rltech.texinfo

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@ifinfo
This document describes the GNU Readline Library, a utility for aiding
in the consitency of user interface across discrete programs that need
to provide a command line interface.

Copyright (C) 1988, 1994 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
pare preserved on all copies.

@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).
@end ignore

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
@end ifinfo

@node Programming with GNU Readline
@chapter Programming with GNU Readline

This chapter describes the interface between the GNU Readline Library and
other programs.  If you are a programmer, and you wish to include the
features found in GNU Readline
such as completion, line editing, and interactive history manipulation
in your own programs, this section is for you.

@menu
* Basic Behavior::	Using the default behavior of Readline.
* Custom Functions::	Adding your own functions to Readline.
* Readline Variables::			Variables accessible to custom
					functions.
* Readline Convenience Functions::	Functions which Readline supplies to
					aid in writing your own
* Custom Completers::	Supplanting or supplementing Readline's
			completion functions.
@end menu

@node Basic Behavior
@section Basic Behavior

Many programs provide a command line interface, such as @code{mail},
@code{ftp}, and @code{sh}.  For such programs, the default behaviour of
Readline is sufficient.  This section describes how to use Readline in
the simplest way possible, perhaps to replace calls in your code to
@code{gets()} or @code{fgets ()}.

@findex readline
@cindex readline, function
The function @code{readline ()} prints a prompt and then reads and returns
a single line of text from the user.  The line @code{readline}
returns is allocated with @code{malloc ()}; you should @code{free ()}
the line when you are done with it.  The declaration for @code{readline}
in ANSI C is

@example
@code{char *readline (char *@var{prompt});}
@end example

@noindent
So, one might say
@example
@code{char *line = readline ("Enter a line: ");}
@end example
@noindent
in order to read a line of text from the user.
The line returned has the final newline removed, so only the
text remains.

If @code{readline} encounters an @code{EOF} while reading the line, and the
line is empty at that point, then @code{(char *)NULL} is returned.
Otherwise, the line is ended just as if a newline had been typed.

If you want the user to be able to get at the line later, (with
@key{C-p} for example), you must call @code{add_history ()} to save the
line away in a @dfn{history} list of such lines.

@example
@code{add_history (line)};
@end example

@noindent
For full details on the GNU History Library, see the associated manual.

It is preferable to avoid saving empty lines on the history list, since
users rarely have a burning need to reuse a blank line.  Here is
a function which usefully replaces the standard @code{gets ()} library
function, and has the advantage of no static buffer to overflow:

@example
/* A static variable for holding the line. */
static char *line_read = (char *)NULL;

/* Read a string, and return a pointer to it.  Returns NULL on EOF. */
char *
rl_gets ()
@{
  /* If the buffer has already been allocated, return the memory
     to the free pool. */
  if (line_read)
    @{
      free (line_read);
      line_read = (char *)NULL;
    @}

  /* Get a line from the user. */
  line_read = readline ("");

  /* If the line has any text in it, save it on the history. */
  if (line_read && *line_read)
    add_history (line_read);

  return (line_read);
@}
@end example

This function gives the user the default behaviour of @key{TAB}
completion: completion on file names.  If you do not want Readline to
complete on filenames, you can change the binding of the @key{TAB} key
with @code{rl_bind_key ()}.

@example
@code{int rl_bind_key (int @var{key}, int (*@var{function})());}
@end example

@code{rl_bind_key ()} takes two arguments: @var{key} is the character that
you want to bind, and @var{function} is the address of the function to
call when @var{key} is pressed.  Binding @key{TAB} to @code{rl_insert ()}
makes @key{TAB} insert itself.
@code{rl_bind_key ()} returns non-zero if @var{key} is not a valid
ASCII character code (between 0 and 255).

Thus, to disable the default @key{TAB} behavior, the following suffices:
@example
@code{rl_bind_key ('\t', rl_insert);}
@end example

This code should be executed once at the start of your program; you
might write a function called @code{initialize_readline ()} which
performs this and other desired initializations, such as installing
custom completers (@pxref{Custom Completers}).

@node Custom Functions
@section Custom Functions

Readline provides many functions for manipulating the text of
the line, but it isn't possible to anticipate the needs of all
programs.  This section describes the various functions and variables
defined within the Readline library which allow a user program to add
customized functionality to Readline.

