What Is CGI in Web Server?


Heather Bennett

What Is CGI in Web Server?

CGI stands for Common Gateway Interface. It is a protocol that allows a web server to interact with external programs or scripts, enabling dynamic content generation on web pages. CGI acts as a mediator between the server and the program, facilitating data exchange and processing.

How Does CGI Work?

To understand how CGI works, let’s break it down into a few simple steps:

  1. Client Request: When a user requests a web page that requires dynamic content, such as submitting a form or accessing a database, the server receives the request.
  2. Server Interaction: The server identifies that the requested page requires CGI processing and locates the appropriate program or script to handle it.
  3. Data Exchange: The server sends user-provided data from the request (e.g., form input) to the CGI program or script for processing.
  4. Data Processing: The CGI program processes the received data and generates dynamic content based on predefined instructions.
  5. Data Response: The generated dynamic content is sent back to the server for further handling and delivery to the client.
  6. Client Response: Finally, the server delivers the processed content back to the user’s browser, which displays it on their screen.

The Role of CGI Scripts

In order for CGI to work effectively, developers create scripts written in languages such as Perl, Python, Ruby, or shell scripting. These scripts contain instructions for processing data received from users and generating appropriate responses. The output can be simple text, HTML code, images, or even files for download.

CGI scripts are typically placed in a designated directory on the server, often named “cgi-bin.” This directory is configured to allow execution of scripts and restrict access to prevent unauthorized use.

Common Uses of CGI

CGI is widely used for various purposes, including:

  • Form processing: Collecting and processing data submitted through web forms.
  • E-commerce: Handling online transactions and payment gateways.
  • Database access: Retrieving and updating information stored in databases.
  • User authentication: Verifying user credentials for restricted areas of a website.
  • Dynamic content generation: Creating personalized web pages based on user input or preferences.

Advantages and Disadvantages of CGI


  • Compatibility: CGI can be used with any web server that supports the CGI protocol, making it highly versatile.
  • Language independence: CGI scripts can be written in various programming languages, allowing developers to choose their preferred language.


  • Performance overhead: Each CGI request creates a new process, which can impact server performance when handling multiple simultaneous requests.
  • Lack of scalability: As the number of concurrent users increases, CGI scripts may become less efficient due to process creation overhead.

In Conclusion

CGI is an essential component of web server technology that enables dynamic content generation. By facilitating communication between servers and external programs or scripts, CGI allows websites to incorporate interactive features and process user input effectively. Understanding how CGI works and its potential uses can empower developers to create more engaging and interactive web applications.

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