Using a Module

A module is a package of useful subroutines and variables that someone has put together. Modules extend the ability of Perl.

Example 1: The File::Basename Module

The File::Basename module is a standard module that is distributed with Perl. When you load the File::Basename module, you get two new functions, basename and dirname.

basename takes a long UNIX path name and returns the file name at the end. dirname takes a long UNIX path name and returns the directory part.

#!/usr/bin/perl # file: basename.pl use strict; use File::Basename; my $path = '/bush_home/bush1/lstein/C1829.fa'; my $base = basename($path); my $dir = dirname($path); print "The base is $base and the directory is $dir.\n";

The output of this program is:

The base is C1829.fa and the directory is /bush_home/bush1/lstein.

The use function loads up the module named File::Basename and imports the two functions. If you didn't use use, then the program would print an error:

Undefined subroutine &main::basename called at basename.pl line 8.

Example 2: The Env Module

The Env module is a standard module that provides access to the environment variables. When you load it, it imports a set of scalar variables corresponding to your environment.

#!/usr/bin/perl # file env.pl use strict; use Env; print "My home is $HOME\n"; print "My path is $PATH\n"; print "My username is $USER\n";

When this runs, the output is:

My home is /bush_home/bush1/lstein
My path is /net/bin:/usr/bin:/bin:/usr/local/bin:/usr/X11R6/bin:/bush_home/bush1/lstein/bin:.
My username is lstein

Controlling What Gets Imported

Each module will automatically import a different set of variables and subroutines when you use it. You can control what gets imported by providing use with a list of what to import.

By default the Env module will import all the environment variables. You can make it import only some:

#!/usr/bin/perl # file env2.pl use strict; use Env '$HOME','$PATH'; print "My home is $HOME\n"; print "My path is $PATH\n"; print "My username is $USER\n";

Global symbol "$USER" requires explicit package name at env2.pl line 9.
Execution of env2.pl aborted due to compilation errors.

You can import scalars, hashes, arrays and functions by giving a list of strings containing the variable or function names. This line imports a scalar named $PATH, an array named @PATH, and a function named printenv.

#!/usr/bin/perl use Env '$PATH','@PATH','printenv'; print join "\n",@PATH;

Output:

/net/bin
/usr/bin
/bin
/usr/local/bin
/usr/X11R6/bin
/bush_home/bush1/lstein/bin
.

You will often see the qw() operator used to reduce typing:

use TestModule qw($PATH $HOME @PATH printenv);

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