The `importas` program

importas replaces a literal with the value of an environment variable, then executes another program.

Interface

     importas [ -i | -D default ] [ -u ] [ -s ] [ -C | -c ] [ -n ] [ -d delim ] variable envvar prog...

importas fetches the value of envvar in the environment. If neither the -D nor the -i option is given, and envvar is undefined, the null word is returned.
importas then performs variable substitution on prog..., with variable as key and that string as value.
importas then execs into the modified prog....

-D default : If envvar is undefined, and this option is not given, substitute zero word for variable instead of the empty word; and if it is given, substitute default instead. To substitute the empty word, use -D "".
-i : Insist. If envvar is undefined, importas will not do anything; instead, it will exit 100 with an error message. This has precedence over any -D option.
-u : Unexport. envvar will be removed from the environment after the substitution. importas -u variable envvar is equivalent to importas variable envvar unexport envvar.
Other options are used to control the substitution mechanism.