It is most likely residing at /usr/bin/perl.
Give that a try.
The commands to type given by psyxakias assume that you have shell access to your server. If you are on a shared hosting account, this is probably not the case.
Anyway, DirectAdmin usually uses the /usr/bin/perl path.
In your DirectAdmin control panel there is a link called "Show Installed Perl Modules". It does not give you the path, but if Perl is intalled there will be a bunch of modules shown.
If you are not running your own server, then I recommend contacting your hosting company if your path to Perl is nonstandard.
Good luck.