Wondering why your preg_replace fails, even if you have used preg_quote?
Try adding the delimiter / - preg_quote($string, '/');
(PHP 4, PHP 5, PHP 7)
preg_quote — Quote regular expression characters
$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: . \ + * ? [ ^ ] $ ( ) { } = ! < > | : -
strThe 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.
Returns the quoted (escaped) string.
| Version | Description |
|---|---|
| 5.3.0 | The - character is now quoted |
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>",
$textbody);
?>
Note: This function is binary-safe.
Wondering why your preg_replace fails, even if you have used preg_quote?
Try adding the delimiter / - preg_quote($string, '/');
Note that slash '/' is not one of the special characters, the italic writing of the list above makes pipe '|' look like '/'.
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.
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
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", "", $str)
Apparently using a special char as a delimiter of a regular expression disables this character, i.e. even if it's escaped it's not understood as special character for the expression anymore.
so the pattern "-[a\\-z]-u" matches the characters a, - and z, and not abc...xyz.
It would be nice if preg_quote also escaped characters that have special meanings even if they have this meaning only under certain conditions, such as inside [].
To prevent any problems, try to always use a delimiter that will *almost* not be used inside the regex, such as ` (back quote)
for example: instead of
<?php preg_match('/foo\/bar\//',$somevar); ?>
use
<?php preg_match('`foo/bar/`',$somevar); ?>
it's that simple! like this, you won't have to bother with delimiters anymore...