#41739 [NEW]: Escaped backslash in PCRE regex documentation

From: trex0003 at umn dot edu Operating system: CentOS PHP version: Irrelevant PHP Bug Type: Documentation problem Bug description: Escaped backslash in PCRE regex documentation Description: ------------ Documentation of how PCRE regex behaves with escaped backslashes is confusing as written in current documentation: http://php.planetmirror.com/manual/en/reference.pcre.pattern.syntax.php Perhaps this just means an expansion of the note: "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." While trying to use preg_split to break a string at non-escaped string quotes, I tried using a negative lookbehind assertion (see code below). With all other escaped characters in the lookbehind assertion, you only need one backwards slash before the escaped character (e.g., "(?<!\s)" works); but if you want to escape a backslash, you need to escape it twice (e.g., "(?<!\\\)" works but "(?<!\\)" does not). Based on the documentation's statement 'In particular, if you want to match a backslash, you write "\\".' it seems that (?<!\\) should work, and the extra information in the Note is too terse to explain why. Perhaps this is actually a bug, but I can't tell if it's normal behavior that could be clarified more in documentation. The closest I could find for bug reports to this issue is here: http://bugs.php.net/bug.php?id=22315 ...but this only implies the difference in behavior without explaining why. Reproduce code: --------------- $string = "This sentence is not quoted. 'But this one is, and it contains \'escaped quotes\' within!'"; $needle = "/(?<!\\)'/"; $results = preg_split($needle, $string); print_r($results); Expected result: ---------------- Array ( [0] => This sentence is not quoted. [1] => But this one is, and it contains \'escaped quotes\' within! [2] => ) // Adding a third backslash to the $needle gives this result. Actual result: -------------- Warning: preg_split() [function.preg-split]: Compilation failed: missing ) at offset 7 in /data/domains/lawweb3.law.umn.edu/public/php/regex.php on line 16 -- Edit bug report at http://bugs.php.net/?id=41739&edit=1 -- Try a CVS snapshot (PHP 4.4): http://bugs.php.net/fix.php?id=41739&r=trysnapshot44 Try a CVS snapshot (PHP 5.2): http://bugs.php.net/fix.php?id=41739&r=trysnapshot52 Try a CVS snapshot (PHP 6.0): http://bugs.php.net/fix.php?id=41739&r=trysnapshot60 Fixed in CVS: http://bugs.php.net/fix.php?id=41739&r=fixedcvs Fixed in release: http://bugs.php.net/fix.php?id=41739&r=alreadyfixed Need backtrace: http://bugs.php.net/fix.php?id=41739&r=needtrace Need Reproduce Script: http://bugs.php.net/fix.php?id=41739&r=needscript Try newer version: http://bugs.php.net/fix.php?id=41739&r=oldversion Not developer issue: http://bugs.php.net/fix.php?id=41739&r=support Expected behavior: http://bugs.php.net/fix.php?id=41739&r=notwrong Not enough info: http://bugs.php.net/fix.php?id=41739&r=notenoughinfo Submitted twice: http://bugs.php.net/fix.php?id=41739&r=submittedtwice register_globals: http://bugs.php.net/fix.php?id=41739&r=globals PHP 3 support discontinued: http://bugs.php.net/fix.php?id=41739&r=php3 Daylight Savings: http://bugs.php.net/fix.php?id=41739&r=dst IIS Stability: http://bugs.php.net/fix.php?id=41739&r=isapi Install GNU Sed: http://bugs.php.net/fix.php?id=41739&r=gnused Floating point limitations: http://bugs.php.net/fix.php?id=41739&r=float No Zend Extensions: http://bugs.php.net/fix.php?id=41739&r=nozend MySQL Configuration Error: http://bugs.php.net/fix.php?id=41739&r=mysqlcfg