preg_quote

php at richardneill dot org (2013-03-25 22:40:34)

preg_quote() only works on the search string, not the replacement string.
But the replacement string isn't always literal, as it can contain backreferences.
There's no function to quote the replacement string, but a workaround is to escape all $ and \ signs:
$replace = str_replace (array('\\','$'),array('\\\\','\$'),$replace);
For example:
$text = 'Test: *#5*';
$search = "*#5*";
$replace = "*$5\\1*";
$search = preg_quote($search, "/");
$replace = str_replace (array('\\','$'),array('\\\\','\$'),$replace);
$new = preg_replace("/$search/", "$replace", $text);
echo "Input: $text\nOutput: $new\n";
Prints:
Input: Test: *#5*
Output: Test: *$5\1*

billadoid at gmail dot com (2012-01-12 05:11:02)

If you need to quote everything but a wildcard, maybe this function will come handy to you:

<?php
protected function _ruleOptionIsMatched($option, $subject)
{
    $option = preg_quote($option, '#');
    $option = str_replace('\*', '.*', $option);

    if(preg_match("#^$option$#", $subject))
    {
        return true;
    }
    else
    {
        return false;
    }
}
?>

admin at nilamo dot com (2010-08-04 08:21:08)

@zooly:
And what if $myvar = 'te\\E.t'? It will match, when it shouldn't. That's why you should use preg_quote().

zooly (2009-07-21 01:07:11)

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

alexc223 at NOSPAM dot googlemail dot com (2009-06-15 00:41:07)

Not sure why this note got deleted, but hey lets try again:
As of PHP 5.3, bug #47229 has been fixed and preg_quote *will* escape a hyphen (-). This may effect your code so ensure this is one thing you check when moving to 5.3.

frostschutz (2009-03-20 02:01:13)

I wanted to escape a string of characters so I could match them in [], i.e. [.,-!"§$%\\\[\]\^].
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 [].

krishoog at gmail dot com (2008-10-13 07:51:57)

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.

bizzigul at hotmail dot fr (2008-07-30 09:10:07)

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...

Anonymous (2007-12-26 15:13:11)

Wondering why your preg_replace fails, even if you have used preg_quote?
Try adding the delimiter / - preg_quote($string, '/');