Regex Greed

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

I want to find all regex matches within a string. The problem is that sometimes parts of one match are parts of another and I think this is throwing things off.

Example:

$test = "xTx\nxxTxxT";
$rx = 'x...T';
@matches = $test =~ /$rx/sg;
printf "match #%i:\n%s\n",++$i,$_ for @matches;
[download]

The code above finds only 1 match when there are actually 2 matches within the string. Perl grabs the first match "x\nxxT" and then I think it starts looking for a new match where that last one ended. What I'd like to do is also get the other match - "xTxxT".

Is there any way to get Perl to check the entire string for each greedy regex pass excluding any previously found patterns?

Comment on Regex Greed Download Code

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Re: Regex Greed by jwkrahn (Abbot) on Aug 07, 2012 at 21:12 UTC
`$ perl -e' my $test = "xTx\nxxTxxT"; my $rx = qr/(?=(x...T))/s; my @matches = $test =~ /$rx/g; print "match #", $_ + 1, ":\n$matches[$_]\n" for 0 .. $#matches; ' match #1: x xxT match #2: xTxxT` [download]	[reply] [d/l]
Re^2: Regex Greed by kennethk (Abbot) on Aug 07, 2012 at 21:41 UTC
To add a little detail, jwkrahn is using a look ahead so the actual match itself is zero-width. See Looking ahead and looking behind in perlretut. #11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.	[reply]
Re^3: Regex Greed by AnomalousMonk (Archbishop) on Aug 07, 2012 at 22:55 UTC
Unfortunately, the referenced section does not discuss the zero-width-lookahead-to-a-capture trick of jwkrahn's solution. Does anyone know where this is covered in the standard docs (as opposed to a PerlMonks node)?	[reply]
Re^4: Regex Greed by Athanasius (Cardinal) on Aug 08, 2012 at 02:42 UTC
Re^4: Regex Greed by ig (Vicar) on Aug 08, 2012 at 03:16 UTC
Re: Regex Greed by temporal (Pilgrim) on Aug 07, 2012 at 21:45 UTC
Thanks guys, exactly what I was looking for. Always wondered when I'd have to come back and read the regex docs more closely. ^{Strange things are afoot at the Circle-K.}	[reply]
Re^2: Regex Greed by locked_user sundialsvc4 (Abbot) on Aug 08, 2012 at 03:15 UTC
Keep re-reading them. You will always learn something new, and you will never be disappointed or feel that you have wasted your time.
Re^3: Regex Greed by AnomalousMonk (Archbishop) on Aug 08, 2012 at 09:38 UTC
Keep re-reading them. Yea and amen to that, brother! And very often the 'new' thing you learn will be something you forgot five minutes after the last time you read it.	[reply]