You can also use a repeat specifier:

GetOptions ( 
                    "prueba2=s{1,}" => \@array,
 ) or die "not working: $!\n";
[download]

s{1,} means at least one. So you just need to type -p 1 2 3 instead of -p 1 -p 2 -p 3 - if like to save some energy ;-)

Regards, Karl