in reply to Mistakenly Believing split is using @_
From perldoc perlfunc:
In scalar context, returns the number of fields found and splits into the "@_" array. Use of split in scalar context is deprecated, however, because it clobbers your subroutine arguments.
It's preventing you from possibly shooting yourself in the foot.
For a better method, use the function length() to count the number of characters in a string.