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Re: Re: parsing question

by Chady (Priest)
on May 28, 2003 at 09:30 UTC ( #261261=note: print w/replies, xml ) Need Help??


in reply to Re: parsing question
in thread parsing question

or maybe a greedy regex?

$line =~ s/^(.*>) ;.*/\1;/;

He who asks will be a fool for five minutes, but he who doesn't ask will remain a fool for life.

Chady | http://chady.net/

Replies are listed 'Best First'.
Re: Re: Re: parsing question
by kilinrax (Deacon) on May 28, 2003 at 11:06 UTC

    In a word, no.

    Reversing the regex is much faster.
    Have a look at these benchmarks:

    #!/usr/bin/perl -w use strict; use Benchmark; my $string = "<<HTML>;nbsp dont_strip_me</HTML>> <xyzfdgfghgf> ;strip_ +me"; sub reversed { my $reverse = reverse(shift); $reverse =~ s| \w* ; \s* > |>|x; return scalar reverse $reverse; } sub greedy { my $line = shift; $line =~ s|^ (.*>) \s* ; \w* |$1|x; return $line; } print "Reversed: ", reversed($string), "\n"; print "Greedy: ", greedy($string), "\n"; timethese( -10,{ reversed => sub { reversed( $string ) }, greedy => sub { greedy( $string ) }, } );

    Output:

    Reversed: <<HTML>;nbsp dont_strip_me</HTML>> <xyzfdgfghgf>
    Greedy: <<HTML>;nbsp dont_strip_me</HTML>> <xyzfdgfghgf>
    Benchmark: running greedy, reversed, each for at least 10 CPU seconds...
        greedy: 10 wallclock secs ( 9.98 usr + 0.02 sys = 10.00 CPU) @ 78480.80/s (n=784808)
      reversed: 11 wallclock secs (10.46 usr + 0.00 sys = 10.46 CPU) @ 167660.04/s (n=1753724)

    As you can see, it's over twice the speed. On longer strings, the difference would be even greater.

    Also, your regex is wrong. Read through perldoc:perlre (specifically, the section marked 'Warning on \1 vs $1') to discover why.

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