PHP 5.4.31 Released

preg_quote

(PHP 4, PHP 5)

preg_quoteQuote regular expression characters

Description

string preg_quote ( string $str [, string $delimiter = NULL ] )

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 (escaped) string.

Changelog

Version Description
5.3.0 The - character is now quoted

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.

See Also

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User Contributed Notes 5 notes

up
11
Anonymous
6 years ago
Wondering why your preg_replace fails, even if you have used preg_quote?

Try adding the delimiter / - preg_quote($string, '/');
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7
krishoog at gmail dot com
5 years ago
To bizzigul at hotmail dot fr:
It's not a good practice to make somthing work *almost* all of the time. If the input contains a '`' you will still get an error. I recommend using the default delimiter ('/') and also feed this to preg_quote as second argument.
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3
frostschutz
5 years ago
I wanted to escape a string of characters so I could match them in [], i.e. [.,-!"ยง$%\\\[\]\^].

Unfortunately preg_quote does not escape the - character which has a special meaning in [], i.e. [a-z].

So I used this hack: make - the delimiter of the expression, i.e.

preg_quote(userinput, "-")
preg_replace("-[$userinput]-u", "", $str)

Apparently using a special char as a delimiter of a regular expression disables this character, i.e. even if it's escaped it's not understood as special character for the expression anymore.

so the pattern "-[a\\-z]-u" matches the characters a, - and z, and not abc...xyz.

It would be nice if preg_quote also escaped characters that have special meanings even if they have this meaning only under certain conditions, such as inside [].
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3
zooly
5 years ago
To escape characters with special meaning, like: .-[]() and so on, use \Q and \E.

For example:

<?php echo ( preg_match('/^'.( $myvar = 'te.t' ).'$/i', 'test') ? 'match' : 'nomatch' ); ?>

Will result in: match

But:

<?php echo ( preg_match('/^\Q'.( $myvar = 'te.t' ).'\E$/i', 'test') ? 'match' : 'nomatch' ); ?>

Will result in: nomatch
up
2
bizzigul at hotmail dot fr
5 years ago
To prevent any problems, try to always use a delimiter that will *almost* not be used inside the regex, such as ` (back quote)

for example: instead of
<?php preg_match('/foo\/bar\//',$somevar); ?>

use

<?php preg_match('`foo/bar/`',$somevar); ?>

it's that simple! like this, you won't have to bother with delimiters anymore...
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