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<refentry xml:id="function.popen" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>popen</refname>
  <refpurpose>Opens process file pointer</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type class="union"><type>resource</type><type>false</type></type><methodname>popen</methodname>
   <methodparam><type>string</type><parameter>command</parameter></methodparam>
   <methodparam><type>string</type><parameter>mode</parameter></methodparam>
  </methodsynopsis>
  <para>
   Opens a pipe to a process executed by forking the command given
   by <parameter>command</parameter>.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>command</parameter></term>
     <listitem>
      <para>
       The command
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>mode</parameter></term>
     <listitem>
      <para>
       The mode. Either <literal>'r'</literal> for reading, or <literal>'w'</literal>
       for writing.
      </para>
      <para>
       On Windows, <function>popen</function> defaults to text mode, i.e. any <literal>\n</literal>
       characters written to or read from the pipe will be translated to <literal>\r\n</literal>.
       If this is not desired, binary mode can be enforced by setting <parameter>mode</parameter>
       to <literal>'rb'</literal> and <literal>'wb'</literal>, respectively.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>
 
 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns a file pointer identical to that returned by
   <function>fopen</function>, except that it is unidirectional (may
   only be used for reading or writing) and must be closed with
   <function>pclose</function>. This pointer may be used with
   <function>fgets</function>, <function>fgetss</function>, and
   <function>fwrite</function>. When the mode is 'r', the returned
   file pointer equals to the STDOUT of the command, when the mode
   is 'w', the returned file pointer equals to the STDIN of the
   command.
  </para>
  <para>
   If an error occurs, returns &false;.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>popen</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
$handle = popen("/bin/ls", "r");
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   If the command to be executed could not be found, a valid
   resource is returned. This may seem odd, but makes sense; it
   allows you to access any error message returned by the shell:
   <example>
    <title><function>popen</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
error_reporting(E_ALL);

/* Add redirection so we can get stderr. */
$handle = popen('/path/to/executable 2>&1', 'r');
echo "'$handle'; " . gettype($handle) . "\n";
$read = fread($handle, 2096);
echo $read;
pclose($handle);
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>
 
 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    If you're looking for bi-directional support (two-way), use
    <function>proc_open</function>.
   </para>
  </note>
 </refsect1>
 
 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>pclose</function></member>
    <member><function>fopen</function></member>
    <member><function>proc_open</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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