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2.4 Option Arguments ¶

Options can take arguments and environment variables can have values (see Parsing the Environment). Some options and environment variables require arguments or values, while others may optionally take arguments or have values, while still others might take no arguments at all or not allow any values. Mu supports all of these types of options and environment variables through the has_arg field of the MU_OPT structure (see Option Structure).

Enumerated Type: enum MU_OPT_HAS_ARG ¶

MU_OPT_NONE ¶

This indicates that an option takes no arguments. If the MU_OPT_BUNDLE flag (see Option Parsing Flags) is not specified, then any text following a short option which doesn’t take an argument will be an error.³ An ‘=’ is an error in a long option that does not take an argument, because ‘=’ is used to specify arguments to long options.

*has_arg will always be set to 0 if has_arg is not NULL.

MU_OPT_OPTIONAL ¶

This indicates that an option may take an argument, but that the option doesn’t require an argument. Even if the MU_OPT_BUNDLE flag is passed (see Option Parsing Flags), short options with optional arguments may not be bundled except as the last option in a bundle. The reason for this is as follows: Suppose short option b takes an optional argument. And suppose short options a and c take no argument. Now what should -abc mean (assuming MU_OPT_BUNDLE was passed)? Is it three options without arguments, a, b, and c? Or is it two options, a and b, the latter of which taking an argument, ‘c’? It is in fact the latter, two options a and b, with b taking an argument, ‘c’. Note, however, that if b is specified as the last option like so: -acb, there is no ambiguity, because there is nothing following the b option (and if there is text following it in another argument, it will be treated as a positional argument; see below).

Short options taking an optional argument must have their arguments specified with the option itself. For example, if a short option, b, takes an optional argument, it must be specified as -barg, not -b arg. The reason for this is because -b arg could be a short option b with an argument arg, or a short option b with no argument, and a positional argument arg. Likewise, long options taking optional arguments must be specified as --long=arg, not --long arg.

If has_arg is not NULL, then *has_arg will be set to 1 if the option has an argument, or 0 if the option doesn’t have an argument.

MU_OPT_REQUIRED ¶

This indicates that an option requires an argument. If no argument is specified, it is an error. Like short options with optional arguments, short options with required arguments may not be bundled except as the last option in a bundle. See above for an explanation.

For short options with required arguments, the argument may be passed with the option itself like so: -rarg, or immediately after the argument like so: -r arg. Arguments to long options with required arguments may also be specified with the option itself like so: --required=arg, or immediately after the argument like so: --required arg.

*has_arg will always be set to 1 if has_arg is not NULL.

• Option Argument Types