Finding characters where two string differs can be done with bitwise operations. If you binary XOR two strings, positions where both characters are the same come out as a null byte. When doing several comparisons, one can accumulate the differing positions using binary OR: 


use warnings;
use strict;
use 5.010; # for say()

my $a='AAATGCCTT';
my $b='AAAAGCGTC';
my $c='AAAGGCGTC';

my $mask = chr(0) x length $a;
for ($b, $c) {
    $mask |= $a ^ $_;
}

# just to illustrate what the mask looks like:
use Data::Dumper;
$Data::Dumper::Useqq = 1;


# count number of 0-bytes
my $matches =()= $mask =~ /\0/g;
say "Matches:     ", $matches;
say "Non-matches: ", length($a) - $matches;

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This approach should scale well for longer strings, since the binary operations are faster than looping over all characters.

Perl 6 - the future is here, just unevenly distributed

In reply to Re: Is it possible to find the number of matching and non-matching positions in strings using perl code? by moritz
in thread Is it possible to find the number of matching and non-matching positions in strings using perl code? by supriyoch_2008

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