Common Gateway Interface: An Overview In 7 Easy Points

Ajay Ohri


With the advent of technology and the Internet explosion, companies are starting to find it tedious to run a business without an enticing web page that would hold a potential customer’s attention and his ever-changing needs. The need for a server-side dynamic web page is fulfilled when different content is displayed each time a web page is viewed. This is possible through the Common Gateway Interface (CGI).

The CGI in itself isn’t a search engine. It is a way to interface programs such as that of search engines with web servers. Common Gateway Interface is used for a simple interactive application. A few examples of such applications include Guest books that allow users to leave messages for the public to see, email forms, feedback forms, registration forms, mailing list maintenance, blogs, Colouring book, etc.

In this article, we’ll see,

  1. What is Common Gateway Interface?
  2. How Common Gateway Interface works?
  3. Features of Common Gateway Interface
  4. Advantages of CGI
  5. Disadvantages of CGI
  6. Required skills
  7. Who is the right audience for learning CGI technologies?

1. What is Common Gateway Interface?

In computing, Common Gateway Interface commonly known as CGI is an interface specification for web servers to execute programs running on a server that generates web pages dynamically, creating a customized response based on the request received from the client or user.  The CGI provides middleware between WWW servers and external databases and information sources. The Worldwide Consortium (W3C) defined CGI and also defined how a program interacts with the HTTP server.

In brief, the web server passes information from a small application program that processes data and sends back information in a consistent manner. This means that the person who has written the application program can ensure that the application is used no matter which operating system the server uses (PC, Macintosh, UNIX, or others). This application that processes the passing of data back and forth is known as Common Gateway Interface (CGI).

2. How Common Gateway Interface works?

If one is creating a website and wants a CGI application to control it, the name of the application must be specified in the URL. This has to have been coded in an HTML file. 

The web server will analyze the URL and looks for the file name. Otherwise, it activates the gateway program mentioned in the URL and sends parameters to the program via the URL.

It must be noted that for the Common Gateway Interface script to work, the webserver needs to support it. 

To generate a response as per the request, a Common Gateway Interface program calls other applications on the server to create a user-specific response. After executing said operations, the CGI program returns the output to the web server, which then forwards the same response to the client/ user. 

3. Features of Common Gateway Interface

Certain prominent features of Common Gateway Interface include

  • It is an application that is very well defined and has a supported standard.
  • CGI is generally written in comprehensible scripts such as Perl, PHP, UNIX Shell, C language, Visual Basic, C# or maybe just a simple shell script.
  • This technology interfaces with HTML.
  • It is the best method to create a counter as it is currently the quickest application that is available in the market.
  • The CGI standard is generally the most compatible with the current browsers on the internet.

4. Advantages of CGI

  • It is easier to perform advanced tasks on CGI in comparison to performing the tasks on Java.
  • It is easier to use a prewritten code like CGI than to create/ write a code from scratch on your own.
  • CGI provides interactivity to a web application and enhances user experience.
  • CGI programs are cost-effective, and their use will reduce business’ development costs.
  • Common Gateway Interface allows for the programs to be written in any language and on any platform as long as it conforms to the specification that has been set out.
  • A multitude of CGI-based counters and codes to perform simple tasks are available.
  • As CGI applications run on the server, they are very secure.
  • CGI applications are lightweight and speedy as there is no specific particular library requirement that comes with creating a CGI program.

5. Disadvantages of CGI

There are certain disadvantages to this easily comprehensible and user-friendly application, such as:

  • In Common Gateway Interface, each page load incurs overhead charges by having to load the programs into memory.
  • Under normal circumstances, data cannot be easily cached between page loads.
  • Common Gateway Interface is time-consuming as it takes a lot of processing time.
  • A vulnerable CGI can exploit the host system allowing the attacker to access any CGI on the host system. In turn, this would entail security issues such as viewing of files, denial of service attacks against the host, privileges to manipulate the web browser, etc.

6. Required skills

Common Gateway Interface programs are essentially language-independent, but you can write them in any language and make them work in any environment. A few programming languages that fit to create the CGI scripts are Perl, PHP, UNIX Shell, C language, Visual Basic, C#, Python, and Java. Thus, if someone has high-level proficiency in any of these languages, they can easily learn the CGI model.

7. Who is the right audience for learning CGI technologies?

  • PHP Developers: PHP is the main objective of Web development and for the scripting of server-side language. A PHP interpreter typically prepares the PHP code that has been implemented as both a web server module and an executable Common Gateway Interface (CGI). The web server application incorporates the result of the PHP software, which can be all kinds of data, such as images while using the web page. The PHP code can be executed with a CGI model and is used for standalone visual software applications.
  • Android Developers: Android is the most well-known mobile operating system. Developed by Google and open source as well. CGI script comes very beneficial for android developers.
  • IoT Developers: The Internet of Things like smartphones and other devices are embedded in the systems using c and c++ language to interact with hardware and software using the CGI model.

However, it must be noted that there are ways to prevent CGI attacks. While creating CGI programs, one can ensure that there is an error-handling code that notifies when other than normal permissions are required. One can set restrictions on file permissions, make sure that the web browser is not run with root privileges, to delete unused scripts to reduce vulnerability. Deploying Intrusion Detection and Host Intrusion detections can be done as well to alert in case of discrepancies. At the end of the day, one must ensure that security policies are in place while employing a CGI application to keep one’s website dynamic.


The need to understand and adapt to CGI in the present circumstances is quite crucial. Not only is this essential to keep up with the dynamic e-commerce market, but it also provides for career opportunities.  For example, one can get into web development or master Python Script.

However, one must note that the first-generation CGI model is fairly older and is updated by several programming languages, including PHP. It has turned into a relatively basic tool and can be substituted by a self-contained HTTP server running behind a reverse proxy. This HTTP server can provide one with all the necessary information in a more reliable and consistent manner. However, Fast CGI is an excellent and beneficial alternate protocol. It uses long-term processes to handle a number of requests rather than making a new system for each request. This improves the running speed and reduces the production timeframe.

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