php-doc-en/reference/regex/reference.xml

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 <reference id="ref.regex">
  <title>Regular Expression Functions (POSIX Extended)</title>
  <titleabbrev>POSIX Regex</titleabbrev>

  <partintro>
   <section id="regex.intro">
    &reftitle.intro;
    <tip>
     <para>
      PHP also supports regular expressions using a Perl-compatible syntax
      using the <link linkend="ref.pcre">PCRE functions</link>. Those functions
      support non-greedy matching, assertions, conditional subpatterns, and a
      number of other features not supported by the POSIX-extended regular
      expression syntax.
     </para>
    </tip>
    <warning>
     <para>
      These regular expression functions are not binary-safe. The <link
      linkend="ref.pcre">PCRE functions</link> are.
     </para>
    </warning>
    <para>
     Regular expressions are used for complex string manipulation.
     PHP uses the POSIX extended regular expressions as defined by POSIX
     1003.2. For a full description of POSIX regular expressions see the regex
     man pages included in the regex directory in the PHP distribution. It's
     in manpage format, so you'll want to do something along the lines of
     <command>man /usr/local/src/regex/regex.7</command> in order to read it.
    </para>
   </section>
   
   <section id="regex.requirements">
    &reftitle.required;
    &no.requirement;
   </section>
   
   &reference.regex.configure;

   <section id="regex.configuration">
    &reftitle.runtime;
    &no.config;
   </section>

   <section id="regex.resources">
    &reftitle.resources;
    &no.resource;
   </section>

   <section id="regex.constants">
    &reftitle.constants;
    &no.constants;
   </section>

   <section id="regex.examples">
    &reftitle.examples;
    <para>
     <example>
     <title>Regular Expression Examples</title>
      <programlisting role="php">
<![CDATA[
<?php
// Returns true if "abc" is found anywhere in $string.
ereg("abc", $string);            

// Returns true if "abc" is found at the beginning of $string.
ereg("^abc", $string);

// Returns true if "abc" is found at the end of $string.
ereg("abc$", $string);

// Returns true if client browser is Netscape 2, 3 or MSIE 3.
eregi("(ozilla.[23]|MSIE.3)", $HTTP_USER_AGENT);  

// Places three space separated words into $regs[1], $regs[2] and $regs[3].
ereg("([[:alnum:]]+) ([[:alnum:]]+) ([[:alnum:]]+)", $string, $regs); 

// Put a <br /> tag at the beginning of $string.
$string = ereg_replace("^", "<br />", $string); 
 
// Put a <br /> tag at the end of $string.
$string = ereg_replace("$", "<br />", $string); 

// Get rid of any newline characters in $string.
$string = ereg_replace("\n", "", $string);
?>
]]>
      </programlisting>
     </example>
    </para>
   </section>

   <section id="regex.seealso">
    &reftitle.seealso;
    <para>
     For regular expressions in Perl-compatible syntax have a look at the
     <link linkend="ref.pcre">PCRE functions</link>. The simpler shell style
     wildcard pattern matching is provided by <function>fnmatch</function>.
    </para>
   </section>
  </partintro>

  &reference.regex.functions;

 </reference>
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