To test a shell script called myscript, the environment variable FOOBAR must be removed temporarily. How can this be done?

The `unset -v FOOBAR` command unsets the variable in the current shell, making the change permanent for the duration of that shell session, not just for `myscript`.

The `set -a FOOBAR=""` command exports `FOOBAR` as an empty string, meaning it still exists in the environment, rather than being removed.

The `env` command can run a program in a modified environment. The `-u` option specifies a variable to unset in the environment for the command being executed, ensuring it's removed only for `myscript` and not in the current shell.

The `env -i myscript` command executes `myscript` with an *empty* environment, meaning *all* current environment variables would be discarded, not just `FOOBAR`.