path: root/readline/readline.texi

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* Readline: (readline).		The GNU Readline Library.
END-INFO-DIR-ENTRY
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@iftex
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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 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

@setchapternewpage odd
@titlepage
@sp 11
@center @titlefont{GNU Readline Library}
@sp 2
@center by Brian Fox
@sp 2
@center Version 1.0
@sp 2
@center February 1989

@comment   Include the Distribution inside the titlepage environment so
@c that headings are turned off. 

@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1989 Free Software Foundation, Inc.

@sp 2
This document describes the GNU Readline Library, a utility for aiding
in the consistency of user interface across discrete programs that need
to provide a command line interface.
@sp 2

Published by the Free Software Foundation @*
675 Massachusetts Avenue, @*
Cambridge, MA 02139 USA

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

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 titlepage

@node Top, , ,(DIR)
@chapter GNU Readline Library

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

@menu
* Command Line Editing::        GNU Readline User's Manual
* Readline Technical::	        GNU Readline Programmer's Manual
@end menu
@include inc-read.texi
@node Readline Technical, , Top, Top
@chapter Readline Programmer's Manual

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

@menu
* Default Behaviour::	Using the default behaviour of Readline.
* Custom Functions::	Adding your own functions to Readline.
* Custom Completers::	Supplanting or supplementing Readline's
			completion functions.
* Variable Index::	Index of externally tweakable variables.
@end menu

@node Default Behaviour, Custom Functions, Readline Technical, Readline Technical
@section Default Behaviour

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 ()}.

@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 which @code{readline ()}
returns is allocated with @code{malloc ()}; you should @code{free ()}
the line when you are done with it.  The declaration in ANSI C is

@example
@code{char *readline (char *@var{prompt});}
@end example
or, preferably,
@example
@code{#include <readline/readline.h>}
@end example

So, one might say
@example
@code{char *line = readline ("Enter a line: ");}
@end example
in order to read a line of text from the user.

The line which is returned has the final newline removed, so only the
text of the line remains.

If readline encounters an 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 was 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

If you use @code{add_history ()}, you should also
@code{#include <readline/history.h>}
For full details on the GNU History Library, see the associated manual.

It is polite to avoid saving empty lines on the history list, since
no one has a burning need to reuse a blank line.  Here is a function
which usefully replaces the standard @code{gets ()} library function:

@example
#include <readline/readline.h>
#include <readline/history.h>

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

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

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

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

  return (my_gets_line);
@}
@end example

The above code 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 ()}.

@findex rl_bind_key ()

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

@code{rl_bind_key ()} takes 2 arguments; @var{key} is the character that
you want to bind, and @var{function} is the address of the function to
run when @var{key} is pressed.  Binding @key{TAB} to @code{rl_insert ()}
makes @key{TAB} just insert itself.

@code{rl_bind_key ()} returns non-zero if @var{key} is not a valid
ASCII character code (between 0 and 255).

@example
@code{rl_bind_key ('\t', rl_insert);}
@end example

@node Custom Functions, Custom Completers, Default Behaviour, Readline Technical
@section Custom Functions

Readline provides a great 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 in 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 Naming::	How to give a function you write a name.
* Keymaps::		Making keymaps.
* Binding Keys::	Changing Keymaps.
* Function Writing::	Variables and calling conventions.
* Allowing Undoing::	How to make your functions undoable.
@end menu

@node The Function Type, Function Naming, Custom Functions, Custom Functions
For the sake of readabilty, we declare a new type of object, called
@dfn{Function}.  `Function' is a C language function which returns an
@code{int}.  The type declaration for `Function' is:

@code{typedef int Function ();}

The reason for declaring this new type is to make it easier to discuss
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;}

we have

@code{Function *func;}

@node Function Naming, Keymaps, The Function Type, Custom Functions
@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 @key{Meta-Rubout} to the function @emph{descriptively} named
@code{backward-kill-word}.  You, as a programmer, should bind the
functions you write to descriptive names as well.  Here is how to do
that.

@defun 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 defun

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 already.  If you need to do more or different
things than adding a function to Readline, you may need to use the
underlying functions described below.

@node Keymaps, Binding Keys, Function Naming, Custom Functions
@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.

@defun 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 defun

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

@defun 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 defun

@node Binding Keys, Function Writing, Keymaps, Custom Functions
@subsection Binding Keys

You associate keys with functions through the keymap.  Here are
the functions for doing that.

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

@defun 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 defun

@defun rl_unbind_key (int key)
Make @var{key} do nothing in the currently selected keymap.
Returns non-zero in case of error.
@end defun

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

@node Function Writing, Allowing Undoing, Binding Keys, Custom Functions
@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 gathered so far.

@defvar char *rl_line_buffer
This is the line gathered so far.  You are welcome to modify the
contents of this, but see Undoing, below.
@end defvar

@defvar int rl_point
The offset of the current cursor position in @var{rl_line_buffer}.
@end defvar

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

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

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

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, other
functions as a flag, and 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 a negative argument as well as a positive
argument.  At the very least, it should be aware that it can be passed a
negative argument.

@node Allowing Undoing, , Function Writing, Custom Functions
@subsection Allowing Undoing

Supporting the undo command is a painless thing to do, and makes your
function much more useful to the end user.  It is certainly easy to try
something if you know you can undo it.  I could use an undo function for
the stock market.

If your function simply inserts text once, or deletes text once, and it
calls @code{rl_insert_text ()} or @code{rl_delete_text ()} to do it, then
undoing is already done for you automatically, and you can safely skip
this section.

If you do multiple insertions or multiple deletions, or any combination
of these operations, you will want to group them together into one
operation.  This can be done with @code{rl_begin_undo_group ()} and 
@code{rl_end_undo_group ()}.

@defun rl_begin_undo_group ()
Begins saving undo information in a group construct.  The undo
information usually comes from calls to @code{rl_insert_text ()} and
@code{rl_delete_text ()}, but they could be direct calls to
@code{rl_add_undo ()}.
@end defun

@defun rl_end_undo_group ()
Closes the current undo group started with @code{rl_begin_undo_group
()}.  There should be exactly one call to @code{rl_end_undo_group ()}
for every call to @code{rl_begin_undo_group ()}.
@end defun

Finally, if you neither insert nor delete text, but directly modify the
existing text (e.g. change its case), you call @code{rl_modifying ()}
once, just before you modify the text.  You must supply the indices of
the text range that you are going to modify.

@defun rl_modifying (int start, int end)
Tell Readline to save the text between @var{start} and @var{end} as a
single undo unit.  It is assumed that subsequent to this call you will
modify that range of text in some way.
@end defun

@subsection An Example

Let us say that we are actually going to put an example here.

@node Custom Completers, Variable Index, Custom Functions, Readline Technical

Typically, a program that reads commands from the user has a way of
disambiguating between commands and data.  If your program is one of
these, then it can provide completion for either commands, or data, or
both commands and data.  The following sections describe how your
program and Readline cooperate to provide this service to end users.

@menu
@end menu

@node Variable Index, , Custom Completers, Readline Technical
@appendix Variable Index
@printindex vr
@contents

@bye