perl -e '
use strict;

my @a=qw{1 2 3};
my @b=qw{4 5};
my @c=();
foreach my $a (@a) {
  foreach my $b (@b) {
    push @c, [$a, $b];
  }
}
print join("\n", map {join ",", @$_} @c), "\n"
'

---
1,4
1,5
2,4
2,5
3,4
3,5