foo.pl

use strict;

my @a = (1,2,3,4,5,6,7,8,9);
my @b = (5,2,9,3);

my @x = grep {
    my $_1 = $_;
    my $r = grep {$_ eq $_1} @b;
    $r == 0;
} @a;

printf "%s\n", join(',', @x);