#!/usr/bin/perl -wl

    use strict;

    my %h1;
    my %h2;

    @h1{1..10} = undef;
    print join " ", keys %h1;

    @h1{5..10, 1..4} = undef;
    print join " ", keys %h1;

    @h2{5..10, 1..4} = undef;
    print join " ", keys %h2;

    __END__

    Prints:

    1 2 3 10 4 5 6 7 8 9
    1 2 3 10 4 5 6 7 8 9
    1 2 3 4 10 5 6 7 8 9