There’s some common functionality found in many places like help, parsing values, sorting, extensible arrays, etc. Not all places are unified and use old code implementing it manually. Below is list of usable APIs that should be spread and updated where it’s still not. A need for new API might emerge from cleanups, then it should appear here. The text below gives pointers and is not extensive, search the definitions and actual use in other code too.
Global options need to be processed and consumed by clean_args_no_options, argument count by check_argc_*, usage_* for handling usage.
Options are parsed by getopt or getopt_long. Individual values from options are recognized by parse_*, basic types and custom types are supported.
Size unit pretty printing
Many commands print byte sizes with suffixes and the output format can be affected by command line options. In the help text the options are specified by either HELPINFO_UNITS_SHORT_LONG (both long and short options) or just HELPINFO_UNITS_LONG in case the short option letters would conflict.
Automatic parsing of the options from argv is done by get_unit_mode_from_arg. Printing options is done by pretty_size_mode which takes the value and option mode. Default mode is human readable, the macros defining the modes are from UNITS_* namespace.
Undocumented or incomplete APIs: