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@comment %**start of header (This is for running Texinfo on a region.)

@setfilename rltech.info

@comment %**end of header (This is for running Texinfo on a region.)

@setchapternewpage odd

@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, 1996, 1998, 1999 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

                                        functions.

* Readline Signal Handling::    How Readline behaves when it receives signals.

* 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.

Before declaring any functions that customize Readline's behavior, or

using any functionality Readline provides in other code, an

application writer should include the file @code{<readline/readline.h>}

in any file that uses Readline's features.  Since some of the definitions

in @code{readline.h} use the @code{stdio} library, the file

@code{<stdio.h>} should be included before @code{readline.h}.

@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}.  The

function @code{rl_extend_line_buffer} is available to increase

the memory allocated to @code{rl_line_buffer}.

@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 int rl_erase_empty_line

Setting this to a non-zero value causes Readline to completely erase

the current line, including any prompt, any time a newline is typed as

the only character on an otherwise-empty line.  The cursor is moved to

the beginning of the newly-blank line.

@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 int rl_already_prompted

If an application wishes to display the prompt itself, rather than have

Readline do it the first time @code{readline()} is called, it should set

this variable to a non-zero value after displaying the prompt.

The prompt must also be passed as the argument to @code{readline()} so

the redisplay functions can update the display properly.

The calling application is responsible for managing the value; Readline

never sets it.

@end deftypevar

@deftypevar {char *} rl_library_version

The version number of this revision of the library.

@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_pre_input_hook

If non-zero, this is the address of a function to call after

the first prompt has been printed and just before @code{readline}

starts reading input characters.

@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

@deftypevar {Function *} rl_getc_function

If non-zero, @code{readline} will call indirectly through this pointer

to get a character from the input stream.  By default, it is set to

@code{rl_getc}, the default @code{readline} character input function

(@pxref{Utility Functions}).

@end deftypevar

@deftypevar {VFunction *} rl_redisplay_function

If non-zero, @code{readline} will call indirectly through this pointer

to update the display with the current contents of the editing buffer.

By default, it is set to @code{rl_redisplay}, the default @code{readline}

redisplay function (@pxref{Redisplay}).

@end deftypevar

@deftypevar {Keymap} rl_executing_keymap

This variable is set to the keymap (@pxref{Keymaps}) in which the

currently executing readline function was found.

@end deftypevar

@deftypevar {Keymap} rl_binding_keymap

This variable is set to the keymap (@pxref{Keymaps}) in which the

last key binding occurred.

@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.

* Alternate Interface:: Using Readline in a `callback' fashion.

@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

@deftypefun {char *} rl_get_keymap_name (Keymap keymap)

Return the name matching @var{keymap}.  @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.

Since @code{readline} installs a set of default key bindings the first

time it is called, there is always the danger that a custom binding

installed before the first call to @code{readline} will be overridden.

An alternate mechanism is to install custom key bindings in an

initialization function assigned to the @code{rl_startup_hook} variable

(@pxref{Readline Variables}).

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_unbind_function_in_map (Function *function, Keymap map)

Unbind all keys that execute @var{function} in @var{map}.

@end deftypefun

@deftypefun int rl_unbind_command_in_map (char *command, Keymap map)

Unbind all keys that are bound to @var{command} in @var{map}.

@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)

Print the readline function names and the key sequences currently

bound to them to @code{rl_outstream}.  If @var{readable} is non-zero,

the list is formatted in such a way that it can be made part of an

@code{inputrc} file and re-read.

@end deftypefun

@deftypefun void rl_list_funmap_names ()

Print the names of all bindable Readline functions to @code{rl_outstream}.

@end deftypefun

@deftypefun {char **} rl_funmap_names ()

Return a NULL terminated array of known function names.  The array is

sorted.  The array itself is allocated, but not the strings inside.  You

should free () the array when you done, but not the pointrs.

@end deftypefun

@node Allowing Undoing

@subsection Allowing Undoing

Supporting the undo command is a painless thing, and makes your

functions much more useful.  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

uses @code{rl_insert_text ()} or @code{rl_delete_text ()} to do it, then

undoing is already done for you automatically.

If you do multiple insertions or multiple deletions, or any combination

of these operations, you should group them together into one operation.

This is done with @code{rl_begin_undo_group ()} and

@code{rl_end_undo_group ()}.

The types of events that can be undone are:

@example

enum undo_code @{ UNDO_DELETE, UNDO_INSERT, UNDO_BEGIN, UNDO_END @};

@end example

Notice that @code{UNDO_DELETE} means to insert some text, and

@code{UNDO_INSERT} means to delete some text.  That is, the undo code

tells undo what to undo, not how to undo it.  @code{UNDO_BEGIN} and

@code{UNDO_END} are tags added by @code{rl_begin_undo_group ()} and

@code{rl_end_undo_group ()}.

@deftypefun int 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 could be the result of calls to

@code{rl_add_undo ()}.

@end deftypefun

@deftypefun int rl_end_undo_group ()

Closes the current undo group started with @code{rl_begin_undo_group

()}.  There should be one call to @code{rl_end_undo_group ()}

for each call to @code{rl_begin_undo_group ()}.

@end deftypefun

@deftypefun void rl_add_undo (enum undo_code what, int start, int end, char *text)

Remember how to undo an event (according to @var{what}).  The affected

text runs from @var{start} to @var{end}, and encompasses @var{text}.

@end deftypefun

@deftypefun void free_undo_list ()

Free the existing undo list.

@end deftypefun

@deftypefun int rl_do_undo ()

Undo the first thing on the undo list.  Returns @code{0} if there was

nothing to undo, non-zero if something was undone.

@end deftypefun

Finally, if you neither insert nor delete text, but directly modify the

existing text (e.g., change its case), 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.

@deftypefun int 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 you will subsequently modify

that text.

@end deftypefun

@node Redisplay

@subsection Redisplay

@deftypefun void rl_redisplay ()

Change what's displayed on the screen to reflect the current contents

of @code{rl_line_buffer}.

@end deftypefun

@deftypefun int rl_forced_update_display ()

Force the line to be updated and redisplayed, whether or not

Readline thinks the screen display is correct.

@end deftypefun

@deftypefun int rl_on_new_line ()

Tell the update functions that we have moved onto a new (empty) line,

usually after ouputting a newline.

@end deftypefun

@deftypefun int rl_on_new_line_with_prompt ()

Tell the update functions that we have moved onto a new line, with

@var{rl_prompt} already displayed.

This could be used by applications that want to output the prompt string

themselves, but still need Readline to know the prompt string length for

redisplay.

It should be used after setting @var{rl_already_prompted}.

@end deftypefun

@deftypefun int rl_reset_line_state ()

Reset the display state to a clean state and redisplay the current line

starting on a new line.

@end deftypefun

@deftypefun int rl_message (va_alist)

The arguments are a string as would be supplied to @code{printf}.  The

resulting string is displayed in the @dfn{echo area}.  The echo area

is also used to display numeric arguments and search strings.

@end deftypefun

@deftypefun int rl_clear_message ()

Clear the message in the echo area.

@end deftypefun

@deftypefun void rl_save_prompt ()

Save the local Readline prompt display state in preparation for

displaying a new message in the message area with @code{rl_message}.

@end deftypefun

@deftypefun void rl_restore_prompt ()

Restore the local Readline prompt display state saved by the most

recent call to @code{rl_save_prompt}.

@end deftypefun

@node Modifying Text

@subsection Modifying Text

@deftypefun int rl_insert_text (char *text)

Insert @var{text} into the line at the current cursor position.

@end deftypefun

@deftypefun int rl_delete_text (int start, int end)

Delete the text between @var{start} and @var{end} in the current line.

@end deftypefun

@deftypefun {char *} rl_copy_text (int start, int end)

Return a copy of the text between @var{start} and @var{end} in

the current line.

@end deftypefun

@deftypefun int rl_kill_text (int start, int end)

Copy the text between @var{start} and @var{end} in the current line

to the kill ring, appending or prepending to the last kill if the

last command was a kill command.  The text is deleted.

