If don't know if your solution does the right thing or not, but I do know it can be optimized. What follows does exactly the same thing as yours, except it does it in O(n) time instead of O(n*n)

my @list1 = qw/a b c d e f g/;
my @list2 = qw/a b c d e /;

my %one = ( a => 1, b => 1, c => 1 );
my %two = ( f => 1, g => 1 );


my %list1;
undef @list1{@list1};

my %list2;
undef @list2{@list2};


foreach my $key (keys %one) {
   if (exists $list1{$key} && exists $list2{$key}) {
      print "File 1 $key", $/;
   }
}

foreach my $key (keys %two) {
   unless (exists $list1{$key} && exists $list2{$key}) { 
      if (exists $list1{$key} || exists $list2{$key}) {
         print "File 2 $key", $/;
      }
   }
}
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