CGI Web Programming

This is the start of a tutorial about cgi web programming. Everyone is invited to contribute.

A very basic example

Here is an example of a minimal CGI program to demonstrate...

1. Setting a cookie
2. Outputting the content-type (ie make it put out legal text for HTTP)
3. Reading Cookies
4. Reading form data via GET
5. Reading form data via POST

program mini;

uses dos;

var
  a:string;
  c:char;
begin
  //set a cookie (must come before content-type line below)
  //don't forget to change the expires date
writeln('Set-cookie:widget=value; path=/; expires= Mon, 21-Mar-2005  18:37:00 GMT');

  //output legal http page
  writeln('Content-Type:text/html',#10#13);

  //demonstrate get cookies
  a:= GetEnv('HTTP_COOKIE');
  writeln('cookies:',a);
  
  //demonstrate GET result
  a:='';
  a:= GetEnv('QUERY_STRING');
  writeln('GET: ',a);
	
  //demonstrate POST result 
  a:='';
  while not eof(input) do
  begin
     read(c);
     a:= a+c;
  end;	 
  writeln('POST: ',a);
end. 

A simple hitcounter

The application hitcounter presents a simple hitcounter for your website. It is possible to enter blocklists in a configfile so robots and perhaps your own computer are excluded from the statistics. There are still a lot of improvements possible ofcourse like setting a cookie so you get only one hit per session, but it gives a good introduction into CGI programming. If you use the code and modify it, please send me a patch so I can update it.

You can find the code here: [1]

Existing CGI Frameworks

There are existing CGI units and frameworks that make working with CGI trivial (and allow one to set cookies, sessions, retrieve POST and GET). See Powtils

There is also a CGIModule for lazarus, and a few CGI and HTML units in the freepascal FCL.