Check that the parameter is a whole number, meaning there is only digit in it, regex can quickly do that, you basically only want to accept digit from 1 to 9, included:
Code:
if (!$regex($2,^[1-9]$)) {
    msg $chan /me $nick to use the !top command you must specify a positive integer.
  }
Without regex, you could check that with $istok:
Code:
if (!$istok(1 2 3 4 5 6 7 8 9,$2,32)) {

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