The fields long_opt, subopt_name, and env_var of
the MU_OPT structure (see Option Structure) allow aliases
separated by ‘|’. The short_opt field allows aliases to be
specified as multiple characters in the string (which must be terminated
by a null byte).
For example, the string ‘abc’, when specified as the
short_opt field, indicates three equivalent short options:
-a, -b, and -c. In the long_opt field,
‘foo|bar|baz’ would specify three equivalent long options:
--foo, --bar, and --baz. The same goes for
subopt_name and env_var (but see Parsing the Environment for more information on environment variable aliases).
Duplicate aliases are not allowed, and will be diagnosed as an
error. For example, in the short_opt field, ‘abcb’ will be
diagnosed because the ‘b’ is repeated. Likewise, ‘foo|bar|foo’
would be diagnosed in any of the long_option, subopt_name,
or env_var fields. Empty aliases are diagnosed as well (including
the entire string being empty). So ‘foo||bar’ would be diagnosed in
any of the long_option, subopt_name, or env_var
fields, because there is an empty alias between ‘foo’ and
‘bar’. In any of the same fields, in addition to short_opt,
the empty string (‘’) will be diagnosed as well. Leave a field as
NULL if you don’t want any options (or environment variables) of
that type.