Programming Perl, 4th Edition

use

use MODULE VERSION LIST
use MODULE VERSION ()
use MODULE VERSION
use MODULE LIST
use MODULE ()
use MODULE
use VERSION

The use declaration loads in a module, if it hasn’t been loaded before, and imports subroutines and variables into the current package from the named module. (Technically speaking, it imports some semantics into the current package from the named module, generally by aliasing certain subroutine or variable names into your package.) Most use declarations look like this:

use MODULE LIST;

That is exactly equivalent to saying:

BEGIN { require MODULE; import MODULE LIST }

The BEGIN forces the require and import to happen at compile time. The require makes sure the module is loaded into memory if it hasn’t been yet. The import is not a built-in—it’s just an ordinary class method call into the package named by MODULE to tell that module to pull the list of features back into the current package. The module can implement its import method any way it likes, though most modules just choose to derive their import method via inheritance from the Exporter class that is defined in the Exporter module. See Chapter 11 and the Exporter module for more information. If no import method can be found, then the call is skipped without murmur.

If you don’t want your namespace altered, supply ...