@menu
* The Function Type::	C declarations to make code readable.
* Function Writing::	Variables and calling conventions.
@end menu

@node The Function Type
@subsection The Function Type

For readabilty, we declare a new type of object, called
@dfn{Function}.  A @code{Function} is a C function which
returns an @code{int}.  The type declaration for @code{Function} is:

@noindent
@code{typedef int Function ();}

The reason for declaring this new type is to make it easier to write
code describing pointers to C functions.  Let us say we had a variable
called @var{func} which was a pointer to a function.  Instead of the
classic C declaration

@code{int (*)()func;}

@noindent
we may write

@code{Function *func;}

@noindent
Similarly, there are

@example
typedef void VFunction ();
typedef char *CPFunction (); @r{and}
typedef char **CPPFunction ();
@end example

@noindent
for functions returning no value, @code{pointer to char}, and
@code{pointer to pointer to char}, respectively.

@node Function Writing
@subsection Writing a New Function

In order to write new functions for Readline, you need to know the
calling conventions for keyboard-invoked functions, and the names of the
variables that describe the current state of the line read so far.

The calling sequence for a command @code{foo} looks like

@example
@code{foo (int count, int key)}
@end example

@noindent
where @var{count} is the numeric argument (or 1 if defaulted) and
@var{key} is the key that invoked this function.

It is completely up to the function as to what should be done with the
numeric argument.  Some functions use it as a repeat count, some
as a flag, and others to choose alternate behavior (refreshing the current
line as opposed to refreshing the screen, for example).  Some choose to
ignore it.  In general, if a
function uses the numeric argument as a repeat count, it should be able
to do something useful with both negative and positive arguments.
At the very least, it should be aware that it can be passed a
negative argument.

@node Readline Variables
@section Readline Variables

These variables are available to function writers.

@deftypevar {char *} rl_line_buffer
This is the line gathered so far.  You are welcome to modify the
contents of the line, but see @ref{Allowing Undoing}.
@end deftypevar

@deftypevar int rl_point
The offset of the current cursor position in @code{rl_line_buffer}
(the @emph{point}).
@end deftypevar

@deftypevar int rl_end
The number of characters present in @code{rl_line_buffer}.  When
@code{rl_point} is at the end of the line, @code{rl_point} and
@code{rl_end} are equal.
@end deftypevar

@deftypevar int rl_mark
The mark (saved position) in the current line.  If set, the mark
and point define a @emph{region}.
@end deftypevar

@deftypevar int rl_done
Setting this to a non-zero value causes Readline to return the current
line immediately.
@end deftypevar

@deftypevar int rl_pending_input
Setting this to a value makes it the next keystroke read.  This is a
way to stuff a single character into the input stream.
@end deftypevar

@deftypevar {char *} rl_prompt
The prompt Readline uses.  This is set from the argument to
@code{readline ()}, and should not be assigned to directly.
@end deftypevar

@deftypevar {char *} rl_terminal_name
The terminal type, used for initialization.
@end deftypevar

@deftypevar {char *} rl_readline_name
This variable is set to a unique name by each application using Readline.
The value allows conditional parsing of the inputrc file
(@pxref{Conditional Init Constructs}).
@end deftypevar

@deftypevar {FILE *} rl_instream
The stdio stream from which Readline reads input.
@end deftypevar

@deftypevar {FILE *} rl_outstream
The stdio stream to which Readline performs output.
@end deftypevar

@deftypevar {Function *} rl_startup_hook
If non-zero, this is the address of a function to call just
before @code{readline} prints the first prompt.
@end deftypevar

@deftypevar {Function *} rl_event_hook
If non-zero, this is the address of a function to call periodically
when readline is waiting for terminal input.
@end deftypevar

@node Readline Convenience Functions
@section Readline Convenience Functions

@menu
* Function Naming::	How to give a function you write a name.
* Keymaps::		Making keymaps.
* Binding Keys::	Changing Keymaps.
* Associating Function Names and Bindings::	Translate function names to
						key sequences.
* Allowing Undoing::	How to make your functions undoable.
* Redisplay::		Functions to control line display.
* Modifying Text::	Functions to modify @code{rl_line_buffer}.
* Utility Functions::	Generally useful functions and hooks.
@end menu

@node Function Naming
@subsection Naming a Function

The user can dynamically change the bindings of keys while using
Readline.  This is done by representing the function with a descriptive
name.  The user is able to type the descriptive name when referring to
the function.  Thus, in an init file, one might find

@example
Meta-Rubout:	backward-kill-word
@end example

This binds the keystroke @key{Meta-Rubout} to the function
@emph{descriptively} named @code{backward-kill-word}.  You, as the
programmer, should bind the functions you write to descriptive names as
well.  Readline provides a function for doing that:

@deftypefun int rl_add_defun (char *name, Function *function, int key)
Add @var{name} to the list of named functions.  Make @var{function} be
the function that gets called.  If @var{key} is not -1, then bind it to
@var{function} using @code{rl_bind_key ()}.
@end deftypefun

Using this function alone is sufficient for most applications.  It is
the recommended way to add a few functions to the default functions that
Readline has built in.  If you need to do something other
than adding a function to Readline, you may need to use the
underlying functions described below.

