What we got here is a classic case of trying to use an environment variable (and a pretty important one !) : just use another variable name to get rid of the error. As some suggested, it is good practice to try to avoid full-uppercase variables.
Environment Variables
There is a couple of environment variables inside Bash, PATH
being one of it.
You can get the list of both environment and shell variables using the set
command.
Source : Environment Variable on Wikipedia