preg_quote

Quote regular expression characters (PHP 4, PHP 5)
string preg_quote ( string str [, string delimiter] )

preg_quote() takes str and puts a backslash in front of every character that is part of the regular expression syntax. This is useful if you have a run-time string that you need to match in some text and the string may contain special regex characters.

The special regular expression characters are: . \ + * ? [ ^ ] $ ( ) { } = ! < > | :

Parameters

str: The input string.
delimiter: If the optional delimiter is specified, it will also be escaped. This is useful for escaping the delimiter that is required by the PCRE functions. The / is the most commonly used delimiter.

Return Values

Returns the quoted string.

Examples

Example 1721. preg_quote() example

copy to clipboard

<?php

$keywords = '$40 for a g3/400';
$keywords = preg_quote($keywords, '/');

echo $keywords; // returns \$40 for a g3\/400
?>

Example 1722. Italicizing a word within some text

copy to clipboard

<?php
// In this example, preg_quote($word) is used to keep the

// asterisks from having special meaning to the regular

// expression.

$textbody = "This book is *very* difficult to find.";
$word = "*very*";
$textbody = preg_replace ("/" . preg_quote($word) . "/",

                          "<i>" . $word . "</i>",

                          $textbody);
?>

Notes

Note:

This function is binary-safe.

Code Examples / Notes » preg_quote

Re: adrian holovaty You must also escape '#' character. Next thing is that there is more then one whitespace character (a space).. Also IMO the name preg_quote_white() won't tell what the new function does so we could rename it. And finally, we should also add $delimiter: <?php function preg_xquote($a, $delimiter = null) { if ($delimiter) { return preg_replace('/[\s#]/', '\\\0', preg_quote($a, substr("$delimiter", 0, 1))); } else { return preg_replace('/[\s#]/', '\\\0', preg_quote($a)); } } ?>

Note that if you've used the "x" pattern modifier in your regex, you'll want to make sure you escape any whitespace in your string that you *want* the pattern to match. A simplistic example: $phrase = 'a test'; // note the space $textbody = 'this is a test'; // Does not match: preg_match('/' . preg_quote($phrase) . '$/x', $textbody); function preg_quote_white($a) { $a = preg_quote($a); $a = str_replace(' ', '\ ', $a); return $a; } // Does match: preg_match('/' . preg_quote_white($phrase) . '$/x', $textbody);

If you are placing your quoted string within []'s, make sure you also escape the dash (-) character manually. preg_match("/^[A-Za-z\d" . preg_quote('!@#$%^&*()-_=+\|[]{};:/?.><', '/') . "]{8,32}$/", $password) The above will try to match the characters ')' through '_' whatever those are. So use the below expression: preg_match("/^[A-Za-z\d" . preg_quote('!@#$%^&*()_=+\|[]{};:/?.><', '/') . "\-]{8,32}$/", $password) Yes, I know I can use \w in place of A-Za-z, but I wanted to illustrate my point better :)