Perl Inter-Application Libraries

Perl Inter-Application Libraries

Good design does not stop with the use of subroutines. Often, several different scripts will be designed to incorporate the use of similar routines. In this case, it makes sense to remove the common routines from the programs and place them in a separate file of routines.
This file can then be loaded as a library of subroutines into each program as needed.
For example, in CGI, most applications will need a form gathering and parsing routine, a template for sending out the HTTP header, and perhaps one to generate template HTML code, such as the following:
```
<HTML>
  <HEAD>
    <TITLE>My Script Title</TITLE>
  </HEAD>
<BODY>
```
In this case, we use library files and require them from the main script. A library file in Perl is simply a text file containing subroutines that are shared by several different Perl scripts. For these library files to be usable by the program, they must be readable by the script and must be in the Perl library path (or its location must be explicitly referenced).
For example, if we wanted to load Steven Brenner's cgi-lib.pl library into our script, we would use the following:
```
require "cgi-lib.pl";
```
When this is done, every subroutine in cgi-lib.pl becomes accessible to the main script as if it were actually written into the script's code. We simply reference a subroutine contained in cgi-lib.pl as we would any other subroutine in the main program.