Regex: continuous matching positions

theshz has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I'd like to find all occurances of a pattern and its start/end matching positions:

# To find all occurance of "bc" preceeded by 3 letters, and followed b
+y 2 letters.
$str = "aaabcabcdebcaabebcb";
while($str =~ /(\w{3}bc\w{2})/g){
    print "$-[1],$+[1],$1\n";
}
__OUTPUT__
0,7,aaabcab
7,14,cdebcaa
[download]

It didn't quite do what I want. I'd like it to match 3 times:

__OUTPUT__
0,6,aaabcab
3,9,bcabcde
7,13,cdebcaa
[download]

Thanks.

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Re: Regex: continuous matching positions by Tanktalus (Canon) on Apr 26, 2006 at 15:45 UTC
Check out the pos function. For example: `$str = "aaabcabcdebcaabebcb"; while($str =~ /(\w{3}bc\w{2})/g){ print "$-[1],$+[1],$1\n"; pos($str) = $-[1]+1; }` [download] This sets the position to start looking for the next match to 1 past the start point of the previous match. And it gets you the output you want.	[reply] [d/l]
Re: Regex: continuous matching positions by japhy (Canon) on Apr 26, 2006 at 16:07 UTC
The problem is that the regex consumes the characters it matches (so the next match happens after those characters). Use a look-aahead to not consume: `while ($str =~ /(?=(\w{3}bc\w{2}))/g) { print "$-[1],$+[1],$1\n"; }` [download] Update: extra ')' added to regex (thanks SamCG and prasadbabu!) Jeff `japhy` Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and `perl` hacker How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart	[reply] [d/l]
Re: Regex: continuous matching positions by duff (Parson) on Apr 26, 2006 at 15:48 UTC
Use zero-width lookahead and lookbehind: `$str = "aaabcabcdebcaabebcb"; while($str =~ /(?<=\w{3})(bc)(?=\w{2})/g){ print "$-[1],$+[1],$1\n"; }` [download] update: As my esteemed fellow monk Tankalus reminds me, you'll need to adjust your mechanism for retrieving the exact characters you require. duff	[reply] [d/l]