Re^4: Regex for matching n-fold repititions of arbitrary characters

Hm ... I follow you so far, ikegami ... but why do I get different output in the following two cases:

~$ perl -le 'print $& if "aabbaab" =~ /aa|bb/g'

~$ perl -le 'print join "\n", ( "aabbaab" =~ /aa|bb/g )'
aa
bb
aa

~$ perl -le 'print join "\n", ( "aabbaab" =~ /(.)\1/g )'
a
b
a
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The first two system responses are clear ... but why does the last regex using backreferences return only single characters?

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Re^5: Regex for matching n-fold repititions of arbitrary characters
by ikegami (Patriarch) on Oct 08, 2009 at 21:17 UTC

/pat/g means /(pat)/g if pat contains no captures. In list context, m// returns what it captured (or 1 if there are no captures) on success.

$ perl -wle'print for "aabbaab" =~ /((.)\2+)/sg;'
aa
a
bb
b
aa
a
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$ perl -wle'print $1 while "aabbaab" =~ /((.)\2+)/sg;'
aa
bb
aa
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Note that if "aabbaab" =~ /aa|bb/g is wrong. Red flags should be raised when you see /g in scalar context outside a loop.

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Re^6: Regex for matching n-fold repititions of arbitrary characters

by LanX (Saint) on Oct 08, 2009 at 21:39 UTC

Note that if "aabbaab" =~ /aa|bb/g is wrong. Red flags should be raised when you see /g in scalar context outside a loop.

Not necessarily! It makes sense when parsing with nested ifs! Friedl's book has some nifty examples...

Cheers Rolf

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Re^7: Regex for matching n-fold repititions of arbitrary characters

by ikegami (Patriarch) on Oct 09, 2009 at 02:19 UTC

I didn't say m//g in scalar context outside a loop is wrong. I said it's usually wrong. I said the code he used was wrong.

And I bet his tokenizers used /c too

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Re^5: Regex for matching n-fold repititions of arbitrary characters
by bv (Friar) on Oct 08, 2009 at 20:21 UTC

Because you are only capturing one character. m// in list context returns the list of captures, which in your case is the (.). The backreference is not captured.

print pack("A25",pack("V*",map{1919242272+$_}(34481450,-49737472,6228,0,-285028276,6979,-1380265972)))

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Re^5: Regex for matching n-fold repititions of arbitrary characters
by LanX (Saint) on Oct 08, 2009 at 21:28 UTC

$ perl -e 'print $1,$2,"\n" while ( "aabbaab" =~ /(.)(\1)/g )'
aa
bb
aa
[download]

$ perl -e 'print $&,"\n" while ( "aabbaab" =~ /(.)\1/g )'
aa
bb
aa
[download]

Cheers Rolf

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