Learning Perl, 5th Edition

Some Important Modules

We describe some of the most important features^[*] of the most important modules^[†] in this section. The modules that we discuss here should generally be found on every machine that has Perl, except where noted otherwise. You can always get the latest ones from CPAN.

The CGI Modules

Many people use Perl to write programs that a web server will run, generally called CGI programs. The CGI module comes with Perl. We showed a simple example in Chapter 11, and you can read more later in this appendix.

The Cwd Module

Sometimes you need to know what the current working directory’s name is. (Well, you could often use ., but maybe you need to save the name so that you can change back to this directory later.) The Cwd module—which comes with Perl—provides the cwd function, which you can use to determine the current working directory:

use Cwd;

my $directory = cwd;

The Fatal Module

If you get tired of writing "or die" after every invocation of open or chdir, then maybe the Fatal module is for you. Just tell it which functions to work with, and those will be automatically checked for failure, as if you’d written "or die" and a suitable message after each one. This won’t affect such calls in someone else’s package (that is, code contained within a module you’re using, for example), so don’t use this to fix up poorly written code. It’s just a timesaver, mostly for simple programs in which you don’t need direct control over the error message itself. For example:

use Fatal qw/ open ...