setenv
(setenv name value)
The setenv function assigns a new value to a specified operating system environment variable.
Arguments
name is a string specifying the name of the environment variable to be set. Environment variable names must be spelled and cased exactly as they are stored in the system registry.
value is a string specifying the value for name.
Return Value
The function returns the value of value if it succeeds; otherwise, it returns nil.
(setenv "MY_ENVVAR" "TIME")
"TIME"
An environment variable can be reset by assigning it "".