CGI environmental variables

				
I'm aware this is well known, but I find it very useful information. No tutorial I have ever read has covered these in depth (I have not read every tutorial though.) This is good for beginners who wish to help improve their website.

CGI's come with environmental variables, variables which store information about the user, the host machine, and the script. Here is how they are employed:
$ENV{'ENVIRONMENT_VARIABLE'};

For instance, if you wanted to manipulate the variable which stores the user's IP address, you would call $ENV{'REMOTE_ADDR'};To use one of the ones below, follow the above format and only use the text that's bolded where the variable name should go. Enough said, on with some examples.

REMOTE_ADDR: Stores the IP address of the person who requested the document.
REMOTE_PORT:Stores the port number from which the page is requested. I'm not sure what this is exactly, since it's for me never been the same as the port the host is on and generates a new number each time I run the script (after closing the web browser first). An interesting effect none the less.
SERVER_NAME:Stores the name of the host that the script is on.
SERVER_SOFTWAREStores the name of the program that the host uses to serve web pages.
SERVER_PORT:The port from which the host is serving the web pages.
ALL_HTTP: Stores the headers that the web browser sent to the script.
AUTH_TYPE: The type of authentication used to verify the user's identity, if any.
AUTH_USER:This displays the username the user entered if they were required to authenticate themselves to access the script. There is also a REMOTE_USER variable, but I have failed to experiment with this.
QUERY_STRING: Stores all of the characters which appear in the URL after the question mark.

Your server also likely has it's own environmental variables. For these, you will need to check out your server's documentation. They are called in the same manner as CGI environmental variables. Lets say you want to print the user's IP address to the screen. The command would go like this:

print "$ENV{'REMOTE_ADDR'}";

Enjoy.