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.
Many programs provide a command line interface, such as mail,
ftp, and 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
gets() or fgets ().
The function readline () prints a prompt and then reads and returns
a single line of text from the user. The line readline
returns is allocated with malloc (); you should free ()
the line when you are done with it. The declaration for readline
in ANSI C is
char *readline (char *prompt);
So, one might say
char *line = readline ("Enter a line: ");
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 readline encounters an EOF while reading the line, and the
line is empty at that point, then (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
C-p for example), you must call add_history () to save the
line away in a history list of such lines.
add_history (line);
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 gets () library
function, and has the advantage of no static buffer to overflow:
/* 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);
}
This function gives the user the default behaviour of TAB
completion: completion on file names. If you do not want Readline to
complete on filenames, you can change the binding of the TAB key
with rl_bind_key ().
int rl_bind_key (int key, int (*function)());
rl_bind_key () takes two arguments: key is the character that
you want to bind, and function is the address of the function to
call when key is pressed. Binding TAB to rl_insert ()
makes TAB insert itself.
rl_bind_key () returns non-zero if key is not a valid
ASCII character code (between 0 and 255).
Thus, to disable the default TAB behavior, the following suffices:
rl_bind_key ('\t', rl_insert);
This code should be executed once at the start of your program; you
might write a function called initialize_readline () which
performs this and other desired initializations, such as installing
custom completers (see section Custom Completers).
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.
For readabilty, we declare a new type of object, called
Function. A Function is a C function which
returns an int. The type declaration for Function is:
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 func which was a pointer to a function. Instead of the classic C declaration
int (*)()func;
we may write
Function *func;
Similarly, there are
typedef void VFunction (); typedef char *CPFunction (); and typedef char **CPPFunction ();
for functions returning no value, pointer to char, and
pointer to pointer to char, respectively.
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 foo looks like
foo (int count, int key)
where count is the numeric argument (or 1 if defaulted) and 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.
rl_line_buffer
(the point).
rl_line_buffer. When
rl_point is at the end of the line, rl_point and
rl_end are equal.
readline (), and should not be assigned to directly.
readline prints the first prompt.
rl_line_buffer.
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
Meta-Rubout: backward-kill-word
This binds the keystroke Meta-Rubout to the function
descriptively named 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:
rl_bind_key ().
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.
Key bindings take place on a 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.
malloc (); you should free () it when you are done.
Readline has several internal keymaps. These functions allow you to change which keymap is active.
set keymap inputrc line (see section Readline Init File).
You associate keys with functions through the keymap. Readline has
several internal keymaps: emacs_standard_keymap,
emacs_meta_keymap, emacs_ctlx_keymap,
vi_movement_keymap, and vi_insertion_keymap.
emacs_standard_keymap is the default, and the examples in
this manual assume that.
These functions manage key bindings.
ISFUNC), a macro
(ISMACR), or a keymap (ISKMAP). This makes new keymaps as
necessary. The initial keymap in which to do bindings is map.
inputrc file and
perform any key bindings and variable assignments found
(see section Readline Init File).
These functions allow you to find out what keys invoke named functions and the functions invoked by a particular key sequence.
ISFUNC,
ISKMAP, or ISMACR).
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 rl_insert_text () or 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 rl_begin_undo_group () and
rl_end_undo_group ().
The types of events that can be undone are:
enum undo_code { UNDO_DELETE, UNDO_INSERT, UNDO_BEGIN, UNDO_END };
Notice that UNDO_DELETE means to insert some text, and
UNDO_INSERT means to delete some text. That is, the undo code
tells undo what to undo, not how to undo it. UNDO_BEGIN and
UNDO_END are tags added by rl_begin_undo_group () and
rl_end_undo_group ().
rl_insert_text () and
rl_delete_text (), but could be the result of calls to
rl_add_undo ().
rl_begin_undo_group
(). There should be one call to rl_end_undo_group ()
for each call to rl_begin_undo_group ().
0 if there was
nothing to undo, non-zero if something was undone.
Finally, if you neither insert nor delete text, but directly modify the
existing text (e.g., change its case), call rl_modifying ()
once, just before you modify the text. You must supply the indices of
the text range that you are going to modify.
rl_line_buffer.
printf. The
resulting string is displayed in the echo area. The echo area
is also used to display numeric arguments and search strings.
vt100).
bell-style.
