An alternative is to pass references to the arrays to the function:

getlists(\@a, \@b);
print join(" ",@a),"\n",join(" ",@b);

sub getlists {
    my @foo = (1,2,3);
    my @bar = (4,5,6);
    @{$_[0]} = @foo;
    @{$_[1]} = @bar;
}
[download]

or

getlists(\@a, \@b);
print join(" ",@a),"\n",join(" ",@b);

sub getlists {
    my ($foo, $bar) = @_;
    @$foo = (1,2,3);
    @$bar = (4,5,6);
}
[download]