If @var{start} is less than @var{end},

the text is appended, otherwise prepended.  If the last command was

not a kill, a new kill ring slot is used.

@end deftypefun

@node Utility Functions

@subsection Utility Functions

@deftypefun int rl_read_key ()

Return the next character available.  This handles input inserted into

the input stream via @var{pending input} (@pxref{Readline Variables})

and @code{rl_stuff_char ()}, macros, and characters read from the keyboard.

@end deftypefun

@deftypefun int rl_getc (FILE *)

Return the next character available from the keyboard.

@end deftypefun

@deftypefun int rl_stuff_char (int c)

Insert @var{c} into the Readline input stream.  It will be "read"

before Readline attempts to read characters from the terminal with

@code{rl_read_key ()}.

@end deftypefun

@deftypefun int rl_extend_line_buffer (int len)

Ensure that @code{rl_line_buffer} has enough space to hold @var{len}

characters, possibly reallocating it if necessary.

@end deftypefun

@deftypefun int rl_initialize ()

Initialize or re-initialize Readline's internal state.

@end deftypefun

@deftypefun int rl_reset_terminal (char *terminal_name)

Reinitialize Readline's idea of the terminal settings using

@var{terminal_name} as the terminal type (e.g., @code{vt100}).

If @var{terminal_name} is NULL, the value of the @code{TERM}

environment variable is used.

@end deftypefun

@deftypefun int alphabetic (int c)

Return 1 if @var{c} is an alphabetic character.

@end deftypefun

@deftypefun int numeric (int c)

Return 1 if @var{c} is a numeric character.

@end deftypefun

@deftypefun int ding ()

Ring the terminal bell, obeying the setting of @code{bell-style}.

@end deftypefun

@deftypefun void rl_display_match_list (char **matches, int len, int max)

A convenience function for displaying a list of strings in

columnar format on Readline's output stream.  @code{matches} is the list

of strings, in argv format, such as a list of completion matches.

@code{len} is the number of strings in @code{matches}, and @code{max}

is the length of the longest string in @code{matches}.  This function uses

the setting of @code{print-completions-horizontally} to select how the

matches are displayed (@pxref{Readline Init File Syntax}).

@end deftypefun

The following are implemented as macros, defined in @code{chartypes.h}.

@deftypefun int uppercase_p (int c)

Return 1 if @var{c} is an uppercase alphabetic character.

@end deftypefun

@deftypefun int lowercase_p (int c)

Return 1 if @var{c} is a lowercase alphabetic character.

@end deftypefun

@deftypefun int digit_p (int c)

Return 1 if @var{c} is a numeric character.

@end deftypefun

@deftypefun int to_upper (int c)

If @var{c} is a lowercase alphabetic character, return the corresponding

uppercase character.

@end deftypefun

@deftypefun int to_lower (int c)

If @var{c} is an uppercase alphabetic character, return the corresponding

lowercase character.

@end deftypefun

@deftypefun int digit_value (int c)

If @var{c} is a number, return the value it represents.

@end deftypefun

@node Alternate Interface

@subsection Alternate Interface

An alternate interface is available to plain @code{readline()}.  Some

applications need to interleave keyboard I/O with file, device, or

window system I/O, typically by using a main loop to @code{select()}

on various file descriptors.  To accomodate this need, readline can

also be invoked as a `callback' function from an event loop.  There

are functions available to make this easy.

@deftypefun void rl_callback_handler_install (char *prompt, Vfunction *lhandler)

Set up the terminal for readline I/O and display the initial

expanded value of @var{prompt}.  Save the value of @var{lhandler} to

use as a callback when a complete line of input has been entered.

@end deftypefun

@deftypefun void rl_callback_read_char ()

Whenever an application determines that keyboard input is available, it

should call @code{rl_callback_read_char()}, which will read the next

character from the current input source.  If that character completes the

line, @code{rl_callback_read_char} will invoke the @var{lhandler}

function saved by @code{rl_callback_handler_install} to process the

line.  @code{EOF} is  indicated by calling @var{lhandler} with a

@code{NULL} line.

