1
2
3
4

my @a = ( 1, 2, 3, 4, 5, 6, 7, 8 );
my @b = ( 12, 13, 1, 2, 3, 4, 22 );
my %h = map { $_ => 1 } @a;
@b = grep { ! exists $h{$_} } @b;

Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it? -- Brian Kernighan: "The Elements of Programming Style"