Learning Perl on Win32 Systems

Passing Parameters via CGI

You don’t need a form to pass a parameter to (most) CGI programs. This feature is convenient because it lets programs be called via simple links, not just by full-blown forms. To test this out, take the original URL and add a question mark followed by the parameter name, an equal sign, and the value desired. For example, the following URL would call the ice_cream script with the flavor parameter set to the value mint:

http://www.SOMEWHERE.org/cgi-bin/ice_cream.plx?flavor=mint

When you point your browser at this URL, the browser not only requests the web server to invoke the ice_cream.plx 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.^[99]

The use statement is somewhat like a #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 ...