open A, '1.dat' or die $!;
open B, '2.dat' or die $!;
while (my $lineA=<A>){
    while(my $lineB=<B>){
	print $lineA,' ', $lineB;
    }
}


##</code><code>##

1.dat
----
1
2
3

2.dat
----
a
b
c