An Introduction to CGI - The Common Gateway Interface

Request Methods

While several methods are defined in the HTTP specification, only two are commonly used for CGI. The first is GET, the second is POST. Other methods specified in HTTP 1.1 (see RFC 2068 at http://www.w3c.org/P rotocols/rfc2068/rfc2068) include OPTIONS, PUT, HEAD, DELETE, and TRACE. You can tell which method was used by inspecting the environment variable REQUEST_METHOD. As a rule of thumb, any time the request is the result of a user clicking on a link or directly entering a URL, the request method is GET. When the request is the result of a form submission, the request method is the same as the value of the method attribute in the form tag of the html document containing the form. Note that HTTP request methods are case-sensitive.

Many people write or use pre-written libraries that aid in retrieving the input for their gateway program. At minimal, such a library should provide functions for automatically determining the request method and retrieving the input; however, most libraries go far beyond this minimal functionality. You should seek out such libraries to assist you in writing your code; they will help you avoid common pitfalls and bugs and more importantly some of the more subtle security holes.

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