The following are implemented as macros, defined in chartypes.h.
Here is a function which changes lowercase characters to their uppercase equivalents, and uppercase characters to lowercase. If this function was bound to `M-c', then typing `M-c' would change the case of the character under point. Typing `M-1 0 M-c' would change the case of the following 10 characters, leaving the cursor on the last character changed.
/* 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);
}
Typically, a program that reads commands from the user has a way of disambiguating commands and data. If your program is one of these, then it can provide completion for commands, data, or both. The following sections describe how your program and Readline cooperate to provide this service.
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:
rl_complete (). This function is
called with the same arguments as other Readline
functions intended for interactive use: count and
invoking_key. It isolates the word to be completed and calls
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.
completion_matches () uses your
generator function to generate the list of possible matches, and
then returns the array of these matches. You should place the address
of your generator function in rl_completion_entry_function.
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. When the generator function returns
(char *)NULL this signals 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.
completion_matches ()). The default is to do filename completion.
completion_matches
(). If the value of rl_completion_entry_function is
(Function *)NULL then the default filename generator function,
filename_entry_function (), is used.
Here is the complete list of callable completion functions present in Readline.
completion_matches () and rl_completion_entry_function).
The default is to do filename
completion. This calls rl_complete_internal () with an
argument depending on invoking_key.
rl_complete
(). This calls rl_complete_internal () with an argument of
`?'.
rl_complete ().
This calls rl_complete_internal () with an argument of `*'.
(char *) which is a list of completions for
text. If there are no completions, returns (char **)NULL.
The first entry in the returned array is the substitution for text.
The remaining entries are the possible completions. The array is
terminated with a NULL pointer.
entry_func is a function of two args, and returns a
(char *). The first argument is text. The second is a
state argument; it is zero on the first call, and non-zero on subsequent
calls. entry_func returns a NULL pointer to the caller
when there are no more matches.
completion_matches ().
NULL means to use filename_entry_function (), the default
filename completer.
rl_line_buffer saying
what the boundaries of text are. If this function exists and
returns NULL, or if this variable is set to NULL, then
rl_complete () will call the value of
rl_completion_entry_function to generate matches, otherwise the
array of strings returned will be used.
" \t\n\"\\'`@$><=;|&{(".
rl_complete_internal (). The default list is the value of
rl_basic_word_break_characters.
rl_completer_word_break_chars. This is always non-zero
on entry, and can only be changed within a completion entry generator
function.
NULL terminated array of matches.
The first element (matches[0]) is the
maximal substring common to all matches. This function can
re-arrange the list of matches as required, but each element deleted
from the array must be freed.
rl_completer_word_break_characters are treated as any other character,
unless they also appear within this list.
Here is a small application demonstrating the use of the GNU Readline
library. It is called fileman, and the source code resides in
`examples/fileman.c'. This sample application provides
completion of command names, line editing features, and access to the
history list.
/* fileman.c -- A tiny application which demonstrates how to use the
GNU Readline library. This application interactively allows users
to manipulate files and their modes. */
#include <stdio.h>
#include <sys/types.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/errno.h>
#include <readline/readline.h>
#include <readline/history.h>
extern char *getwd ();
extern char *xmalloc ();
/* The names of functions that actually do the manipulation. */
int com_list (), com_view (), com_rename (), com_stat (), com_pwd ();
int com_delete (), com_help (), com_cd (), com_quit ();
/* A structure which contains information on the commands this program
can understand. */
typedef struct {
char *name; /* User printable name of the function. */
Function *func; /* Function to call to do the job. */
char *doc; /* Documentation for this function. */
} COMMAND;
COMMAND commands[] = {
{ "cd", com_cd, "Change to directory DIR" },
{ "delete", com_delete, "Delete FILE" },
{ "help", com_help, "Display this text" },
{ "?", com_help, "Synonym for `help'" },
{ "list", com_list, "List files in DIR" },
{ "ls", com_list, "Synonym for `list'" },
{ "pwd", com_pwd, "Print the current working directory" },
{ "quit", com_quit, "Quit using Fileman" },
{ "rename", com_rename, "Rename FILE to NEWNAME" },
{ "stat", com_stat, "Print out statistics on FILE" },
{ "view", com_view, "View the contents of FILE" },
{ (char *)NULL, (Function *)NULL, (char *)NULL }
};
/* Forward declarations. */
char *stripwhite ();
COMMAND *find_command ();
/* The name of this program, as taken from argv[0]. */
char *progname;
/* When non-zero, this global means the user is done using this program. */
int done;
char *
dupstr (s)
int s;
{
char *r;
r = xmalloc (strlen (s) + 1);
strcpy (r, s);
return (r);
}
main (argc, argv)
int argc;
char **argv;
{
char *line, *s;
progname = argv[0];
initialize_readline (); /* Bind our completer. */
/* Loop reading and executing lines until the user quits. */
for ( ; done == 0; )
{
line = readline ("FileMan: ");
if (!line)
break;
/* Remove leading and trailing whitespace from the line.
