One way (under almost every operating system -- AmigaOS being a notable (almost) exception) to return allocated memory so that other processes can make use of it is to exit or exec. Etc.

So an alternate solution is to have your memory hog restart itself by execing itself. To do this, you'll probably need to persist some state from the old to the new instance of the script. Sometimes this is as simple as passing some command-line parameters to the new instance. Other times you might have to serialize some data structures to a temporary file to be restored by the new instance. Or you can even start the new instance and serialize your state down a pipe to it before the old instance exits.

Oh, and, just to stress the point, Perl doesn't have a traditional garbage collector. There is nothing to trigger. "Garbage" is "collected" when the number of references to it goes to zero (except for "temporary" garbage which may not be collected until roughly the end of the statement). undef does remove references and so will "collect" "garbage" unless you've made other references to that garbage.

        - tye (but my friends call me "Tye")