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

[download]

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 },
};

[download]

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)

In reply to Re^2: Regular Expression by nobull
in thread Regular Expression by FarTech

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