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  <refentry id="function.system">
   <refnamediv>
    <refname>system</refname>
    <refpurpose>Execute an external program and display output</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>string</type><methodname>system</methodname>
      <methodparam><type>string</type><parameter>command</parameter></methodparam>
      <methodparam choice="opt"><type>int</type><parameter>return_var</parameter></methodparam>
     </methodsynopsis>
    <para>
     <function>system</function> is just like the C version of the
     function in that it executes the given
     <parameter>command</parameter> and outputs the result.  If a
     variable is provided as the second argument, then the return
     status code of the executed command will be written to this
     variable.
    </para>
    <warning>
     <para>
      If you are going to allow data coming from user input to be passed to
      this function, then you should be using
      <function>escapeshellarg</function> or
      <function>escapeshellcmd</function> to make sure that users cannot trick
      the system into executing arbitrary commands.
     </para>
    </warning>
    <note>
     <para>
      If you start a program using this function and want to leave it running
      in the background, you have to make sure that the output of that program
      is redirected to a file or some other output stream or else PHP will
      hang until the execution of the program ends.
     </para>
    </note>
    <para>
     The <function>system</function> call also tries to automatically
     flush the web server's output buffer after each line of output if
     PHP is running as a server module.
    </para>
    <para>
     Returns the last line of the command output on success, and &false;
     on failure.
    </para>
    <para>
     If you need to execute a command and have all the data from the
     command passed directly back without any interference, use the
     <function>passthru</function> function.
    </para>
    <para>
     <example>
      <title><function>system</function> example</title>
      <programlisting role="php">
<![CDATA[
<?php
echo '<pre>';

// Outputs all the result of shellcommand "ls", and returns
// the last output line into $last_line. Stores the return value
// of the shell command in $retval.
$last_line = system('ls', $retval);

// Printing additional info
echo '
</pre>
<hr>Last line of the output: '.$last_line.'
<hr>Return value: '.$retval;
?>
]]>
      </programlisting>
     </example>
    </para>
    <para>
     See also <function>exec</function>,
     <function>passthru</function>, <function>popen</function>,
     <function>escapeshellcmd</function>, and the <link
     linkend="language.operators.execution">backtick operator</link>.
    </para>
   </refsect1>
  </refentry>

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