php-doc-en/functions/regex.xml

 <reference id="ref.regex">
  <title>Regular expression functions</title>
  <titleabbrev>Regexps</titleabbrev>
  <partintro>
   <para>
    Regular expressions are used for complex string manipulation in
    PHP. The functions that support regular expressions are:

    <itemizedlist>
     <listitem>
      <simpara><function>ereg</function></simpara>
     </listitem>
     <listitem>
      <simpara><function>ereg_replace</function></simpara>
     </listitem>
     <listitem>
      <simpara><function>eregi</function></simpara>
     </listitem>
     <listitem>
      <simpara><function>eregi_replace</function></simpara>
     </listitem>
     <listitem>
      <simpara><function>split</function></simpara>
     </listitem>
    </itemizedlist>

    These functions all take a regular expression string as their
    first argument.  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.

   <!-- Should add discussion of PCRE functions here. --></para>

   <para>
    <example>
     <title>Regular expression examples</title>
     <programlisting>
ereg(&quot;abc&quot;,$string);            
/* Returns true if &quot;abc&quot;
   is found anywhere in $string. */

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

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

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

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

$string = ereg_replace("^","&lt;BR&gt;",$string); 
/* Put a &lt;BR&gt; tag at the beginning of $string. */
 
$string = ereg_replace("$","&lt;BR&gt;",$string); 
/* Put a &lt;BR&gt; tag at the end of $string. */

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

  </partintro>

  <refentry id="function.ereg">
   <refnamediv>
    <refname>ereg</refname>
    <refpurpose>regular expression match</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>int <function>ereg</function></funcdef>
     <paramdef>string <parameter>pattern</parameter></paramdef>
     <paramdef>string <parameter>string</parameter></paramdef>
     <paramdef>array <parameter><optional>regs</optional></parameter></paramdef>
    </funcsynopsis>
    <simpara>
     Searchs <parameter>string</parameter> for matches to the regular expression
     given in <parameter>pattern</parameter>.</simpara> 

    <simpara>
     If matches are found for parenthesized substrings of
     <parameter>pattern</parameter> and the function is called with
     the third argument <parameter>regs</parameter>, the matches will
     be stored in the elements of
     <parameter>regs</parameter>. $regs[1] will contain the substring
     which starts at the first left parenthesis; $regs[2] will contain the
     substring starting at the second, and so on. $regs[0] will
     contain a copy of <parameter>string</parameter>.</simpara>

    <para>
     Searching is case sensitive.</para>

    <para>
     Returns true if a match for pattern was found in string, or false
     if no matches were found or an error occurred.</para>
    
    <para>
     The following code snippet takes a date in ISO format (YYYY-MM-DD)
     and prints it in DD.MM.YYYY format:
     <example>
      <title>ereg() example</title>
      <programlisting>
if ( ereg( "([0-9]{4})-([0-9]{1,2})-([0-9]{1,2})", $date, $regs ) ) {
    echo "$regs[3].$regs[2].$regs[1]";
} else {
    echo "Invalid date format: $date";
}
</programlisting></example></para>

    <para>
     See also <function>eregi</function>, <function>ereg_replace</function>, and <function>eregi_replace</function>.</para>

   </refsect1>
  </refentry>


  <refentry id="function.ereg-replace">
   <refnamediv>
    <refname>ereg_replace</refname>
    <refpurpose>replace regular expression</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>string <function>ereg_replace</function></funcdef>
     <paramdef>string <parameter>pattern</parameter></paramdef>
     <paramdef>string <parameter>replacement</parameter></paramdef>
     <paramdef>string <parameter>string</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function scans <parameter>string</parameter> for matches to
     <parameter>pattern</parameter>, then replaces the matched text
     with <parameter>replacement</parameter>.</para>

    <para>
     The modified string is returned. (Which may mean that the
     original string is returned if there are no matches to be
     replaced.)</para>

    <para>
     If <parameter>pattern</parameter> contains parenthesized
     substrings, <parameter>replacement</parameter> may contain
     substrings of the form
     <literal>\\<replaceable>digit</replaceable></literal>, which will
     be replaced by the text matching the digit'th parenthesized
     substring; <literal>\\0</literal> will produce the entire
     contents of string.  Up to nine substrings may be used.
     Parentheses may be nested, in which case they are counted by the
     opening parenthesis.</para>  

    <para>
     If no matches are found in <parameter>string</parameter>, then
     <parameter>string</parameter> will be returned unchanged.</para>

    <para>
     For example, the following code snippet
     prints "This was a test" three times:
     <example>
      <title>ereg_replace() example</title>
      <programlisting>
$string = "This is a test";
echo ereg_replace( " is", " was", $string );
echo ereg_replace( "( )is", "\\1was", $string );
echo ereg_replace( "(( )is)", "\\2was", $string );
      </programlisting>
     </example></para>

