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Each browser request creates a set of read-only variables that store data about the actual browser and server transactions.
For example, these variables store relevant IP addresses and the browser type that's being used for the client request.
We refer to these variables as CGI environment variables even when the Web server uses an API instead of CGI to communicate with ColdFusion Server.
You can reference CGI environment variables anywhere in a page, for example, to perform conditional processing based on the type of browser that requested the page.
Different browsers and servers support different CGI variables. The table below describes the most common CGI environment variables that are created on the server or created on the client and passed to the server in the request (HTTP) header.
| CGI Server Variables | Description | Server or Client |
|---|---|---|
| CGI.SERVER_SOFTWARE | The information server software name and version that answers the browser request. | Server |
| SERVER_NAME | The server's hostname, DNS alias, or IP address as it appears in self-referencing URLs. | Server |
| GATEWAY_INTERFACE | The CGI specification revision to which the server complies. | Server |
| SERVER_PROTOCOL | The information protocol name and revision associated with the browser request. | Server |
| SERVER_PORT | The port number that received the request. | Server |
| REQUEST_METHOD | The HTTP request method. For example, Get or Post. | Server |
| PATH_INFO | Extra path information that's supplied by the client. | Server |
| PATH_TRANSLATED | A translated version of PATH_INFO supplied by the server. | Server |
| SCRIPT_NAME | The virtual path to the script being executed. This is used for self-referencing URLs. | Server |
| QUERY_STRING | The query information that follows the question mark (?) in the URL that referenced the script. | Server |
| REMOTE_HOST | The requesting machine's hostname when available. | Server |
| REMOTE_ADDR | The requesting machine's IP address. | Server |
| AUTH_TYPE | The protocol-specific authentication method used to validate users when supported on the server and when the script is protected. | Server |
| REMOTE_USER AUTH_USER | The username that the server authenticated when supported on the server and when the script is protected. | Server |
| REMOTE_IDENT | The remote username that's retrieved when the HTTP server supports RFC 931 identification. This variable can be used for logging only. | Server |
| CONTENT_TYPE | The content type of attached query data. Such as information attached via HTTP POST and PUT, | Server |
| CONTENT_LENGTH | The length of the content as described by the client and sent to the server. | Server |
| HTTP_REFERER | The referring document that linked or submitted form data to this page. | Client |
| HTTP_USER_AGENT | Browser type and revision information for the sending request. | Client |
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Note: | ColdFusion stores an empty string value for a CGI variable when detailed information is not available for a particular session. For this reason, when performing conditional processing based on a CGI variable, test for null (") rather than a variable's existence. |
You will learn about conditional processing in Chapter 8, Programming with ColdFusion.
Reference CGI environment variables anywhere on a page to use their values. As with any variable that you reference:
The code below outputs the current value of the HTTP_USER_AGENT to display the browser type and version:
<CFOUTPUT>
#CGI.HTTP_USER_AGENT#
</CFOUTPUT>
As you can see, you reference and output CGI variables using the same procedure that you follow when outputting local variables. Move on in this chapter to learn about how you work with and output cookie variables.
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