129 lines
4.5 KiB
HTML
129 lines
4.5 KiB
HTML
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
|
||
|
|
<html>
|
||
|
|
<head>
|
||
|
|
<meta name="generator" content="HTML Tidy, see www.w3.org">
|
||
|
|
<meta http-equiv="Content-Type" content=
|
||
|
|
"text/html; charset=utf-8">
|
||
|
|
<title>Simple commands</title>
|
||
|
|
<LINK rel="stylesheet" type="text/css" href="../rzahg/ic.css">
|
||
|
|
</HEAD>
|
||
|
|
<body bgcolor="#FFFFFF">
|
||
|
|
<!-- Java sync-link -->
|
||
|
|
<SCRIPT LANGUAGE="Javascript" SRC="../rzahg/synch.js" TYPE="text/javascript"></SCRIPT>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
<h2>Simple commands</h2>
|
||
|
|
|
||
|
|
<p>A simple command is a sequence of optional variable assignments
|
||
|
|
and redirections followed by a command name. When a simple command
|
||
|
|
is recognized by <strong>qsh</strong>, it performs the following
|
||
|
|
actions:</p>
|
||
|
|
|
||
|
|
<ol>
|
||
|
|
<li>Leading words of the form name=value are stripped off and
|
||
|
|
assigned to the environment of the simple command. Redirection
|
||
|
|
operators and their arguments are saved for processing in step
|
||
|
|
3.</li>
|
||
|
|
|
||
|
|
<li>The remaining words are expanded as described in <a href=
|
||
|
|
"wordexp.htm">Word expansions</a>, and the first remaining word is
|
||
|
|
considered the command name. Any additional words are considered
|
||
|
|
the arguments of the command. If no command name is found, then the
|
||
|
|
name=value variable assignments recognized in step 1 affect the
|
||
|
|
current shell.</li>
|
||
|
|
|
||
|
|
<li>Redirections are performed as described in <a href=
|
||
|
|
"redirect.htm">Redirection</a>.</li>
|
||
|
|
</ol>
|
||
|
|
|
||
|
|
<strong>Path search</strong>
|
||
|
|
|
||
|
|
<p>If a simple command does not contain any slashes, <strong>
|
||
|
|
qsh</strong> finds the command by searching:</p>
|
||
|
|
|
||
|
|
<ol>
|
||
|
|
<li>for a special built-in utility of that name, then</li>
|
||
|
|
|
||
|
|
<li>for a shell function of that name, then</li>
|
||
|
|
|
||
|
|
<li>for a regular built-in utility of that name, then</li>
|
||
|
|
|
||
|
|
<li>each directory in the <strong>PATH</strong> variable in turn
|
||
|
|
for the regular utility.</li>
|
||
|
|
</ol>
|
||
|
|
|
||
|
|
<p>Command names containing a slash (<strong>/</strong>) are
|
||
|
|
run as a regular utility without performing any of the above
|
||
|
|
searches.</p>
|
||
|
|
|
||
|
|
<p><a name="builtin"></a>
|
||
|
|
A built-in utility is run internal to the shell, without
|
||
|
|
starting a new process. A special built-in utility is different
|
||
|
|
from a regular built-in utility in these respects:</p>
|
||
|
|
|
||
|
|
<ol>
|
||
|
|
<li>A syntax error in a special built-in utility causes a
|
||
|
|
non-interactive shell to exit.</li>
|
||
|
|
|
||
|
|
<li>Variable assignments specified with a special built-in utility
|
||
|
|
remain in effect after the utility completes.</li>
|
||
|
|
</ol>
|
||
|
|
|
||
|
|
<p>
|
||
|
|
These are the special built-in utilities: <a href="break.htm">
|
||
|
|
break</a>, <a href="colon.htm">colon</a>, <a href="continue.htm">
|
||
|
|
continue</a>, <a href="declare.htm">declare</a>,
|
||
|
|
<a href="dot.htm">dot</a>, <a href="eval.htm">
|
||
|
|
eval</a>, <a href="exec.htm">exec</a>, <a href="exit.htm">exit</a>,
|
||
|
|
<a href="export.htm">export</a>, <a href="local.htm">local</a>,
|
||
|
|
<a href="readonly.htm">readonly</a>, <a href="return.htm">return</a>,
|
||
|
|
<a href="set.htm">set</a>, <a href="shift.htm">shift</a>, <a href="source.htm">
|
||
|
|
source</a>, <a href="trap.htm">trap</a>, <a href="typeset.htm">
|
||
|
|
typeset</a>, and <a href="unset.htm">unset</a>.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<p>When a shell function is run, all of the shell positional
|
||
|
|
parameters (except the special parameter <strong>0</strong>, which
|
||
|
|
remains unchanged) are set to the arguments of the shell function.
|
||
|
|
The variables which are explicitly placed in the environment of the
|
||
|
|
command (by placing assignments to them before the function name)
|
||
|
|
are made local to the function and are set to the specified values.
|
||
|
|
The positional parameters are restored to their original values
|
||
|
|
when the shell function completes.</p>
|
||
|
|
|
||
|
|
<p><a name="regular"></a>
|
||
|
|
When a regular utility is run, <strong>qsh</strong> starts a new
|
||
|
|
process, passing the arguments and the environment to the program.
|
||
|
|
If the program is a shell script, <strong>qsh</strong> will
|
||
|
|
interpret the program in a subshell. <strong>qsh</strong> will
|
||
|
|
reinitialize itself in this case, so that the effect will be as if
|
||
|
|
a new shell had been invoked to handle the shell script.</p>
|
||
|
|
|
||
|
|
<p><strong>Command exit status</strong></p>
|
||
|
|
|
||
|
|
<p>Each command has an exit status that can influence the behavior
|
||
|
|
of other shell commands. By convention, a command exits with zero
|
||
|
|
for normal or success, and non-zero for failure, error, or a false
|
||
|
|
indication. The documentation for each command describes the exit
|
||
|
|
codes it returns and what they mean. The exit status can be one of
|
||
|
|
these values:</p>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>0 for success.</li>
|
||
|
|
|
||
|
|
<li>1 to 125 for failure.</li>
|
||
|
|
|
||
|
|
<li>126 when <strong>qsh</strong> finds the command but it is not
|
||
|
|
executable.</li>
|
||
|
|
|
||
|
|
<li>127 when <strong>qsh</strong> cannot find the command.</li>
|
||
|
|
|
||
|
|
<li>128 and above when the command is ended by a signal. The value
|
||
|
|
is 128 plus the signal number.</li>
|
||
|
|
</ul>
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
|