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Re^2: Regular Expression

by nobull (Friar)
on Feb 09, 2005 at 20:14 UTC ( #429495=note: print w/replies, xml ) Need Help??

in reply to Re: Regular Expression
in thread Regular Expression

$string =~ m/(?=.*abc)(?=.*xyz)/i;

That unanchored pattern is pathologically inficient. If the string does not match it will try and fail at every character position. Even with a relatively short strings this has a considerable effect.

use Benchmark; my $string = 'x' x 100; timethese 1_000_000 => { unanchored => sub { $string =~ /(?=.*abc)(?=.*xyz)/i }, anchored => sub { $string =~ /^(?=.*abc)(?=.*xyz)/i }, };

Benchmark: timing 1000000 iterations of anchored, unanchored...
anchored: 1 wallclock secs ( 1.30 usr + 0.00 sys = 1.30 CPU) @ 768049.16/s (n=1000000)
unanchored: 70 wallclock secs (70.12 usr + 0.00 sys = 70.12 CPU) @ 14261.06/s (n=1000000)

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