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(libc.info)Argp Help Filtering

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Customizing Argp Help Output
----------------------------

   The `help_filter' field in a `struct argp' is a pointer to a
function that filters the text of help messages before displaying them.
They have a function signature like:

     char *HELP-FILTER (int KEY, const char *TEXT, void *INPUT)

Where KEY is either a key from an option, in which case TEXT is that
option's help text.  Note: Argp Option Vectors.  Alternately, one of
the special keys with names beginning with `ARGP_KEY_HELP_' might be
used, describing which other help text TEXT will contain.  Note: Argp
Help Filter Keys.

   The function should return either TEXT if it remains as-is, or a
replacement string allocated using `malloc'.  This will be either be
freed by argp or zero, which prints nothing.  The value of TEXT is
supplied _after_ any translation has been done, so if any of the
replacement text needs translation, it will be done by the filter
function.  INPUT is either the input supplied to `argp_parse' or it is
zero, if `argp_help' was called directly by the user.

Keys

Argp Help Filter Keys. Special KEY values for help filter functions.