Learning Perl, Second Edition

19.4. Passing Parameters via CGI

You don't need a form to pass a parameter to (most) CGI programs. To test this, change the URL to http://www.SOMEWHERE.org /cgi-bin/ice_cream?flavor=mint

When you point your browser at this URL, the browser not only requests the web server to invoke the ice_cream program, but it also passes the string flavor=mint to the program. Now it's up to the program to read the argument string and pick it apart. Doing this properly is not as easy as you might think. Many programs try to wing it and parse the request on their own, but most hand-rolled algorithms only work some of the time. Given how hard it is to get it right in all cases, you probably shouldn't try to write your own code, especially when perfectly fine modules already handle the tricky parsing business for you.

Enter the CGI.pm module, which always parses the incoming CGI request correctly. To pull this module into your program, merely say

use CGI;

somewhere near the top of your program.^[5]

^[5] All Perl modules end in the suffix ".pm"; in fact, the use statement assumes this suffix. You can learn how to build your own modules in Chapter 5 of Programming Perl or the perlmod (1) manpage.

The use statement is like an #include statement in C programming in that it pulls in code from another file at compile-time. But it also allows optional arguments specifying which functions and variables you'd like to access from that module. Put those in a list following the module name in the use statement. ...