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What kind of environment variables does a web context provide?
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There are three classes of environment variables:
- Server specific environment variables
- Script specific environment variables
- Request specific environment variables (read from the headers)
Server specific environment variables
The first group of environment variables are server-specific and be the same value for any request.
| Variable Name | Description | Example |
| SERVER_SOFTWARE | The name and version of the server software answering the HTTP request. | Apache/2.0 |
| SERVER_NAME | The server hostname. This could also be the DNS alias or IP address. | MACHINE_42 |
| GATEWAY_INTERFACE | The CGI revision that this server complies with. | CGI/1.1 |
Script specific environment variables
The next group of environment variables are specific to the script, so expect them to vary.
| Variable Name | Description | Example |
| SERVER_PROTOCOL | The name and version number of the protocol that called the script. | HTTP/1.0 |
| SERVER_PORT | The port number for the script. | 80 |
| REQUEST_METHOD | The method for the CGI request. | GET (or POST, or HEAD) |
| PATH_INFO | Any extra path information that follows the script path in the URL. If present, it is passed as an argument to the script. For instance, http://hostname/cgi-bin/EnvVars.cgi/PathInfo | /PathInfo |
| PATH_TRANSLATED | A virtual-to-physical mapping of PATH_INFO, which can be used directly as an absolute path or file. | hostname\cgi-bin\PathInfo |
| SCRIPT_NAME | A virtual path to the script. Useful if you output HTML code that refers back to the script. | /cgi-bin/EnvVar.cgi |
| QUERY_STRING | A key variable when using METHOD=GET from your web page. It contains the information following '?' in the URL, and passes it to the script. For instance, http://hostname/cgi-bin/EnvVars.cgi?QueryString | QueryString |
| REMOTE_HOST | The hostname making the request. If it is not available, then the IP address should be in REMOTE_ADDR. This value isn't always set. | hostname.com |
| REMOTE_ADDR | The IP address of the client making the request. | 128.18.32.229 |
| AUTH_TYPE | The protocol-specific authentication method used to validate users. Only used if the server supports authentication. | (varies) |
| REMOTE_USER | If the server supports authentication, and the script is protected, then this value will hold the username of the individual. | (varies) |
| REMOTE_IDENT | This variable is used solely for logging, if the HTTP server supports RFC 931 identification. In those cases, it will be set to the remote user name. | |
| CONTENT_TYPE | For requests made with METHOD=POST, this will be the content type of the data. | |
| CONTENT_LENGTH | The length in bytes of the content being passed (set by the client). |
Environment variables from header lines
These variables are set if there were header lines received from the browser.
| Variable Name | Description | Example |
| HTTP_ACCEPT | The MIME types the client will accept. | 'image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */*' |
| HTTP_USER_AGENT | The browser that the client is using. This is useful if you want to present browser specific pages to your users. If the user has installed additional tools like the Yahoo companion, you'll see that in this field as well. | (Internet Explorer 4.0): Mozilla/4.0 (compatible; MSIE 4.01; Windows 2000;) |
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