@ARGV = qw(file1 file2);
my %found_in;
while (<>) {
  $found_in{$_} .= $ARGV;
}
print "file1 and not file2:\n";
print grep { $found_in{$_} eq "file1" }, keys %found_in;
print "file2 and not file1:\n";
print grep { $found_in{$_} eq "file2" }, keys %found_in;