CGI programming allows web servers to interface with external applications to dynamically generate web page content. There are two main methods for passing information to CGI scripts: GET, which encodes variables in the URL, and POST, which encodes variables in the HTTP request body. All data passed to the server is URL encoded for platform independence. A basic CGI script structure includes initialization to check the request method and parse variables, processing the input data, and termination to release resources.

1. CGI PROGRAMMING

2. CGI PROGRAMMING
Introduction
1 CGI stands for Common Gateway
Interface
2 Script language
Unix shell script & perl
3 Interactive programming

3. APACHE DIRECTORY STRUCTURE
 CGI-BIN
 Conf
 Htdocs
 Icons
 Images
 logs

4. STRUCTURE OF CGI SCRIPT
 Two way of passing information
1.GET METHOD
2.POST METHOD
Environmental Variable
1: REQUEST METHOD

5. GET REQUEST METHOD
Introduction
Example: http://myserver.edu/cgi-bin/myprog.pl?
name=niloy&rollno=7312&age=24
Environmental Variable
QUERY_STRING.

6. POST REQUEST METHOD
Introduction
Standard Input
Format: var1=value1&var2=value2&……
Environmental Variable:
CONTENT_LENGTH.

7. URL ENCODING
For platform independence, all data passed to the server are
URL-encoded.
Some rules of encoding:::::
 Variables are separated by ‘&’.
 List of special character “+”, “()” “[]” etc
 Special character can escaped using two hexa decimal
Number

8. BASIC STRUCTURE OF CGI SCRIPT
Step 1: Initialization
 Check REQUEST_METHOD
 Parse string and extract variables depending
on “GET” or “POST”.
 Check CONTENT_TYPE, to find out if
the string is URL-encoded.

9. BASIC STRUCTURE OF CGI SCRIPT
Step 2: Processing
 Process the input data.
 Output the results (MIME-type header, and the
contents).

10. BASIC STRUCTURE OF CGI SCRIPT
Step 3: Termination
 Release the system resources.
 Terminate the program.