PHP Manual: preg

Description

function preg_quote(string $str, ?string $delimiter = null): string

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

Note that / is not a special regular expression character.

Note:
Note that preg_quote() is not meant to be applied to the $replacement string(s) of preg_replace() etc.

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 (escaped) string.

Changelog

Version	Description
7.3.0	The `#` character is now quoted
7.2.0	`delimiter` is nullable now.

Examples

Example #1 preg_quote() example

<?php
$keywords = '$40 for a g3/400';
$keywords = preg_quote($keywords, '/');
echo $keywords; // returns \$40 for a g3\/400
?>

Example #2 Italicizing a word within some text

<?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.