Hashes with the same keys won't necessarily return the keys in the same order, as shown below. However, as Juerd points out, the order shouldn't change for a given hash if the keys don't change, also shown below.

The only problem that I can see is that the order the keys are returned in might change in a future release. So, I wouldn't rely on that.

    #!/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
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--
John.