This variable returns the number of array elements in @_

<pedant>
Not exactly. $#_ contains the index of the last element in @_. This is actually one less than the number of elements in @_ (assuming that you haven't messed with the value of $[ - which you should never do[1]).
</pedant>

[1] In fact, please forget[2] I ever mentioned that you can.
[2] Please look into the red light *FLASH*

--
<http://www.dave.org.uk>

"The first rule of Perl club is you don't talk about Perl club."