Today, almost every web site contains highly interactive and dynamic web pages in order to make internet more captivating and to support e-commerce. Users can perform various tasks on the World Wide Web like chatting, polling, blogging, shopping, gaming, audio/video streaming and much more. In order to interact with the user in real time, web browsers need to connect with web servers frequently especially when a user is doing online banking. In that case the customer’s data is updated instantly. There is no space for delay or any other kind of web error. So, in order to facilitate such a high level of user interactivity on the internet, CGI (Common Gateway Interface) was developed. CGI is a standard which specifies the way for web servers to communicate wit the external programs/scripts and vice versa. CGI allows the information to effectively travel between the web browser, web server and any other external script or application (applets) which is needed to perform some specific tasks on the web.
CGI fully supports the functioning of dynamic pages. In fact the DHTML is of no use without CGI standards. CGI can be used to perform various dynamic tasks such as a hit counter, online banking, online polling, video conferencing etc. It has become very popular now a days because of the following reasons:
1) CGI is the quickest way to support dynamic pages.
2) CGI standards are supported by most of the web browsers. Thus there are no compatibility issues.
3) CGI codes are available easily. There are lot of codes each written for a specific purpose.
The basic CGI programs can be easily written in C, C++, Shell scripts and Perl language. Every CGI program has its own ‘Method’ of communication, processing and functioning. In total there are three methods which can be used:
1) GET Method
2) POST Method
3) HEAD Method
The GET Method is used you want that the CGI program should receive the data/query. After receiving the query data the CGI program interprets it and executes the expected tasks. GET Method should be used when you want to retrieve the data from the web server which you will not change. On the contrary, POST Method is used when you want to send data to the web server which will change the existing one or when you want to send large amount of data to the CGI program.
There is one more CGI Method called HEAD. It is similar to the GET Method, but while using the HEAD the web server only sends the HTTP headers instead of the actual data to the web browser.
CGIs are widely used for web site linking. It facilitates the search capability within a website. For example; at yahoo.com one can search for any resource in the search bar. Here the yahoo’s web page acts as a front end panel where the user can specify the search criteria and at the backend the web page is linked with the databases via CGI.
Now a days, as the Java language is also being used for web sites, there are chances that CGI will become obsolete after sometime because Java provides better options and its processing time is less than CGI programs.