print "Index: $_ => \@a: $a[$_], \@b: $b[$_]\n" 
    for grep { $a[$_] != $b[$_] } 0 .. $#a;

##</code><code>##

foreach( 0 .. $#a ) {
    print "Index: $_ => \@a: $a[$_], \@b: $b[$_]\n" if $a[$_] != $b[$_];
}