Re: learning by example; please explain what this code is doing?

You can reduce your script to a minimal example for learning:

use strict;
use CGI '3.30', ();
my $q = CGI->new;

sub GET($$) {
    my ($path, $code) = @_;
    return unless $q->request_method eq 'GET' or $q->request_method eq
+ 'HEAD';
    return unless $q->path_info =~ $path;
    $code->();
    exit;
}

eval {

    GET qr{^/=$} => sub {
        print $q->header('text/html');
        print $q->h1('REST API Documentation');
    };

    GET qr{^/=/model/book/id/([\d-]+)$} => sub {
        my $id = $1;

        # Look up the resource file
        my $filename = get_local_path($id);
        if (-f $filename) {
            ..
        };
    };

};
if( $@ ) {
    print "There was an error.";
};
[download]

Each call to GET gets passed a regular expression and a piece of code to call. The GET routine will then check whether the request matches that regular expression and if it does, call the callback to produce the result.

All of this is not related to the CGI module at all, except for where the request comes from.

To familiarize yourself with the code, I would start with (a copy of) the program and rip out as much of CGI as possible and run it from the command line. Add print statements to see where the code goes through and what it looks at.

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Re^2: learning by example; please explain what this code is doing? by Habs (Acolyte) on Mar 30, 2016 at 13:05 UTC
Hello Corion Thank you for that; very helpful and good point on slimming down the code. I am struggling to see what gets passed and from where, for those routines to get called; I will do as you say and get it to run from the command line and see if that helps me further appreciate. Regards	[reply]
Re^3: learning by example; please explain what this code is doing? by Your Mother (Archbishop) on Mar 30, 2016 at 13:14 UTC
I recommend these for starting to unravel where everything is happening. CGI#FETCHING-ENVIRONMENT-VARIABLES Security-focused HTTP Primer perlsub (anonymous subroutines / code references) anonymous subs in Perl via Google Update: Part of what I meant when I said it was not good learning code is that it is idiomatic and full of techniques that I could not call beginner friendly. Explaining it to a newcomer to Perl might require line-by-line analysis and examples.	[reply]


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