Unset an environment variable - the opposite of setenv.
Syntax unsetenv pattern
Removes all environment variables whose names match pattern.
`unsetenv *' thus removes all variables unless they are read-only; this is a bad idea.
It is not an error for nothing to be unsetenved.
"Look Dave, I can see you're really upset about this" - HAL (Space 2001)
unset - Unset a variable