JupiterCrash makes a point (++). However I feel the need to explain why this may be an issue:

What sort of web server are you using?

Assuming you use Apache, the environment varialbes available to your script are limitted for security reasons. This would explain why a script runs from the shell, but fails as a CGI. Again, assuming you use apache, look at the "SetEnv" and "PassEnv" config parameters. If this is the problem, a simple modification of your httpd.conf file, and a bounce of apache will solve all your wows.

If you are not using apache, investigate the configuration of your webserver.

Update Apparently your problem is solved by a previous response, but it is still good to understand the difference between the ENV varialbe avaiable from the shell, versus those passed to a CGI from your web server.