#!/usr/bin/perl -w
use strict;
use Benchmark "cmpthese";

my $match = "abcdefghijklmnopqrst";
my $matchlen = length($match);
my $linelen = 50;
my @lines;
my $i = 0;
for (1..1e3) {
    my $line = join '', map chr(32+rand 96), 1..$linelen;
    my $s = $match;
    substr($s, $i++ % $matchlen, 1) = 'X';
    substr($line, rand $linelen-$matchlen, $matchlen) = $s;
    push @lines, $line;
}
my @patterns = ($match);
for my $i (0..$matchlen-1) {
    my $p = $match;
    substr($p, $i, 1) = ".";
    push @patterns, qr/$p/;
}

sub xorstr {
    my $line = shift;
    for my $i (0..$linelen-$matchlen) {
        my $s = substr $line, $i, $matchlen;
        my $x = $s ^ $match;
        my $diff = $x =~ tr/\0//c;
        return $s unless $diff > 1;
    }
    
}
sub regex {
    my $line = shift;
    for my $p (@patterns) {
        if ( $line =~ m/($p)/ ) {
            return $1;
        }
    }
}

cmpthese(-5,
    {
        regex  => sub { my $r = regex($_)  for @lines },
        xorstr => sub { my $r = xorstr($_) for @lines },
    }
);

__END__
         Rate  regex xorstr
regex  17.3/s     --   -82%
xorstr 97.3/s   462%     --