String Options

Options that require a string value are treated specially because the empty string is sometimes allowed as a choice. Here are the differences:

1. setenv OPTION (no value set) will set the option to the empty string. For other options, this is treated as if the environment variable is not set at all.

2. setenv OPTION ' ' does the same as above.

3. Typing ' ' at the prompt sets the option to an empty string.

4. If the option has no default and the user hits return, the option will be set to the empty string (, the empty string is the default for string options which appear to have no default).