PHP preg_quote() Function

The PHP preg_quote() function 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: . \ + * ? [ ^ ] $ ( ) { } = ! < > | : - #

Please note that / is not a special regular expression character.

Syntax

preg_quote(str, delimiter)

Parameters

Return Value

Returns the quoted (escaped) string.

Example: preg_quote() example

The example below shows the usage of preg_quote() function.

<?php
//a string which need to be escaped
$str = 'send $100 to D/303';

//using preg_quote function 
$str = preg_quote($str, '/');

//displaying the result
echo $str;
?>

The output of the above code will be:

send \$100 to D\/303

Example: italicizing a word within given text

In the example below a word containing asterisks is italicized. As asterisk has special meaning in the regular expression. Therefore it is first escaped using preg_quote() function.

<?php
//asterisk has special meaning in the regular 
//expression, therefore it should be escaped first
$str = "This book is *very* difficult to find.";

$word = "*very*";

//italicizing the $word
$str = preg_replace ("/".preg_quote($word, '/')."/",
                     "<i>".$word."</i>", $str);

//displaying the result
echo $str;
?>

The output of the above code will be:

This book is <i>*very*</i> difficult to find.