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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@43188 c90b9560-bf6c-de11-be94-00142212c4b1
463 lines
15 KiB
XML
463 lines
15 KiB
XML
<reference id="ref.regex">
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<title>Regular Expression Functions (POSIX Extended)</title>
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<titleabbrev>Regexps</titleabbrev>
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<partintro>
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<para>
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Regular expressions are used for complex string manipulation in
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PHP. The functions that support regular expressions are:
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<itemizedlist>
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<listitem>
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<simpara><function>ereg</function></simpara>
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</listitem>
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<listitem>
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<simpara><function>ereg_replace</function></simpara>
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</listitem>
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<listitem>
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<simpara><function>eregi</function></simpara>
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</listitem>
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<listitem>
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<simpara><function>eregi_replace</function></simpara>
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</listitem>
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<listitem>
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<simpara><function>split</function></simpara>
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</listitem>
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<listitem>
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<simpara><function>spliti</function></simpara>
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</listitem>
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</itemizedlist>
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These functions all take a regular expression string as their
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first argument. PHP uses the POSIX extended regular expressions
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as defined by POSIX 1003.2. For a full description of POSIX
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regular expressions see the regex man pages included in the regex
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directory in the PHP distribution. It's in manpage format, so
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you'll want to do something along the lines of <command>man
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/usr/local/src/regex/regex.7</command> in order to read it.
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<!-- Should add discussion of PCRE functions here. -->
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</para>
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<para>
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<example>
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<title>Regular Expression Examples</title>
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<programlisting role="php">
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ereg ("abc", $string);
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/* Returns true if "abc"
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is found anywhere in $string. */
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ereg ("^abc", $string);
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/* Returns true if "abc"
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is found at the beginning of $string. */
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ereg ("abc$", $string);
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/* Returns true if "abc"
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is found at the end of $string. */
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eregi ("(ozilla.[23]|MSIE.3)", $HTTP_USER_AGENT);
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/* Returns true if client browser
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is Netscape 2, 3 or MSIE 3. */
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ereg ("([[:alnum:]]+) ([[:alnum:]]+) ([[:alnum:]]+)", $string,$regs);
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/* Places three space separated words
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into $regs[1], $regs[2] and $regs[3]. */
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$string = ereg_replace ("^", "<BR>", $string);
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/* Put a <BR> tag at the beginning of $string. */
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$string = ereg_replace ("$", "<BR>", $string);
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/* Put a <BR> tag at the end of $string. */
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$string = ereg_replace ("\n", "", $string);
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/* Get rid of any newline
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characters in $string. */
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</programlisting>
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</example>
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</para>
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</partintro>
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<refentry id="function.ereg">
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<refnamediv>
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<refname>ereg</refname>
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<refpurpose>Regular expression match</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ereg</function></funcdef>
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<paramdef>string <parameter>pattern</parameter></paramdef>
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<paramdef>string <parameter>string</parameter></paramdef>
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<paramdef>array
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<parameter><optional>regs</optional></parameter>
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</paramdef>
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</funcprototype>
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</funcsynopsis>
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<simpara>
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Searches a <parameter>string</parameter> for matches to the regular
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expression given in <parameter>pattern</parameter>.
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</simpara>
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<simpara>
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If matches are found for parenthesized substrings of
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<parameter>pattern</parameter> and the function is called with
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the third argument <parameter>regs</parameter>, the matches will
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be stored in the elements of the array
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<parameter>regs</parameter>. $regs[1] will contain the substring
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which starts at the first left parenthesis; $regs[2] will contain
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the substring starting at the second, and so on. $regs[0] will
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contain a copy of <parameter>string</parameter>.
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</simpara>
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<simpara>
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If <function>ereg</function> finds any matches at all, $regs will
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be filled with exactly ten elements, even though more or fewer
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than ten parenthesized substrings may actually have matched.
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This has no effect on <function>ereg</function>'s ability to
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match more substrings. If no matches are found, $regs will not be
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altered by <function>ereg</function>.
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</simpara>
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<simpara>
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Searching is case sensitive.
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</simpara>
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<simpara>
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Returns true if a match for <parameter>pattern</parameter> was
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found in <parameter>string</parameter>, or false if no matches
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were found or an error occurred.
