which variables are you wishing to set? If you wish to set it in BASH you would use
then to set the path variable
or whatever path you wish. Use extreme caution for the PATH variable though. Many commands in Red Hat are in the default path. You WILL lose them if you don't watch it. Read the man pages on the PATH variable first. Try export with the command prompt and it won't break the system though.
This will change the default prompt to the username, hostname, time, and working directory.