#!usr/bin/perl -w
use strict;

my $string1 = "abcdf";
my $string2 = "abcde";

#for this simple comparision, I assume that using
#the longest string as the iterator value
#which will be "string1", is "better".

if ( length($string2) > length ($string1) )
{
   ($string1,$string2) = ($string2,$string1);
   #in Perl an intermediate "temp" is not necessary
}

my @string2 = split (//,$string2); #array of characters
my $result="";
foreach (split (//,$string1)) #loop var is $_ over chars in
                              #string1
{
   my $char = shift (@string2);
   if (defined ($char) && $char eq $_ )
   {
      $result .= "1";
   }
   else
   {
      $result .= $_;
   }
}
print "CharbyCharResult =$result\n";
print "difference is:",grep{!/1/}split(//,$result),"\n";

__END__
EXAMPLE RUNS:

my $string1 =    "abcdf";
my $string2 =    "abcde";
CharbyCharResult =1111f
difference is:f

my $string1 =    "abcdfccc";
my $string2 =    "abcde";
CharbyCharResult =1111fccc
difference is:fccc

my $string1 =    "abcdf";
my $string2 =    "abcdeeeee";
CharbyCharResult =1111eeeee
difference is:eeeee

my $string1 =    "abcdfxy";
my $string2 =    "abcdexzy";
CharbyCharResult =1111e1zy
difference is:ezy