1. CGI Environment Variables

SERVER_SOFTWARE
The name and version of the information server software answering the request:
SERVER_NAME
The server's hostname, DNS alias, or IP address as it would appear in self-referencing URLs:
GATEWAY_INTERFACE
The revision of the CGI specification to which this server complies. Format: CGI/revision:
SERVER_PROTOCOL
The name and revision of the information protocol this request came in with. Format: protocol/revision:
SERVER_PORT
The port number to which the request was sent:
REQUEST_METHOD
The method with which the request was made:
PATH_INFO
The extra path information, as given by the client:
PATH_TRANSLATED
The server provides a translated version of PATH_INFO:
SCRIPT_NAME
A virtual path to the script being executed, used for self-referencing URLs:
QUERY_STRING
The information which follows the ? in the URL which referenced this script:
REMOTE_HOST
The hostname making the request:
REMOTE_ADDR
The IP address of the remote host making the request:
AUTH_TYPE
If the server supports user authentication, and the script is protects, this is the protocol-specific authentication method used to validate the user:
REMOTE_USER
If the server supports user authentication, and the script is protected, this is the username they have authenticated as:
REMOTE_IDENT
If the HTTP server supports RFC 931 identification, then this variable will be set to the remote user name retrieved from the server. Usage of this variable should be limited to logging only:
CONTENT_TYPE
For queries which have attached information, such as HTTP POST and PUT, this is the content type of the data:
CONTENT_LENGTH
The length of the said content as given by the client:
HTTP_ACCEPT
The MIME types which the client will accept:
HTTP_USER_AGENT
The browser the client is using to send the request:

2. SSI Environment Variables

DOCUMENT_NAME
The current filename:
DOCUMENT_URI
The virtual path to this document:
QUERY_STRING_UNESCAPED
The unescaped version of any search query the client sent, with all shell-special characters escaped with \:
DATE_LOCAL
The current date, local time zone:
DATE_GMT
Same as DATE_LOCAL but in Greenwich mean time:
LAST_MODIFIED
The last modification date of the current document:

2. SSI Computed Variables

LAST_MODIFIED
The last modification date of a given file on the server, for example "La_Silla/missions.r":