If you use a module, Perl deals with it at compile time. If you require a module, Perl deals with it at run time.

I typically like to use a module because it allows me to check everything via a perl -c someprog.pl after I've finished coding. It I used require instead, I wouldn't find out that something was wrong until I ran the program for the first time. YMMV, just my own personal preference.

require is handy though if your program needs to do something based on whether you have a module installed on your system. You can test for this at runtime.

#!/usr/bin/perl -w

use strict;

# do we have FOO::Bar on this system?
eval { require FOO::Bar };
if ($@) {
   # FOO::Bar not installed
} else {
   # FOO::Bar installed
}
[download]