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<h1>system</h1>
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Perl 5 version 10.1 documentation
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system
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<h1>system</h1>
<div class="mod_az_list">
<a href="../index-functions.html">Perl functions A-Z</a> |
<a href="../index-functions-by-cat.html">Perl functions by category</a> |
<a href="../perlfunc.html">The 'perlfunc' manpage</a>
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<!-- -->
<ul>
<li><a name="system-LIST"></a><b>system LIST</b>
<p> </p>
</li>
</ul>
<ul>
<li><a name="system-PROGRAM-LIST"></a><b>system PROGRAM LIST</b>
<p>Does exactly the same thing as <code class="inline"><a class="l_k" href="../functions/exec.html">exec</a> <span class="i">LIST</span></code>
, except that a fork is
done first, and the parent process waits for the child process to
complete. Note that argument processing varies depending on the
number of arguments. If there is more than one argument in LIST,
or if LIST is an array with more than one value, starts the program
given by the first element of the list with arguments given by the
rest of the list. If there is only one scalar argument, the argument
is checked for shell metacharacters, and if there are any, the
entire argument is passed to the system's command shell for parsing
(this is <code class="inline">/bin/sh -c</code> on Unix platforms, but varies on other
platforms). If there are no shell metacharacters in the argument,
it is split into words and passed directly to <code class="inline"><span class="w">execvp</span></code>
, which is
more efficient.</p>
<p>Beginning with v5.6.0, Perl will attempt to flush all files opened for
output before any operation that may do a fork, but this may not be
supported on some platforms (see <a href="../perlport.html">perlport</a>). To be safe, you may need
to set <code class="inline"><span class="i">$|</span></code>
($AUTOFLUSH in English) or call the <code class="inline"><span class="i">autoflush</span><span class="s">(</span><span class="s">)</span></code>
method
of <code class="inline"><span class="w">IO::Handle</span></code>
on any open handles.</p>
<p>The return value is the exit status of the program as returned by the
<code class="inline"><a class="l_k" href="../functions/wait.html">wait</a></code> call. To get the actual exit value, shift right by eight (see
below). See also <a href="../functions/exec.html">"exec"</a>. This is <i>not</i> what you want to use to capture
the output from a command, for that you should use merely backticks or
<code class="inline"><a class="l_k" href="../functions/qx.html">qx//</a></code>, as described in <a href="../perlop.html#%60STRING%60">"`STRING`" in perlop</a>. Return value of -1
indicates a failure to start the program or an error of the wait(2) system
call (inspect $! for the reason).</p>
<p>If you'd like to make <code class="inline"><a class="l_k" href="../functions/system.html">system</a></code> (and many other bits of Perl) die on error,
have a look at the <a href="../autodie.html">autodie</a> pragma.</p>
<p>Like <code class="inline"><a class="l_k" href="../functions/exec.html">exec</a></code>, <code class="inline"><a class="l_k" href="../functions/system.html">system</a></code> allows you to lie to a program about its name if
you use the <code class="inline"><a class="l_k" href="../functions/system.html">system</a> <span class="i">PROGRAM</span> <span class="w">LIST</span></code>
syntax. Again, see <a href="../functions/exec.html">"exec"</a>.</p>
<p>Since <code class="inline"><span class="w">SIGINT</span></code>
and <code class="inline"><span class="w">SIGQUIT</span></code>
are ignored during the execution of
<code class="inline"><a class="l_k" href="../functions/system.html">system</a></code>, if you expect your program to terminate on receipt of these
signals you will need to arrange to do so yourself based on the return
value.</p>
<pre class="verbatim"><ol><li> <span class="i">@args</span> = <span class="s">(</span><span class="q">"command"</span><span class="cm">,</span> <span class="q">"arg1"</span><span class="cm">,</span> <span class="q">"arg2"</span><span class="s">)</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/system.html">system</a><span class="s">(</span><span class="i">@args</span><span class="s">)</span> == <span class="n">0</span></li><li> or <a class="l_k" href="../functions/die.html">die</a> <span class="q">"system @args failed: $?"</span></li></ol></pre><p>If you'd like to manually inspect <code class="inline"><a class="l_k" href="../functions/system.html">system</a></code>'s failure, you can check all
possible failure modes by inspecting <code class="inline"><span class="i">$?</span></code>
like this:</p>
<pre class="verbatim"><ol><li> if <span class="s">(</span><span class="i">$?</span> == <span class="n">-1</span><span class="s">)</span> <span class="s">{</span></li><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"failed to execute: $!\n"</span><span class="sc">;</span></li><li> <span class="s">}</span></li><li> elsif <span class="s">(</span><span class="i">$?</span> & <span class="n">127</span><span class="s">)</span> <span class="s">{</span></li><li> <a class="l_k" href="../functions/printf.html">printf</a> <span class="q">"child died with signal %d, %s coredump\n"</span><span class="cm">,</span></li><li> <span class="s">(</span><span class="i">$?</span> & <span class="n">127</span><span class="s">)</span><span class="cm">,</span> <span class="s">(</span><span class="i">$?</span> & <span class="n">128</span><span class="s">)</span> ? <span class="q">'with'</span> <span class="co">:</span> <span class="q">'without'</span><span class="sc">;</span></li><li> <span class="s">}</span></li><li> else <span class="s">{</span></li><li> <a class="l_k" href="../functions/printf.html">printf</a> <span class="q">"child exited with value %d\n"</span><span class="cm">,</span> <span class="i">$?</span> >> <span class="n">8</span><span class="sc">;</span></li><li> <span class="s">}</span></li></ol></pre><p>Alternatively you might inspect the value of <code class="inline"><span class="i">$</span>{<span class="w">^CHILD_ERROR_NATIVE</span>}</code>
with the W*() calls of the POSIX extension.</p>
<p>When the arguments get executed via the system shell, results
and return codes will be subject to its quirks and capabilities.
See <a href="../perlop.html#%60STRING%60">"`STRING`" in perlop</a> and <a href="../functions/exec.html">"exec"</a> for details.</p>
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