>
The usual zsh startup/shutdown scripts are not executed. Login shells
source <TT>/etc/profile</TT> followed by <TT>$HOME/.profile</TT>. If the
<TT>ENV</TT> environment variable is set on invocation, <TT>$ENV</TT> is sourced
after the profile scripts. The value of <TT>ENV</TT> is subjected to
parameter expansion, command substitution, and arithmetic expansion
before being interpreted as a pathname. Note that the <TT>PRIVILEGED</TT>
option also affects the execution of startup files.
</P>
<P>
The following options are set if the shell is invoked as <TT>sh</TT> or
<TT>ksh</TT>:
<TT>NO_BAD_PATTERN</TT>,
<TT>NO_BANG_HIST</TT>,
<TT>NO_BG_NICE</TT>,
<TT>NO_EQUALS</TT>,
<TT>NO_FUNCTION_ARGZERO</TT>,
<TT>GLOB_SUBST</TT>,
<TT>NO_GLOBAL_EXPORT</TT>,
<TT>NO_HUP</TT>,
<TT>INTERACTIVE_COMMENTS</TT>,
<TT>KSH_ARRAYS</TT>,
<TT>NO_MULTIOS</TT>,
<TT>NO_NOMATCH</TT>,
<TT>NO_NOTIFY</TT>,
<TT>POSIX_BUILTINS</TT>,
<TT>NO_PROMPT_PERCENT</TT>,
<TT>RM_STAR_SILENT</TT>,
<TT>SH_FILE_EXPANSION</TT>,
<TT>SH_GLOB</TT>,
<TT>SH_OPTION_LETTERS</TT>,
<TT>SH_WORD_SPLIT</TT>.
Additionally the <TT>BSD_ECHO</TT> and <TT>IGNORE_BRACES</TT>
options are set if zsh is invoked as <TT>sh</TT>.
Also, the
<TT>KSH_OPTION_PRINT</TT>,
<TT>LOCAL_OPTIONS</TT>,
<TT>PROMPT_BANG</TT>,
<TT>PROMPT_SUBST</TT>
and
<TT>SINGLE_LINE_ZLE</TT>
options are set if zsh is invoked as <TT>ksh</TT>.
<A NAME="Restricted Shell"></A>
</P>
<P>
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<H2> 3.3 Restricted Shell </H2>
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When the basename of the command used to invoke zsh starts with the letter
`<TT>r</TT>' or the `<TT>-r</TT>' command line option is supplied at invocation, the
shell becomes restricted. Emulation mode is determined after stripping the
letter `<TT>r</TT>' from the invocation name. The following are disabled in
restricted mode:
<P>
<UL>
<LI>
changing directories with the <TT>cd</TT> builtin
<LI>
changing or unsetting the <TT>PATH</TT>, <TT>path</TT>, <TT>MODULE_PATH</TT>,
<TT>module_path</TT>, <TT>SHELL</TT>, <TT>HISTFILE</TT>, <TT>HISTSIZE</TT>, <TT>GID</TT>, <TT>EGID</TT>,
<TT>UID</TT>, <TT>EUID</TT>, <TT>USERNAME</TT>, <TT>LD_LIBRARY_PATH</TT>,
<TT>LD_AOUT_LIBRARY_PATH</TT>, <TT>LD_PRELOAD</TT> and <TT>LD_AOUT_PRELOAD</TT>
parameters
<LI>
specifying command names containing <TT>/</TT>
<LI>
specifying command pathnames using <TT>hash</TT>
<LI>
redirecting output to files
<LI>
using the <TT>exec</TT> builtin command to replace the shell with another
command
<LI>
using <TT>jobs -Z</TT> to overwrite the shell process' argument and
environment space
<LI>
using the <TT>ARGV0</TT> parameter to override <TT>argv[0]</TT> for external
commands
<LI>
turning off restricted mode with <TT>set +r</TT> or <TT>unsetopt
RESTRICTED</TT>
</UL>
<P>
These restrictions are enforced after processing the startup files. The
startup files should set up <TT>PATH</TT> 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.
</P>
<P>
Restricted mode can also be activated any time by setting the
<TT>RESTRICTED</TT> option. This immediately enables all the restrictions
described above even if the shell still has not processed all startup
files.
<A NAME="Files"></A>
</P>
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