#!/usr/bin/perl -w
use strict;
my ($a, $b) = @ARGV;
undef $/;
open(A, $a) or die "cannot open $a: $!";
open(B, $b) or die "cannot open $b: $!";
my $ac = <A>;
my $bc = <B>;
my $al = length $ac;
if ($al != length $bc) {
    print "$a and $b have different lengths\n";
}
elsif ($al) {
    my $errs = 0;
    my $num_okay = 0;
    my $min_num_okay;
    for (my $i = 0; $i < $al; $i++) {
	if (substr($ac, $i, 1) ne substr($bc, $i, 1)) {
	    ++$errs;
	    $min_num_okay = $num_okay;
	    $num_okay = 0;
	}
	else {
	    ++$num_okay;
	}
    }
    print "$a and $b have $errs differences (", $errs / $al, ")\n";
    if (defined $min_num_okay) {
	print "with at least $min_num_okay correct chars between each\n";
    }
}
else {
    print "$a and $b are empty\n";
}