You want to compare each element of @a against the element of the same index in @b, right? This will do it.

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

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

Which you choose kind of depends on whether you're more interested in keeping a list of indices to the dissimilar elements, or simply interested in processing the mismatches one by one. The grep version is handy for getting the list of mismatches.