preg-match.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.preg-match" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>preg_match</refname>
  <refpurpose>Perform a regular expression match</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type class="union"><type>int</type><type>false</type></type><methodname>preg_match</methodname>
   <methodparam><type>string</type><parameter>pattern</parameter></methodparam>
   <methodparam><type>string</type><parameter>subject</parameter></methodparam>
   <methodparam choice="opt"><type>array</type><parameter role="reference">matches</parameter><initializer>&null;</initializer></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>flags</parameter><initializer>0</initializer></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>offset</parameter><initializer>0</initializer></methodparam>
  </methodsynopsis>
  <para>
   Searches <parameter>subject</parameter> for a match to the regular
   expression given in <parameter>pattern</parameter>.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>pattern</parameter></term>
     <listitem>
      <para>
       The pattern to search for, as a string.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>subject</parameter></term>
     <listitem>
      <para>
       The input string.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>matches</parameter></term>
     <listitem>
      <para>
       If <parameter>matches</parameter> is provided, then it is filled with
       the results of search. <varname>$matches[0]</varname> will contain the
       text that matched the full pattern, <varname>$matches[1]</varname>
       will have the text that matched the first captured parenthesized
       subpattern, and so on.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>flags</parameter></term>
     <listitem>
      <para>
       <parameter>flags</parameter> can be a combination of the following flags:
       <variablelist>
        <varlistentry>
         <term><constant>PREG_OFFSET_CAPTURE</constant></term>
         <listitem>
          <para>
           If this flag is passed, for every occurring match the appendant string
           offset (in bytes) will also be returned. Note that this changes the value of
           <parameter>matches</parameter> into an array where every element is an
           array consisting of the matched string at offset <literal>0</literal>
           and its string offset into <parameter>subject</parameter> at offset
           <literal>1</literal>.
           <informalexample>
            <programlisting role="php">
<![CDATA[
<?php
preg_match('/(foo)(bar)(baz)/', 'foobarbaz', $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>
]]>
            </programlisting>
            &example.outputs;
            <screen>
<![CDATA[
Array
(
    [0] => Array
        (
            [0] => foobarbaz
            [1] => 0
        )

    [1] => Array
        (
            [0] => foo
            [1] => 0
        )

    [2] => Array
        (
            [0] => bar
            [1] => 3
        )

    [3] => Array
        (
            [0] => baz
            [1] => 6
        )

)
]]>
            </screen>
           </informalexample>
          </para>
         </listitem>
        </varlistentry>
        <varlistentry>
         <term><constant>PREG_UNMATCHED_AS_NULL</constant></term>
         <listitem>
          <para>
           If this flag is passed, unmatched subpatterns are reported as &null;;
           otherwise they are reported as an empty <type>string</type>.
           <informalexample>
            <programlisting role="php">
<![CDATA[
<?php
preg_match('/(a)(b)*(c)/', 'ac', $matches);
var_dump($matches);
preg_match('/(a)(b)*(c)/', 'ac', $matches, PREG_UNMATCHED_AS_NULL);
var_dump($matches);
?>
]]>
            </programlisting>
            &example.outputs;
            <screen>
<![CDATA[
array(4) {
  [0]=>
  string(2) "ac"
  [1]=>
  string(1) "a"
  [2]=>
  string(0) ""
  [3]=>
  string(1) "c"
}
array(4) {
  [0]=>
  string(2) "ac"
  [1]=>
  string(1) "a"
  [2]=>
  NULL
  [3]=>
  string(1) "c"
}
]]>
            </screen>
           </informalexample>
          </para>
         </listitem>
        </varlistentry>
       </variablelist>
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>offset</parameter></term>
     <listitem>
      <para>
       Normally, the search starts from the beginning of the subject string.
       The optional parameter <parameter>offset</parameter> can be used to
       specify the alternate place from which to start the search (in bytes).
      </para>
      <note>
       <para>
        Using <parameter>offset</parameter> is not equivalent to passing
        <code>substr($subject, $offset)</code> to
        <function>preg_match</function> in place of the subject string,
        because <parameter>pattern</parameter> can contain assertions such as
        <emphasis>^</emphasis>, <emphasis>$</emphasis> or
        <emphasis>(?&lt;=x)</emphasis>. Compare:
        <informalexample>
         <programlisting role="php">
<![CDATA[
<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, $subject, $matches, PREG_OFFSET_CAPTURE, 3);
print_r($matches);
?>
]]>
         </programlisting>
         &example.outputs;
         <screen>
<![CDATA[
Array
(
)
]]>
         </screen>
         <para>
          while this example
         </para>
         <programlisting role="php">
<![CDATA[
<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, substr($subject,3), $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>
]]>
         </programlisting>
         <para>
          will produce
         </para>
         <screen>
<![CDATA[
Array
(
    [0] => Array
        (
            [0] => def
            [1] => 0
        )

)
]]>
         </screen>
         <para>
          Alternatively, to avoid using <function>substr</function>, use the
          <literal>\G</literal> assertion rather than the <literal>^</literal> anchor, or
          the <literal>A</literal> modifier instead, both of which work with
          the <parameter>offset</parameter> parameter.
         </para>
        </informalexample>
       </para>
      </note>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   <function>preg_match</function> returns 1 if the <parameter>pattern</parameter>
   matches given <parameter>subject</parameter>, 0 if it does not,&return.falseforfailure;.
  </para>
  &return.falseproblem;
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  &pcre.pattern.warning;
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>7.2.0</entry>
       <entry>
        The <constant>PREG_UNMATCHED_AS_NULL</constant> is now supported for the
        <parameter>$flags</parameter> parameter.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>Find the string of text "php"</title>
    <programlisting role="php">
<![CDATA[
<?php
// The "i" after the pattern delimiter indicates a case-insensitive search
if (preg_match("/php/i", "PHP is the web scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>Find the word "web"</title>
    <programlisting role="php">
<![CDATA[
<?php
/* The \b in the pattern indicates a word boundary, so only the distinct
 * word "web" is matched, and not a word partial like "webbing" or "cobweb" */
if (preg_match("/\bweb\b/i", "PHP is the web scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}

echo "\n";

if (preg_match("/\bweb\b/i", "PHP is the website scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>Getting the domain name out of a URL</title>
    <programlisting role="php">
<![CDATA[
<?php
// get host name from URL
preg_match('@^(?:http://)?([^/]+)@i',
    "http://www.php.net/index.html", $matches);
$host = $matches[1];

// get last two segments of host name
preg_match('/[^.]+\.[^.]+$/', $host, $matches);
echo "domain name is: {$matches[0]}\n";
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
domain name is: php.net
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title>Using named subpattern</title>
    <programlisting role="php">
<![CDATA[
<?php

$str = 'foobar: 2008';

preg_match('/(?P<name>\w+): (?P<digit>\d+)/', $str, $matches);

/* Alternative */
// preg_match('/(?<name>\w+): (?<digit>\d+)/', $str, $matches);

print_r($matches);

?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
Array
(
    [0] => foobar: 2008
    [name] => foobar
    [1] => foobar
    [digit] => 2008
    [2] => 2008
)
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <tip>
   <para>
    Do not use <function>preg_match</function> if you only want to check if
    one string is contained in another string. Use
    <function>strpos</function> instead as it will be faster.
   </para>
  </tip>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><link linkend="pcre.pattern">PCRE Patterns</link></member>
    <member><function>preg_quote</function></member>
    <member><function>preg_match_all</function></member>
    <member><function>preg_replace</function></member>
    <member><function>preg_split</function></member>
    <member><function>preg_last_error</function></member>
    <member><function>preg_last_error_msg</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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