sort file1 file2 | uniq -u

##</code><code>##

local *IN;
my %diffs;

open(IN, "sort file1 file2 | uniq -u |") or die 
  "Failed to open pipe to sort/uniq command: $!\n";
++$diffs{$_} while (<IN>);
close(IN) or die "Failed to close pipe: $!\n";
open(IN, "<file1") or die "Failed to open file1: $!\n";
print "In file1 only:\n";
while (<IN>)
{
    if ($diffs{$_})
    {
        print $_;
        delete $diffs{$_};
    }
}

print "\nIn file2 only:\n", keys %diffs, "\n";