@node Keymaps
@subsection Selecting a Keymap

Key bindings take place on a @dfn{keymap}.  The keymap is the
association between the keys that the user types and the functions that
get run.  You can make your own keymaps, copy existing keymaps, and tell
Readline which keymap to use.

@deftypefun Keymap rl_make_bare_keymap ()
Returns a new, empty keymap.  The space for the keymap is allocated with
@code{malloc ()}; you should @code{free ()} it when you are done.
@end deftypefun

@deftypefun Keymap rl_copy_keymap (Keymap map)
Return a new keymap which is a copy of @var{map}.
@end deftypefun

@deftypefun Keymap rl_make_keymap ()
Return a new keymap with the printing characters bound to rl_insert,
the lowercase Meta characters bound to run their equivalents, and
the Meta digits bound to produce numeric arguments.
@end deftypefun

@deftypefun void rl_discard_keymap (Keymap keymap)
Free the storage associated with @var{keymap}.
@end deftypefun

Readline has several internal keymaps.  These functions allow you to
change which keymap is active.

@deftypefun Keymap rl_get_keymap ()
Returns the currently active keymap.
@end deftypefun

@deftypefun void rl_set_keymap (Keymap keymap)
Makes @var{keymap} the currently active keymap.
@end deftypefun

@deftypefun Keymap rl_get_keymap_by_name (char *name)
Return the keymap matching @var{name}.  @var{name} is one which would
be supplied in a @code{set keymap} inputrc line (@pxref{Readline Init File}).
@end deftypefun

@node Binding Keys
@subsection Binding Keys

You associate keys with functions through the keymap.  Readline has
several internal keymaps: @code{emacs_standard_keymap},
@code{emacs_meta_keymap}, @code{emacs_ctlx_keymap},
@code{vi_movement_keymap}, and @code{vi_insertion_keymap}.
@code{emacs_standard_keymap} is the default, and the examples in
this manual assume that.

These functions manage key bindings.

@deftypefun int rl_bind_key (int key, Function *function)
Binds @var{key} to @var{function} in the currently active keymap.
Returns non-zero in the case of an invalid @var{key}.
@end deftypefun

@deftypefun int rl_bind_key_in_map (int key, Function *function, Keymap map)
Bind @var{key} to @var{function} in @var{map}.  Returns non-zero in the case
of an invalid @var{key}.
@end deftypefun

@deftypefun int rl_unbind_key (int key)
Bind @var{key} to the null function in the currently active keymap.
Returns non-zero in case of error.
@end deftypefun

@deftypefun int rl_unbind_key_in_map (int key, Keymap map)
Bind @var{key} to the null function in @var{map}.
Returns non-zero in case of error.
@end deftypefun

@deftypefun int rl_generic_bind (int type, char *keyseq, char *data, Keymap map)
Bind the key sequence represented by the string @var{keyseq} to the arbitrary
pointer @var{data}.  @var{type} says what kind of data is pointed to by
@var{data}; this can be a function (@code{ISFUNC}), a macro
(@code{ISMACR}), or a keymap (@code{ISKMAP}).  This makes new keymaps as
necessary.  The initial keymap in which to do bindings is @var{map}.
@end deftypefun

@deftypefun int rl_parse_and_bind (char *line)
Parse @var{line} as if it had been read from the @code{inputrc} file and
perform any key bindings and variable assignments found
(@pxref{Readline Init File}).
@end deftypefun

@deftypefun int rl_read_init_file (char *filename)
Read keybindings and variable assignments from @var{filename}
(@pxref{Readline Init File}).
@end deftypefun

@node Associating Function Names and Bindings
@subsection Associating Function Names and Bindings

These functions allow you to find out what keys invoke named functions
and the functions invoked by a particular key sequence.

@deftypefun {Function *} rl_named_function (char *name)
Return the function with name @var{name}.
@end deftypefun

@deftypefun {Function *} rl_function_of_keyseq (char *keyseq, Keymap map, int *type)
Return the function invoked by @var{keyseq} in keymap @var{map}.
If @var{map} is NULL, the current keymap is used.  If @var{type} is
not NULL, the type of the object is returned in it (one of @code{ISFUNC},
@code{ISKMAP}, or @code{ISMACR}).
@end deftypefun

@deftypefun {char **} rl_invoking_keyseqs (Function *function)
Return an array of strings representing the key sequences used to
invoke @var{function} in the current keymap.
@end deftypefun

@deftypefun {char **} rl_invoking_keyseqs_in_map (Function *function, Keymap map)
Return an array of strings representing the key sequences used to
invoke @var{function} in the keymap @var{map}.
@end deftypefun

@deftypefun void rl_function_dumper (int readable)