Perl for Web Site Management

Controlling a Multistage CGI Script

The next interesting section of the script is a long chain of unless-elsif blocks that test the contents of the $action variable, and execute various subroutines based on what’s in there. The idea here is to have a single CGI script that will carry out a whole sequence of actions as a user clicks his way through multiple dynamically generated pages, with the passed action parameter controlling which part of the script is run for each invocation:

unless ($action) {
    &show_links;
} elsif ($action eq 'show_student_form') {
    &show_student_form;
} elsif ($action eq 'show_leader_form') {
    &show_leader_form;
} elsif ($action eq 'Create student page') {
    &post_student_page;
} elsif ($action eq 'Create leader page') {
    &post_leader_page;
} elsif ($action eq 'regenerate_site_links') {
    &regenerate_site_links;
} else {
    $err_msg = "<LI>Wacky 'action' param '$action'. Shouldn't be able 
               to get here.";
}

I’ve had people tell me that my use of unless-elsif is evil, but it makes sense to me when I read it out loud. Your mileage may vary.

The overall gist of this script is that each unless-elsif block will load up the $content variable with a different page to be delivered back to the requesting user. If anything goes wrong, a descriptive error message will be stuck in the $err_msg variable. After all the unless-elsif stuff is done, the script will check for the presence of anything in $err_msg, and if something is there, it will create an HTML error message incorporating ...