foreach $key ((sort keys %user_hash)[0 .. $x]) {
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Should do the thick, but it will build a seperate list of all the keys first that might take a lot of memory, which is not needed, especially if you only want a relatively small number of keys, so:

foreach $key (sort keys %user_hash) {
   last if $key_count++ > $x;
   ...
}
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will work a little more efficient.

Update: Abigail is right, the problem is in the sorting. I don't know what the difference will be when you remove the sort from the first method though the second would certainly not take more elements than nessicary.

-- 
Joost       downtime n. The period during which a system
            is error-free and immune from user input.
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