Character match count between strings in Perl - regex

Question

I have a string (say string 1) that needs to be matched to another string (string2). Both the strings will have the same length and are case in-sensitive.
I want to print the number of character matches between both the strings.
E.g.: String 1: stranger
String 2: strangem
Match count = 7
I tried this:
$string1 = "stranger";
$string2 = "strangem";
my $count = $string1 =~ m/string2/ig;
print "$count\n";
How can I fix this?

Answer 1

Exclusive or, then count the null characters (where the strings were the same):
my $string1 = "stranger";
my $string2 = "strangem";
my $count = ( lc $string1 ^ lc $string2 ) =~ tr/\0//;
print "$count\n";
I missed the "case in-sensitive" bit.

Answer 2

You can use substr for that:
#!/usr/bin/perl
use warnings;
use strict;
my $string1=lc('stranger');
my $string2=lc('strangem');
my $count=0;
for (0..length($string1)-1) {
$count++ if substr($string1,$_,1) eq substr($string2,$_,1);
}
print $count; #prints 7
Or you can use split to get all characters as an array, and loop:
#!/usr/bin/perl
use warnings;
use strict;
my $string1=lc('stranger');
my $string2=lc('strangem');
my $count=0;
my #chars1=split//,$string1;
my #chars2=split//,$string2;
for (0..$#chars1) {
$count++ if $chars1[$_] eq $chars2[$_];
}
print $count; #prints 7
(fc gives more accurate results than lc, but I went for backwards compatibility.)

Answer 3

Not tested
sub cm
{
my #a = shift;
my #b = shift;
# First match prefix of string:
my $n = 0;
while ($n < $#a && $n < $#b && $a[$n] eq $b[$n]) {
++$n;
}
# Then skip one char on either side, and recurse.
if ($n < $#a && $n < $#b) {
# Match rest by skipping one place:
my $n2best = 0;
my $n2a = cm(splice(#a, $n), splice(#b, $n + 1));
$n2best = $n2a;
my $n2b = cm(splice(#a, $n + 1), splice(#b, $n));
$n2best = $n2b if $n2b > $n2best;
my $n2c = cm(splice(#a, $n + 1), splice(#b, $n + 1));
$n2best = $n2c if $n2c > $n2best;
$n += $n2best;
}
return $n;
}
sub count_matches
{
my $a = shift;
my $b = shift;
my #a_chars = split //, $a;
my #b_chars = split //, $b;
return cm(#a_chars, #b_chars);
}
print count_matches('stranger', 'strangem')