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7.5.6.11 Option Argument Optional

The arg-optional attribute indicates that the argument to the option is optional (need not be specified on the command line). This is only valid if the arg-type is string (see Arg Type String) or keyword (see Arg Type Keyword). If it is keyword, then this attribute may also specify the default keyword to assume when the argument is not supplied. If left empty, arg-default (see Default Option Argument Value) or the zero-valued keyword will be used.

The syntax rules for identifying the option argument are:

• If the option is specified with a flag character and there is a character following the flag character, then string following that flag character is the option argument.
• If the flag character is the last character in an argument, then the first character of the next argument is examined. If it is a hyphen, then the option is presumed to not have an argument. Otherwise, the entire next argument is the argument for the option.
• If the option is specified with a long option name and that name is ended with an equal sign character (=), then everything after that character is the option argument.
• If the long name is ended by the end of the argument, then the first character of the next argument is examined, just as with the flag character ending an argument string.

This is overridden and the options are required if the libopts library gets configured with --disable-optional-args.