Environment variables are useful for gathering data about a client’s system settings, but different servers have different environment variables available to them. To find out what environment variables are available on your Web server, put the following Perl script in your cgi-bin directory and view it in a browser:

 #!/usr/local/bin/perl                           # (or whatever the path is on your server)print "Content-type: text/html

";foreach $key (sort keys %ENV) {        print "$key: $ENV{$key}

";}exit;