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Perl: the Markov chain saw

Re: Re: Re: Re: New regex trick...

by japhy (Canon)
on Jul 22, 2002 at 20:49 UTC ( #184233=note: print w/replies, xml ) Need Help??

in reply to Re: Re: Re: New regex trick...
in thread New regex trick...

Oh, \K doesn't stop .* from matching the entire string. Perl is smart enough to back off to the last "." when the \. node comes up.

What \K is doing is faking WHERE in the string (and the pattern) the regex started to match. Compare:

$str = "Match 9 the 1 last 6 digit 2 blah"; $str =~ /.*\d/; print "[$`] [$&] [$']\n"; $str =~ /.*\K\d/; print "[$`] [$&] [$']\n"; __END__ [] [Match 9 the 1 last 6 digit 2] [ blah] [Match 9 the 1 last 6 digit ] [2] [ blah]
See, \K tells $& that THIS is where it begins. This is useful in substitutions:
# you go from this: s/(saveme)deleteme/$1/; # to this: s/saveme\Kdeleteme//;
And you save time on replacing "saveme" with itself.

Jeff[japhy]Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area)
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

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Re: Re: Re: Re: Re: New regex trick...
by redsquirrel (Hermit) on Jul 22, 2002 at 21:08 UTC
    Ah, excellent explanation. That clears things up nicely. ++ to erikharrison for asking the dumb questions that I needed answered.

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