@end deftypefun

@deftypefun void rl_callback_handler_remove ()

Restore the terminal to its initial state and remove the line handler.

This may be called from within a callback as well as independently.

@end deftypefun

@subsection An Example

Here is a function which changes lowercase characters to their uppercase

equivalents, and uppercase characters to lowercase.  If

this function was bound to @samp{M-c}, then typing @samp{M-c} would

change the case of the character under point.  Typing @samp{M-1 0 M-c}

would change the case of the following 10 characters, leaving the cursor on

the last character changed.

@example

/* Invert the case of the COUNT following characters. */

int

invert_case_line (count, key)

     int count, key;

@{

  register int start, end, i;

  start = rl_point;

  if (rl_point >= rl_end)

    return (0);

  if (count < 0)

    @{

      direction = -1;

      count = -count;

    @}

  else

    direction = 1;

  /* Find the end of the range to modify. */

  end = start + (count * direction);

  /* Force it to be within range. */

  if (end > rl_end)

    end = rl_end;

  else if (end < 0)

    end = 0;

  if (start == end)

    return (0);

  if (start > end)

    @{

      int temp = start;

      start = end;

      end = temp;

    @}

  /* Tell readline that we are modifying the line, so it will save

     the undo information. */

  rl_modifying (start, end);

  for (i = start; i != end; i++)

    @{

      if (uppercase_p (rl_line_buffer[i]))

        rl_line_buffer[i] = to_lower (rl_line_buffer[i]);

      else if (lowercase_p (rl_line_buffer[i]))

        rl_line_buffer[i] = to_upper (rl_line_buffer[i]);

    @}

  /* Move point to on top of the last character changed. */

  rl_point = (direction == 1) ? end - 1 : start;

  return (0);

@}

@end example

@node Readline Signal Handling

@section Readline Signal Handling

Signals are asynchronous events sent to a process by the Unix kernel,

sometimes on behalf of another process.  They are intended to indicate

exceptional events, like a user pressing the interrupt key on his

terminal, or a network connection being broken.  There is a class of

signals that can be sent to the process currently reading input from

the keyboard.  Since Readline changes the terminal attributes when it

is called, it needs to perform special processing when a signal is

received to restore the terminal to a sane state, or provide application

writers with functions to do so manually.

Readline contains an internal signal handler that is installed for a

number of signals (@code{SIGINT}, @code{SIGQUIT}, @code{SIGTERM},

@code{SIGALRM}, @code{SIGTSTP}, @code{SIGTTIN}, and @code{SIGTTOU}).

When one of these signals is received, the signal handler

will reset the terminal attributes to those that were in effect before

@code{readline ()} was called, reset the signal handling to what it was

before @code{readline ()} was called, and resend the signal to the calling

application.

If and when the calling application's signal handler returns, Readline

will reinitialize the terminal and continue to accept input.

When a @code{SIGINT} is received, the Readline signal handler performs

some additional work, which will cause any partially-entered line to be

aborted (see the description of @code{rl_free_line_state ()}).

There is an additional Readline signal handler, for @code{SIGWINCH}, which

the kernel sends to a process whenever the terminal's size changes (for

example, if a user resizes an @code{xterm}).  The Readline @code{SIGWINCH}

handler updates Readline's internal screen size state, and then calls any

@code{SIGWINCH} signal handler the calling application has installed.

Readline calls the application's @code{SIGWINCH} signal handler without

resetting the terminal to its original state.  If the application's signal

handler does more than update its idea of the terminal size and return (for

example, a @code{longjmp} back to a main processing loop), it @emph{must}

call @code{rl_cleanup_after_signal ()} (described below), to restore the

terminal state.

Readline provides two variables that allow application writers to

control whether or not it will catch certain signals and act on them

when they are received.  It is important that applications change the

values of these variables only when calling @code{readline ()}, not in

a signal handler, so Readline's internal signal state is not corrupted.

@deftypevar int rl_catch_signals