$str = 'PolarBear';
my @str = split//,$str;
my @pats = qw(polarbear Polerbear Polarbeer);
for (@pats) {
    my @mat = mismatches($_,$str);
    print "Mismatches for $_ vs $str: @mat\n";
}

sub mismatches
{
    my ($p1,$p2) = @_;
    my @foo = split//,$p1;
    my @str = split//,$p2;
    my @pos;
    if ($#foo > $#str) {
        for (0 .. $#foo) {
            push @pos, $_ if $foo[$_] ne $str[$_];
        }
    } else {
        for (0 .. $#str) {
            push @pos, $_ if $foo[$_] ne $str[$_];
        }
    }
    return @pos;
}