CGI

The Common Gateway Interface is a method for generating web pages dynamically.
Instead of interpreting the argument of GET (or POST) as a filename, its interpreted as a program name with arguments.
The URL for a GET is interpreted as programname?parameter1=value1&parameter2=value2&..... The values are optional. The parameters and values are passed as command-line arguments to the program.
For a POST, all the parameters and values are passed to the program in the standard input. That is, as thought a person had first run the program and then typed the information on the keyboard.
The program is run and whatever it prints out is sent back to the client.
CGI programs run as independent processes and so have many drawbacks:
- They consume a lot of system resources.
- They suffer from startup delays.
- It is hard to maintain state between successive calls (must write to file).
It is because of these reasons that server-side systems were introduced. These include Java servlets, PHP, Zope, IBM's Websphere, etc.