Programming Perl, 4th Edition

less

use less;

use less "CPU";
use less "memory";
use less "time";
use less "disk";
use less "fat";         # great with "use locale";

Implemented in v5.10 and later, this pragma is intended to someday give hints to the compiler, code-generator, or interpreter to enable certain trade-offs by using the new hints hash reference that caller now returns.

This module has always been part of the Perl distribution (as a joke), but it didn’t do anything until v5.10. Even then, hints are available only in their lexical scope, so although the pragma documentation makes it sound as though another module can easily find out what you want less of, this is still only a demonstration of the new caller feature.

It is not an error to ask to use less of something that Perl doesn’t know how to make less of right now.