A module is a package defined in a file whose name is the
same as the package.
Perl locates modules by searching the
@INC array, which contains a list of library directories.
Perl's use of
@INC is roughly comparable to the Unix shell's
use of the PATH environment variable to locate executable programs.
@INC is defined when Perl is built, and can be supplemented
with the -I command-line option to Perl or with
within a program.
When you refer to
ModuleName in your program, Perl
in the directories listed in
@INC for the module file
ModuleName.pm, and uses the first
one it finds. When you
refer to a module embedded in another package, such as
ParentPackage::ModuleName, Perl looks for a
ParentPackage/ subdirectory in the
path, and for a ModuleName.pm file in that subdirectory.
Every Perl installation includes a central lib directory. The actual pathname of this directory varies from system to system, but it's commonly /usr/lib/perl or /usr/local/lib/perl. Looking at the central lib directory for your Perl distribution, you'll see something like this:
When you request the% ls -aF /usr/local/lib/perl ./ I18N/ bigfloat.pl less.pm ../ IO/ bigint.pl lib.pm AnyDBM_File.pm IPC/ bigrat.pl locale.pm AutoLoader.pm Math/ blib.pm look.pl AutoSplit.pm Net/ cacheout.pl man/ Benchmark.pm Pod/ chat2.pl newgetopt.pl Bundle/ Search/ complete.pl open2.pl CGI/ SelectSaver.pm constant.pm open3.pl CGI.pm SelfLoader.pm ctime.pl perl5db.pl CPAN/ Shell.pm diagnostics.pm pod/ CPAN.pm Symbol.pm dotsh.pl pwd.pl Carp.pm Sys/ dumpvar.pl shellwords.pl ...
AnyDBM_Filemodule, it uses AnyDBM_File.pm. When you request the
Math::Complexmodule, it looks for Math/Complex.pm.
usecan also take a list of strings naming entities that you want to import from the module. The list only has to include entities that are not automatically exported by the module. You don't have to provide this list at all if the module automatically exports all the entities you need.
The difference betweenuse Module qw(const1 const2 func1 func2 func3);
usepulls in the module at compile time. This means that functions like
func2can be used as predeclared list operators throughout the file. The
requirecall does not necessarily load the module during compilation, so you must explicitly qualify its routines with the package name.