Perl, regex greediness problem (possible bug?)

regex greediness problem (possible bug?)

Author	Message
Igor Pechtchans #1 / 2	regex greediness problem (possible bug?) Summary: I'm trying to match a regular expression containing non-printable characters (e.g. "\xFF" or "\x00"). The pattern contains a greediness modifier (".?"), but doesn't work if a non-printable character follows the modifier. If I use a printable character after the "?", the pattern suddenly works... Has anyone else encountered this problem, and, if so, does anyone have a solution? Detail: I'm using perl v. 5.6.1 on cygwin-nt. I'm trying to match various image file headers (GIF, JPEG, PNG, etc) and extract the width and height of the images. I use the following style of regex pattern: $jpghdr = qr/^\xFF\xD8\xFF\xE0..JFIF\x00.?\xFF\xC0...(..)(..)/s; When I include the '?' to modify greediness, the pattern stops working. If I don't include the '?', the pattern works, but, obviously, incorrectly, matching the longest possible string. Aside from the fact that using regular expressions to process chunk-based files is odd, the problem remains that the greediness modifier stops working if followed by a non-printable character. Quoting and the like (\Q..\E, etc) didn't help. ActiveState's perl (v 5.6.0) seems to exhibit the same behavior. Ideas, anyone? Igor
Sun, 16 May 2004 03:39:11 GMT

Jeff 'japhy' Pinya #2 / 2	regex greediness problem (possible bug?) [posted & mailed] On Nov 27, Igor Pechtchanski said: Quote: >Summary: I'm trying to match a regular expression containing >non-printable characters (e.g. "\xFF" or "\x00"). The pattern >contains a greediness modifier (".?"), but doesn't work if a >non-printable character follows the modifier. If I use a printable >character after the "?", the pattern suddenly works... Has anyone >else encountered this problem, and, if so, does anyone have a >solution? This bug was fixed in September (by me :) ). The problem is that there's a line in the regex source that doesn't allow for a high-bit character there. This was fix 12031, which has yet to make it out to a released version of Perl. -- RPI Acacia brother #734 http://www.perlmonks.org/ http://www.cpan.org/ * Look for "Regular Expressions in Perl" published by Manning, in 2002 **
Sun, 16 May 2004 04:53:35 GMT

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