I'm only a journeyman commandster, unlike
Yoda VSloathe. However the best way to see where anything like PERL or PHP interpreter is is simple, "which PERL" - the answer will be the path to the executable that will be in charge.
Side note, this is a very handy way to see if you're actually using the interpreter that you think you are. When I got my first Power Mac, I compiled PHP 5.0 on it - at the time, OS-X was distributed with 4.3.4. Nothing worked correctly and all was a mess - until I

, did a which PHP and saw that the instance running was not my compiled instance. "which phpize" also helps.
So in wrapping up, the first line of a PERL script that you want executable should be #!(the full path to the PERL interpreter) ... just the same as it would be #!/usr/local/bin/php or whatever for PHP.
Then, as NBs says you'll want to chmod 755 (at least) to make the file actually executable.