I also appreciated this solution but for a different reason...it made me look up the $- and $+ variables. Very cool. I think it would be well worth the time for me (and any beginner) to give perldoc perlvar a thorough read...
Cheers everyone, Nathanael >===== Original Message From "Kipp, James" <[EMAIL PROTECTED]> ===== >Thanks. I took a look at your site and book and found the chapter on look >ahead. realized how much i was underutilizing them and they could have saved >me alot of headaches. !! > >> -----Original Message----- >> From: Jeff 'japhy' Pinyan [mailto:[EMAIL PROTECTED]] >> Sent: Friday, October 04, 2002 11:20 AM >> To: Kipp, James >> Cc: [EMAIL PROTECTED] >> Subject: RE: Reg Exp >> >> >> >> $dna =~ m{ >> >> (?= >> >> tag >> >> (?: >> >> .*? tag >> >> # the substr(...) is there to avoid using $& >> >> (?{ push @matches, substr($dna, $-[0], $+[0] - $-[0]) }) >> >> )+ >> >> ) >> >> (?!) >> >> }x; >> >> First of all, I haven't benchmarked, and I had thought of doing the >> index() and substr() as approach that J. Krahn demonstrated. >> >> The regex uses (?= ... ) to look ahead, so it can match stuff without >> consuming it. Here's an example of what I mean: if I have a string >> "ABCADEFA", and I want all chunks of "A...A", if the regex actually >> CONSUMES the "ABCADEFA", then it will have to start after the last A, >> meaning I've missed embedded "ADEFA" chunk. By using a >> look-ahead, I can >> match text while staying where I am in the string. Compare: >> >> print "japhy" =~ /(..)/g; >> >> with >> >> print "japhy" =~ /(?=(..))/g; >> >> Next, to get all the "tag...tag" chunks of varying lengths, I use >> >> /tag(?:.*?tag)+/ >> >> which matches "tagAtag", "tagAtagBtag", "tagAtagBtagCtag", and so on. >> >> The real magic is the code block (?{ ... }) that does the dirty work. >> First of all, substr($DNA, $-[0], $+[0] - $-[0]) is just a way of >> accessing $& without incurring the penalties associated with >> it. So let's >> just use $& for now. The code (push @matches, $&) is >> executed after every >> point that the regex has matched up to an occurence of "tag", so in >> >> tagTHIStagTHATtagTHOSEtag >> >> it'll happen at: >> >> tagTHIStag X >> tagTHIStagTHATtag X >> tagTHIStagTHATtagTHOSEtag X >> tagTHATtag X >> tagTHATtagTHOSEtag X >> tagTHOSEtag X >> >> those six locations. The last thing in the regex is the >> (?!), which is a >> negative look-ahead for nothing, which ALWAYS fails. This forces the >> regex to backtrack, so I get all the matches. >> >> -- >> Jeff "japhy" Pinyan [EMAIL PROTECTED] >> http://www.pobox.com/~japhy/ >> RPI Acacia brother #734 http://www.perlmonks.org/ >http://www.cpan.org/ >** Look for "Regular Expressions in Perl" published by Manning, in 2002 ** ><stu> what does y/// stand for? <tenderpuss> why, yansliterate of course. >[ I'm looking for programming work. If you like my work, let me know. ] > > > >-- >To unsubscribe, e-mail: [EMAIL PROTECTED] >For additional commands, e-mail: [EMAIL PROTECTED] "Ain't no blood in my body, it's liquid soul in my veins" ~Roots Manuva -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
