Hey.. anyone know what the following perl command does ?
system("gdg -r 9 -e $last_sys_ref >/dev/null 2>&1");
whats gdg ? with all those options.

Does it try to delete the contents of the file referenced by $last_sys_ref ?

The "system( )" syntax says to run what is inside the parameters as if it were typed at a command line.

Type "which gdg" to find out where gdg command is. Do a "file <pathto>/gdg" to find out what kind of file. If it is ASCII or text (or script) you should be able to view the file and get a clue what it is.
You can try "man -k gdg" to see if there are any man pages for gdg known on your system. If not you might be able to find more information near where the gdg command was found. (That is if for example you found gdg in something like /opt/gdg/bin/gdg then there may be other files in the /opt/gdg directory structure that help you figure out what it is.)

I've never heard of gdg myself.

gdg is going to be something that is called from outside perl as the line is using the 'system' call.
you will have to examine the contents of the file gdg to know what that does