Using Environment Variables

Another way to get input is through the use of environment variables. These are set outside the program, but can be read in pretty easily. For example, let's say we want to read the value of the Query String in the URL (the part after the ?). Let's say the URL was:

http://yoursite.com/cgi-bin/testenv.cgi?cool

You could grab the "cool" bit off the URL and assign it to a variable like this:

$iscool= $ENV{QUERY_STRING};

Using the $ENV{NAME} command, we can do the same to get other environment variables. We just replace the NAME with what we want to get, so:

$userip= $ENV{REMOTE_ADDR};

This will get the IP address of the user, which is useful in tracking a count for your unique visitors. Some other useful environment variables are listed below:

Name	What it Gets
CONTENT_LENGTH	Number of characters submitted from a POST command
HTTP_REFERER	URL user came from, if available.
HTTP_USER_AGENT	Type of Browser viewer is using, if available.
QUERY_STRING	String in URL after the ? character
REMOTE_ADDR	Remote user's IP address
REMOTE_HOST	Name of user's host, if available.
SERVER_NAME	Name of the local server, like: www.yoursite.com

For more on environment variables, visit CGI 101, Chapter 3 for an excellent listing and tutorial.

Well, that's all for now, see you when I write the next section!