#43532 [Opn]: preg_replace: Escaping \ and $n in 2nd arg

ID: 43532 Updated by: felipe@php.net Reported By: csaba at alum dot mit dot edu Status: Open Bug Type: Documentation problem PHP Version: Irrelevant New Comment: The documentation says: "Note: Single and double quoted PHP strings have special meaning of backslash. Thus if \ has to be matched with a regular expression \\, then "\\\\" or '\\\\' must be used in PHP code." (Maybe the escape will be changed in this post) Its mentioned in: http://br2.php.net/manual/en/reference.pcre.pattern.syntax.php Previous Comments: ------------------------------------------------------------------------ [2007-12-08 02:03:51] csaba at alum dot mit dot edu Description: ------------ preg_replace("/x/", '\\\\', "axb") => a\b This has been reported at least 5 times as a bug in PHP (bugs 11594, 12668, 17616, 34560, 10626), and each time the answer comes back that it's not a bug in PHP, and to check the documentation. There is nothing in the documentation to indicate this behaviour, especially with no /e modifier, so the documentation should be revised. I would suggest something like the below - edit to suit: Csaba Gabor from Vienna $replacement has two type of escaping: pairs of backslashes are combined, and $n is a back reference to a captured (sub)pattern. Example: To make a pure substitution without escaping effects, the following may be used: $subject = "xay"; $replacement = 'b\c\\d\\\e\\\\$0f\\\\\g'; // first one protects backslashes, 2nd one protects $ $aMap = array("/\\\\+/" => '$0$0', "/\\$/" => '\\\\$'); $rep = preg_replace(array_keys($aMap), array_values($aMap),$replacement); // protected replacement $result = preg_replace("/(a)/", $rep, $subject); // original, unprotected replacement $res0 = preg_replace("/(a)/", $replacement, $subject); $replacment => b\c\d\\e\\$0f\\\g $rep => b\\c\\d\\\\e\\\\\$0f\\\\\\g $result => xb\c\d\\e\\$0f\\\gy $res0 => xb\c\d\e\af\\gy ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=43532&edit=1