<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.18 $ -->
<!-- splitted from ./en/functions/pcre.xml, last change in rev 1.2 -->
<refentry id="function.preg-replace">
 <refnamediv>
  <refname>preg_replace</refname>
  <refpurpose>Perform a regular expression search and replace</refpurpose>
 </refnamediv>
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>mixed</type><methodname>preg_replace</methodname>
   <methodparam><type>mixed</type><parameter>pattern</parameter></methodparam>
   <methodparam><type>mixed</type><parameter>replacement</parameter></methodparam>
   <methodparam><type>mixed</type><parameter>subject</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>limit</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter role="reference">count</parameter></methodparam>
  </methodsynopsis>
  <para>
   Searches <parameter>subject</parameter> for matches to
   <parameter>pattern</parameter> and replaces them with
   <parameter>replacement</parameter>.
  </para>
  <para>
   <parameter>Replacement</parameter> may contain references of the form
   <literal>\\<replaceable>n</replaceable></literal> or (since PHP 4.0.4)
   <literal><replaceable>$n</replaceable></literal>, with the latter form
   being the preferred one. Every such reference will be replaced by the text
   captured by the <replaceable>n</replaceable>'th parenthesized pattern.
   <replaceable>n </replaceable>can be from 0 to 99, and
   <literal>\\0</literal> or <literal>$0</literal> refers to the text matched
   by the whole pattern. Opening parentheses are counted from left to right
   (starting from 1) to obtain the number of the capturing subpattern.
  </para>
  <para>
   When working with a replacement pattern where a backreference is immediately
   followed by another number (i.e.: placing a literal number immediately
   after a matched pattern), you cannot use the familiar <literal>\\1</literal>
   notation for your backreference.  <literal>\\11</literal>, for example,
   would confuse <function>preg_replace</function> since it does not know whether
   you want the <literal>\\1</literal> backreference followed by a literal <literal>1</literal>, 
   or the <literal>\\11</literal> backreference followed by nothing.  In this case
   the solution is to use <literal>\${1}1</literal>.  This creates an
   isolated <literal>$1</literal> backreference, leaving the <literal>1</literal>
   as a literal.
  </para>
  <para>
   If <parameter>subject</parameter> is an array, then the search
   and replace is performed on every entry of
   <parameter>subject</parameter>, and the return value is an array
   as well.
  </para>
  <para>
   The <literal>e</literal> modifier makes <function>preg_replace</function>
   treat the <parameter>replacement</parameter> parameter as PHP code after
   the appropriate references substitution is done. Tip: make sure that
   <parameter>replacement</parameter> constitutes a valid PHP code string,
   otherwise PHP will complain about a parse error at the line containing
   <function>preg_replace</function>.
  </para>
</refsect1>

<refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>pattern</parameter></term>
     <listitem>
      <para>
       The pattern to search for. It can be either a string or an array with
       strings.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>replacement</parameter></term>
     <listitem>
      <para>
       The string or an array with strings to replace. If this parameter is a
       string and the <parameter>pattern</parameter> parameter is an array,
       all patterns will be replaced by that string. If both
       <parameter>pattern</parameter> and <parameter>replacement</parameter>
       parameters are arrays, each <parameter>pattern</parameter> will be
       replaced by the <parameter>replacement</parameter> counterpart. If
       there are fewer elements in the <parameter>replacement</parameter>
       array than in the <parameter>pattern</parameter> array, any extra
       <parameter>pattern</parameter>s will be replaced by an empty string.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>subject</parameter></term>
     <listitem>
      <para>
       The string or an array with strings to search and replace.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>limit</parameter></term>
     <listitem>
      <para>
       The maximum possible replacements for each pattern in each
       <parameter>subject</parameter> string. Defaults to
       <literal>-1</literal> (no limit).
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>count</parameter></term>
     <listitem>
      <para>
       If specified, this variable will be filled with the number of
       replacements done.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   <function>preg_replace</function> returns an array if the
   <parameter>subject</parameter> parameter is an array, or a string
   otherwise.
  </para>
  <para>
   If matches are found, the new <parameter>subject</parameter> will
   be returned, otherwise <parameter>subject</parameter> will be
   returned unchanged.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>4.0.1pl2</entry>
       <entry>
        Added the <parameter>limit</parameter> parameter
       </entry>
      </row>
      <row>
       <entry>4.0.4</entry>
       <entry>
        Added the '$n' form for the <parameter>replacement</parameter> parameter
       </entry>
      </row>
      <row>
       <entry>5.1.0</entry>
       <entry>
        Added the <parameter>count</parameter> parameter
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>Using backreferences followed by numeric literals</title>
    <programlisting role="php">
<![CDATA[
<?php
$string = 'April 15, 2003';
$pattern = '/(\w+) (\d+), (\d+)/i';
$replacement = '${1}1,$3';
echo preg_replace($pattern, $replacement, $string);
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
April1,2003
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title>Using indexed arrays with <function>preg_replace</function></title>
    <programlisting role="php">
<![CDATA[
<?php
$string = 'The quick brown fox jumped over the lazy dog.';
$patterns[0] = '/quick/';
$patterns[1] = '/brown/';
$patterns[2] = '/fox/';
$replacements[2] = 'bear';
$replacements[1] = 'black';
$replacements[0] = 'slow';
echo preg_replace($patterns, $replacements, $string);
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
The bear black slow jumped over the lazy dog.
]]>
    </screen>
    <para>
     By ksorting patterns and replacements, we should get what we wanted.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
ksort($patterns);
ksort($replacements);
echo preg_replace($patterns, $replacements, $string);
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
The slow black bear jumped over the lazy dog.
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title>Replacing several values</title>
    <programlisting role="php">
<![CDATA[
<?php
$patterns = array ('/(19|20)(\d{2})-(\d{1,2})-(\d{1,2})/',
                   '/^\s*{(\w+)}\s*=/');
$replace = array ('\3/\4/\1\2', '$\1 =');
echo preg_replace($patterns, $replace, '{startDate} = 1999-5-27');
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
$startDate = 5/27/1999
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title>Using the 'e' modifier</title>
    <programlisting role="php">
<![CDATA[
<?php
preg_replace("/(<\/?)(\w+)([^>]*>)/e", 
             "'\\1'.strtoupper('\\2').'\\3'", 
             $html_body);
?>
]]>
    </programlisting>
    <para>
     This would capitalize all HTML tags in the input text.
    </para>
   </example>
  </para>
  <para>
   <example>
    <title>Strip whitespace</title>
    <para>
     This example strips excess whitespace from a string.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
$str = 'foo   o';
$str = preg_replace('/\s\s+/', ' ', $str);
// This will be 'foo o' now
echo $str;
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>Using the <parameter>count</parameter> parameter</title>
    <programlisting role="php">
<![CDATA[
<?php
$count = 0;

echo preg_replace(array('/\d/', '/\s/'), '*', 'xp 4 to', -1 , $count);
echo $count; //3
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
xp***to
3
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    When using arrays with <parameter>pattern</parameter> and
    <parameter>replacement</parameter>, the keys are processed in the order
    they appear in the array. This is <emphasis>not necessarily</emphasis> the
    same as the numerical index order. If you use indexes to identify which
    <parameter>pattern</parameter> should be replaced by which
    <parameter>replacement</parameter>, you should perform a
    <function>ksort</function> on each array prior to calling
    <function>preg_replace</function>.
   </para>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>preg_match</function></member>
    <member><function>preg_replace_callback</function></member>
    <member><function>preg_split</function></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>

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