    <para>
     See also <function>ereg</function>, <function>eregi</function>,
     and <function>eregi_replace</function>.</para>
   </refsect1>
  </refentry>


  <refentry id="function.eregi">
   <refnamediv>
    <refname>eregi</refname>
    <refpurpose>case insensitive regular expression match</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>int <function>eregi</function></funcdef>
     <paramdef>string <parameter>pattern</parameter></paramdef>
     <paramdef>string <parameter>string</parameter></paramdef>
     <paramdef>array <parameter><optional>regs</optional></parameter></paramdef>
    </funcsynopsis>
    <para>
     This function is identical to <function>ereg</function> save that this ignores
     case distinction when matching alphabetic characters.</para>

    <para>
     See also <function>ereg</function>, <function>ereg_replace</function>, and <function>eregi_replace</function>.</para>
  
   </refsect1>
  </refentry>


  <refentry id="function.eregi-replace">
   <refnamediv>
    <refname>eregi_replace</refname>
    <refpurpose>replace regular expression case insensitive</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>string <function>eregi_replace</function></funcdef>
     <paramdef>string <parameter>pattern</parameter></paramdef>
     <paramdef>string <parameter>replacement</parameter></paramdef>
     <paramdef>string <parameter>string</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function is identical to <function>ereg_replace</function> save that
     this ignores case distinction when matching alphabetic characters.</para>

    <para>
     See also <function>ereg</function>, <function>eregi</function>, and <function>ereg_replace</function>.</para>

   </refsect1>
  </refentry>


  <refentry id="function.split">
   <refnamediv>
    <refname>split</refname>
    <refpurpose>split string into array by regular expression</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>split</function></funcdef>
     <paramdef>string <parameter>pattern</parameter></paramdef>
     <paramdef>string <parameter>string</parameter></paramdef>
     <paramdef>int <parameter><optional>limit</optional></parameter></paramdef>
    </funcsynopsis>
    <para>
     Returns an array of strings, each of which is a substring of
     <parameter>string</parameter> formed by splitting it on boundaries formed 
     by the regular expression <parameter>pattern</parameter>. 
		 If <parameter>limit</parameter> is set, the returned array will contaion a 
     maximum of <parameter>limit</parameter> elements with the last element
     containing the whole rest of <parameter>string</parameter>.
     If an error occurs, <function>split</function> returns false.
    </para>

    <para>
     To get the first five fields from a line from
     <filename>/etc/passwd</filename>:
	 <example>
      <title>split() example</title>
      <programlisting>
$passwd_list = split( ":", $passwd_line, 5 );
	  </programlisting>
	 </example>
	</para>

    <para>
	 To parse a date which may be delimited with slashes, dots, or
	 hyphens:
	 <example>
      <title>split() example</title>
      <programlisting>
$date = "04/30/1973";  // Delimiters may be slash, dot, or hyphen
list( $month, $day, $year ) = split( '[/.-]', $date );
echo "Month: $month; Day: $day; Year: $year&lt;br&gt;\n";
	  </programlisting>
	 </example>
	</para>

    <para>
     Note that <parameter>pattern</parameter> is case-sensitive.
	</para>

	<para>
	 Note that if you don't require the power of regular expressions,
	 it is faster to use <function>explode</function>, which doesn't
	 incur the overhead of the regular expression engine.
	</para>

	<para>
	 Please note that <parameter>pattern</parameter> is a regular
	 expression.  If you want to split on any of the characters which
	 are considered special by regular expressions, you'll need to
	 escape them first. If you think <function>split</function> (or
	 any other regex function, for that matter) is doing something
	 weird, please read the file <filename>regex.7</filename>,
	 included in the <filename>regex/</filename> subdirectory of 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>

    <para>
     See also: <function>explode</function> and <function>implode</function>.
	</para>

   </refsect1>
  </refentry>


  <refentry id="function.sql-regcase">
   <refnamediv>
    <refname>sql_regcase</refname>
    <refpurpose>make regular expression for case insensitive match</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>string <function>sql_regcase</function></funcdef>
     <paramdef>string <parameter>string</parameter></paramdef>
    </funcsynopsis>
    <para>
     Returns a valid regular expression which will match <parameter>string</parameter>,
     ignoring case. This expression is <parameter>string</parameter> with each character
     converted to a bracket expression; this bracket expression
     contains that character's uppercase and lowercase form if
     applicable, otherwise it contains the original character
     twice.
     <example>
      <title>sql_regcase() example</title>
      <programlisting>
echo sql_regcase( "Foo bar" );
</programlisting></example>

     prints <screen>[Ff][Oo][Oo][  ][Bb][Aa][Rr]</screen>.</para>

    <para>
     This can be used to achieve case insensitive pattern matching in
     products which support only case sensitive regular expressions.</para>
  
   </refsect1>
  </refentry>


 </reference>

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