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</simpara>
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<para>
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The following code snippet takes a date in ISO format
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(YYYY-MM-DD) and prints it in DD.MM.YYYY format:
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<example>
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<title><function>ereg</function> Example</title>
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<programlisting role="php">
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if (ereg ("([0-9]{4})-([0-9]{1,2})-([0-9]{1,2})", $date, $regs)) {
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echo "$regs[3].$regs[2].$regs[1]";
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} else {
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echo "Invalid date format: $date";
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}
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</programlisting>
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</example>
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</para>
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<simpara>
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See also <function>eregi</function>,
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<function>ereg_replace</function>, and
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<function>eregi_replace</function>.
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</simpara>
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</refsect1>
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</refentry>
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<refentry id="function.ereg-replace">
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<refnamediv>
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<refname>ereg_replace</refname>
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<refpurpose>Replace regular expression</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>string <function>ereg_replace</function></funcdef>
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<paramdef>string <parameter>pattern</parameter></paramdef>
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<paramdef>string <parameter>replacement</parameter></paramdef>
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<paramdef>string <parameter>string</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<simpara>
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This function scans <parameter>string</parameter> for matches to
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<parameter>pattern</parameter>, then replaces the matched text
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with <parameter>replacement</parameter>.
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</simpara>
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<simpara>
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The modified string is returned. (Which may mean that the
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original string is returned if there are no matches to be
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replaced.)
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</simpara>
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<simpara>
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If <parameter>pattern</parameter> contains parenthesized
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substrings, <parameter>replacement</parameter> may contain
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substrings of the form
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<literal>\\<replaceable>digit</replaceable></literal>, which will
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be replaced by the text matching the digit'th parenthesized
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substring; <literal>\\0</literal> will produce the entire
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contents of string. Up to nine substrings may be used.
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Parentheses may be nested, in which case they are counted by the
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opening parenthesis.
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</simpara>
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<simpara>
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If no matches are found in <parameter>string</parameter>, then
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<parameter>string</parameter> will be returned unchanged.
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</simpara>
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<para>
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For example, the following code snippet prints "This was a test"
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three times:
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<example>
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<title><function>ereg_replace</function> Example</title>
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<programlisting>
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$string = "This is a test";
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echo ereg_replace (" is", " was", $string);
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echo ereg_replace ("( )is", "\\1was", $string);
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echo ereg_replace ("(( )is)", "\\2was", $string);
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</programlisting>
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</example>
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</para>
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<para>
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One thing to take note of is that if you use an integer value as
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the <parameter>replacement</parameter> parameter, you may not get
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the results you expect. This is because
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<function>ereg_replace</function> will interpret the number as
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the ordinal value of a character, and apply that. For instance:
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<example>
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<title><function>ereg_replace</function> Example</title>
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<programlisting>
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<?php
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/* This will not work as expected. */
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$num = 4;
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$string = "This string has four words.";
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$string = ereg_replace('four', $num, $string);
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echo $string; /* Output: 'This string has words.' */
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/* This will work. */
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$num = '4';
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$string = "This string has four words.";
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$string = ereg_replace('four', $num, $string);
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echo $string; /* Output: 'This string has 4 words.' */
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?>
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</programlisting>
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</example>
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</para>
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<simpara>
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See also <function>ereg</function>, <function>eregi</function>,
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and <function>eregi_replace</function>.
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</simpara>
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</refsect1>
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</refentry>
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<refentry id="function.eregi">
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<refnamediv>
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<refname>eregi</refname>
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<refpurpose>case insensitive regular expression match</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>eregi</function></funcdef>
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<paramdef>string <parameter>pattern</parameter></paramdef>
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<paramdef>string <parameter>string</parameter></paramdef>
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<paramdef>array
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<parameter><optional>regs</optional></parameter>
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</paramdef>
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</funcprototype>
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</funcsynopsis>
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<para>
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This function is identical to <function>ereg</function> except
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that this ignores case distinction when matching alphabetic
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characters.
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</para>
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<para>
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See also <function>ereg</function>,
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<function>ereg_replace</function>, and
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<function>eregi_replace</function>.
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</para>
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</refsect1>
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</refentry>
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<refentry id="function.eregi-replace">
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<refnamediv>
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<refname>eregi_replace</refname>
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<refpurpose>replace regular expression case insensitive</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>string <function>eregi_replace</function></funcdef>
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<paramdef>string <parameter>pattern</parameter></paramdef>
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<paramdef>string <parameter>replacement</parameter></paramdef>
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<paramdef>string <parameter>string</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<para>
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This function is identical to <function>ereg_replace</function>
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except that this ignores case distinction when matching
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alphabetic characters.
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</para>
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<para>
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See also <function>ereg</function>, <function>eregi</function>,
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and <function>ereg_replace</function>.
