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

From: csaba at alum dot mit dot edu Operating system: PHP version: Irrelevant PHP Bug Type: Documentation problem Bug description: preg_replace: Escaping \ and $n in 2nd arg 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 bug report at http://bugs.php.net/?id=43532&edit=1 -- Try a CVS snapshot (PHP 4.4): http://bugs.php.net/fix.php?id=43532&r=trysnapshot44 Try a CVS snapshot (PHP 5.2): http://bugs.php.net/fix.php?id=43532&r=trysnapshot52 Try a CVS snapshot (PHP 5.3): http://bugs.php.net/fix.php?id=43532&r=trysnapshot53 Try a CVS snapshot (PHP 6.0): http://bugs.php.net/fix.php?id=43532&r=trysnapshot60 Fixed in CVS: http://bugs.php.net/fix.php?id=43532&r=fixedcvs Fixed in release: http://bugs.php.net/fix.php?id=43532&r=alreadyfixed Need backtrace: http://bugs.php.net/fix.php?id=43532&r=needtrace Need Reproduce Script: http://bugs.php.net/fix.php?id=43532&r=needscript Try newer version: http://bugs.php.net/fix.php?id=43532&r=oldversion Not developer issue: http://bugs.php.net/fix.php?id=43532&r=support Expected behavior: http://bugs.php.net/fix.php?id=43532&r=notwrong Not enough info: http://bugs.php.net/fix.php?id=43532&r=notenoughinfo Submitted twice: http://bugs.php.net/fix.php?id=43532&r=submittedtwice register_globals: http://bugs.php.net/fix.php?id=43532&r=globals PHP 3 support discontinued: http://bugs.php.net/fix.php?id=43532&r=php3 Daylight Savings: http://bugs.php.net/fix.php?id=43532&r=dst IIS Stability: http://bugs.php.net/fix.php?id=43532&r=isapi Install GNU Sed: http://bugs.php.net/fix.php?id=43532&r=gnused Floating point limitations: http://bugs.php.net/fix.php?id=43532&r=float No Zend Extensions: http://bugs.php.net/fix.php?id=43532&r=nozend MySQL Configuration Error: http://bugs.php.net/fix.php?id=43532&r=mysqlcfg