Under the POSIX standard, it's also possible to use longer, more readable command-line options, preceded with a double dash, as in the
following example:

$ ls --color

The Getopt::Long.pm module provides an API for Perl developers to capture these long command-line options, and act on them within the business logic of the Perl script. This API is pretty advanced: it ignores case differences in option names, can resolve abbreviated option names to their longer counterparts (so long as they are unique), and  recognizes both single- and double-dashes as option prefixes. For purists and those who are tasked with porting legacy applications, the module also supports the older, single-character form of command-line options (but only if they belong to the alphabetic set).

There is one primary function in the Getopt::Long.pm module-GetOptions(), and it serves as the main control point for you to access the options passed to the program. You can use this to

• read command-line options into Perl scalars, arrays or hashes,
• create user-defined subroutines to handle specific options,
• separate option "bundles" into individual units,
• and configure the behaviour of the module.

More on some of these as we proceed through this tutorial.

Getopt::Long.pm is written in the best traditions of object-oriented programming, fondly known as OOP. If you're a fan of OOP, you can create a Getopt::Long object, which has its own methods and properties, and use standard OO syntax to access its functions, extend it, sub-class it, derive new hybrids from it--all kinds of good stuff, basically. In case you don't know what OOP is, you're probably not impressed. Good for you!