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</para>
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</refsect1>
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</refentry>
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<refentry id="function.split">
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<refnamediv>
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<refname>split</refname>
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<refpurpose>split string into array by regular expression</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>array <function>split</function></funcdef>
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<paramdef>string <parameter>pattern</parameter></paramdef>
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<paramdef>string <parameter>string</parameter></paramdef>
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<paramdef>int
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<parameter><optional>limit</optional></parameter>
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</paramdef>
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</funcprototype>
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</funcsynopsis>
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<para>
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Returns an array of strings, each of which is a substring of
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<parameter>string</parameter> formed by splitting it on
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boundaries formed by the regular expression
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<parameter>pattern</parameter>. If <parameter>limit</parameter>
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is set, the returned array will contain a maximum of
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<parameter>limit</parameter> elements with the last element
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containing the whole rest of <parameter>string</parameter>. If
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an error occurs, <function>split</function> returns false.
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</para>
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<para>
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To split off the first four fields from a line from
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<filename>/etc/passwd</filename>:
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<example>
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<title><function>Split</function> Example</title>
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<programlisting role="php">
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$passwd_list = split (":", $passwd_line, 5);
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</programlisting>
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</example>
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</para>
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<para>
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To parse a date which may be delimited with slashes, dots, or
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hyphens:
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<example>
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<title><function>Split</function> Example</title>
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<programlisting role="php">
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$date = "04/30/1973"; // Delimiters may be slash, dot, or hyphen
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list ($month, $day, $year) = split ('[/.-]', $date);
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echo "Month: $month; Day: $day; Year: $year<br>\n";
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</programlisting>
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</example>
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</para>
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<para>
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Note that <parameter>pattern</parameter> is case-sensitive.
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</para>
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<para>
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Note that if you don't require the power of regular expressions,
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it is faster to use <function>explode</function>, which doesn't
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incur the overhead of the regular expression engine.
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</para>
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<para>
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For users looking for a way to emulate perl's <command>$chars =
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split('', $str)</command> behaviour, please see the examples for
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<function>preg_split</function>.
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</para>
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<para>
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Please note that <parameter>pattern</parameter> is a regular
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expression. If you want to split on any of the characters which
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are considered special by regular expressions, you'll need to
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escape them first. If you think <function>split</function> (or
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any other regex function, for that matter) is doing something
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weird, please read the file <filename>regex.7</filename>,
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included in the <filename>regex/</filename> subdirectory of the
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PHP distribution. It's in manpage format, so you'll want to do
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something along the lines of <command>man
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/usr/local/src/regex/regex.7</command> in order to read it.
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</para>
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<para>
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See also: <function>spliti</function>,
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<function>explode</function>, and <function>implode</function>.
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</para>
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</refsect1>
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</refentry>
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<refentry id="function.spliti">
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<refnamediv>
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<refname>spliti</refname>
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<refpurpose>
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Split string into array by regular expression case insensitive
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</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>array <function>spliti</function></funcdef>
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<paramdef>string <parameter>pattern</parameter></paramdef>
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<paramdef>string <parameter>string</parameter></paramdef>
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<paramdef>int
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<parameter><optional>limit</optional></parameter>
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</paramdef>
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</funcprototype>
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</funcsynopsis>
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<para>
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This function is identical to <function>split</function> except
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that this ignores case distinction when matching alphabetic
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characters.
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</para>
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<para>
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See also : <function>split</function>,
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<function>explode</function> and
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<function>implode</function>.
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</para>
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</refsect1>
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</refentry>
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<refentry id="function.sql-regcase">
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<refnamediv>
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<refname>sql_regcase</refname>
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<refpurpose>
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Make regular expression for case insensitive match
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</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>string <function>sql_regcase</function></funcdef>
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<paramdef>string <parameter>string</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<para>
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Returns a valid regular expression which will match
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<parameter>string</parameter>, ignoring case. This expression is
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<parameter>string</parameter> with each character converted to a
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bracket expression; this bracket expression contains that
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character's uppercase and lowercase form if applicable, otherwise
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it contains the original character twice.
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<example>
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<title><function>Sql_regcase</function> Example</title>
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<programlisting role="php">
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echo sql_regcase ("Foo bar");
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</programlisting>
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</example>
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prints <screen>[Ff][Oo][Oo] [Bb][Aa][Rr]</screen>.
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</para>
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<para>
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This can be used to achieve case insensitive pattern matching in
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products which support only case sensitive regular expressions.
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</para>
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</refsect1>
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</refentry>
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</reference>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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-->
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