Now that you've solved the problem with a perl script, you might still want to know that the unix/cygwin "sort" command does this, when you use the appropriate option flags -- e.g.:

sort -n +1  a_file > a_sorted_file
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If you only want the first few lines, try the "head" command:

sort -n +1  a_file | head -5 > first_five_sorted
[download]