You need to make your own custom sorting routine. Try something along the lines of:

# Note that $a and $b are special globals. DO NOT my THEM!!!
sub my_sort
{
    my ($a_word, $a_num) = $a =~ /^(\w+)(\d+)$/;
    my ($b_word, $b_num) = $b =~ /^(\w+)(\d+)$/;

    return $a_word cmp $b_word || $a_num <=> $b_num;
}

foreach my $file (sort my_sort keys %hash)
{
    print $key, $/;
}
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