Lookahead regex help

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

Hey. I have a string that contains data similiar to this: 'aaabbcdd'. I was trying to write write a regex that would match 'aaa' then 'bb' then 'c' and then 'dd'. That is, it would group together everything that is the same.

I figured I would have to use the lookahead operator to check to see if what he just matched matches what is next but I am not sure how to do this. Also I was planning on doing it in a while loop like this:

my $string = 'aaabbcddeef';

while($string =~ m/\w(?!patternthatworkd)/gi) {
 do stuff....
}
[download]

Thanks for any help

Comment on Lookahead regex help Download Code

Replies are listed 'Best First'.
Re: Lookahead regex help by borisz (Canon) on Aug 16, 2004 at 16:24 UTC
Im not really sure if this is what you have in mind: `my $string = 'aaabbcddeef'; while($string =~ m/((.)\2*)/gi) { print "$1\n"; } __OUTPUT__ aaa bb c dd ee f` [download] Boris	[reply] [d/l]
Re^2: Lookahead regex help by debiandude (Scribe) on Aug 16, 2004 at 16:34 UTC
That seems to work. Thanks. But I am curious as to what the \2 does?	[reply]
Re^3: Lookahead regex help by borisz (Canon) on Aug 16, 2004 at 16:37 UTC
\2 looks for what the second () pair has captured. In this case a single char. Boris	[reply]
Re^3: Lookahead regex help by Anonymous Monk on Aug 17, 2004 at 02:25 UTC
$$ perl -MYAPE::Regex::Explain -e'die YAPE::Regex::Explain->new(qr/((. +)\2)/i)->explain' The regular expression: (?i-msx:((.)\2)) matches as follows: NODE EXPLANATION ---------------------------------------------------------------------- (?i-msx: group, but do not capture (case-insensitive) (with ^ and $ matching normally) (with . not matching \n) (matching whitespace and # normally): ---------------------------------------------------------------------- ( group and capture to \1: ---------------------------------------------------------------------- ( group and capture to \2: ---------------------------------------------------------------------- . any character except \n ---------------------------------------------------------------------- ) end of \2 ---------------------------------------------------------------------- \2* what was matched by capture \2 (0 or more times (matching the most amount possible)) ---------------------------------------------------------------------- ) end of \1 ---------------------------------------------------------------------- ) end of grouping ---------------------------------------------------------------------- [download]	[reply] [d/l]


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