readline: How Completing Works
2.6.1 How Completing Works
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In order to complete some text, the full list of possible completions
must be available. That is, it is not possible to accurately expand a
partial word without knowing all of the possible words which make sense
in that context. The Readline library provides the user interface to
completion, and two of the most common completion functions: filename
and username. For completing other types of text, you must write your
own completion function. This section describes exactly what such
functions must do, and provides an example.
There are three major functions used to perform completion:
1. The user-interface function 'rl_complete()'. This function is
called with the same arguments as other bindable Readline
functions: COUNT and INVOKING_KEY. It isolates the word to be
completed and calls 'rl_completion_matches()' to generate a list of
possible completions. It then either lists the possible
completions, inserts the possible completions, or actually performs
the completion, depending on which behavior is desired.
2. The internal function 'rl_completion_matches()' uses an
application-supplied "generator" function to generate the list of
possible matches, and then returns the array of these matches. The
caller should place the address of its generator function in
'rl_completion_entry_function'.
3. The generator function is called repeatedly from
'rl_completion_matches()', returning a string each time. The
arguments to the generator function are TEXT and STATE. TEXT is
the partial word to be completed. STATE is zero the first time the
function is called, allowing the generator to perform any necessary
initialization, and a positive non-zero integer for each subsequent
call. The generator function returns '(char *)NULL' to inform
'rl_completion_matches()' that there are no more possibilities
left. Usually the generator function computes the list of possible
completions when STATE is zero, and returns them one at a time on
subsequent calls. Each string the generator function returns as a
match must be allocated with 'malloc()'; Readline frees the strings
when it has finished with them. Such a generator function is
referred to as an "application-specific completion function".
-- Function: int rl_complete (int ignore, int invoking_key)
Complete the word at or before point. You have supplied the
function that does the initial simple matching selection algorithm
(see 'rl_completion_matches()'). The default is to do filename
completion.
-- Variable: rl_compentry_func_t * rl_completion_entry_function
This is a pointer to the generator function for
'rl_completion_matches()'. If the value of
'rl_completion_entry_function' is 'NULL' then the default filename
generator function, 'rl_filename_completion_function()', is used.
An "application-specific completion function" is a function whose
address is assigned to 'rl_completion_entry_function' and whose
return values are used to generate possible completions.
Info Catalog
readline: Custom Completers
readline: Completion Functions