Then, if there is anything left, add it to the history list
and execute it. */
s = stripwhite (line);
if (*s)
{
add_history (s);
execute_line (s);
}
free (line);
}
exit (0);
}
/* Execute a command line. */
int
execute_line (line)
char *line;
{
register int i;
COMMAND *command;
char *word;
/* Isolate the command word. */
i = 0;
while (line[i] && whitespace (line[i]))
i++;
word = line + i;
while (line[i] && !whitespace (line[i]))
i++;
if (line[i])
line[i++] = '\0';
command = find_command (word);
if (!command)
{
fprintf (stderr, "%s: No such command for FileMan.\n", word);
return (-1);
}
/* Get argument to command, if any. */
while (whitespace (line[i]))
i++;
word = line + i;
/* Call the function. */
return ((*(command->func)) (word));
}
/* Look up NAME as the name of a command, and return a pointer to that
command. Return a NULL pointer if NAME isn't a command name. */
COMMAND *
find_command (name)
char *name;
{
register int i;
for (i = 0; commands[i].name; i++)
if (strcmp (name, commands[i].name) == 0)
return (&commands[i]);
return ((COMMAND *)NULL);
}
/* Strip whitespace from the start and end of STRING. Return a pointer
into STRING. */
char *
stripwhite (string)
char *string;
{
register char *s, *t;
for (s = string; whitespace (*s); s++)
;
if (*s == 0)
return (s);
t = s + strlen (s) - 1;
while (t > s && whitespace (*t))
t--;
*++t = '\0';
return s;
}
/* **************************************************************** */
/* */
/* Interface to Readline Completion */
/* */
/* **************************************************************** */
char *command_generator ();
char **fileman_completion ();
/* Tell the GNU Readline library how to complete. We want to try to complete
on command names if this is the first word in the line, or on filenames
if not. */
initialize_readline ()
{
/* Allow conditional parsing of the ~/.inputrc file. */
rl_readline_name = "FileMan";
/* Tell the completer that we want a crack first. */
rl_attempted_completion_function = (CPPFunction *)fileman_completion;
}
/* Attempt to complete on the contents of TEXT. START and END show the
region of TEXT that contains the word to complete. We can use the
entire line in case we want to do some simple parsing. Return the
array of matches, or NULL if there aren't any. */
char **
fileman_completion (text, start, end)
char *text;
int start, end;
{
char **matches;
matches = (char **)NULL;
/* If this word is at the start of the line, then it is a command
to complete. Otherwise it is the name of a file in the current
directory. */
if (start == 0)
matches = completion_matches (text, command_generator);
return (matches);
}
/* Generator function for command completion. STATE lets us know whether
to start from scratch; without any state (i.e. STATE == 0), then we
start at the top of the list. */
char *
command_generator (text, state)
char *text;
int state;
{
static int list_index, len;
char *name;
/* If this is a new word to complete, initialize now. This includes
saving the length of TEXT for efficiency, and initializing the index
variable to 0. */
if (!state)
{
list_index = 0;
len = strlen (text);
}
/* Return the next name which partially matches from the command list. */
while (name = commands[list_index].name)
{
list_index++;
if (strncmp (name, text, len) == 0)
return (dupstr(name));
}
/* If no names matched, then return NULL. */
return ((char *)NULL);
}
/* **************************************************************** */
/* */
/* FileMan Commands */
/* */
/* **************************************************************** */
/* String to pass to system (). This is for the LIST, VIEW and RENAME
commands. */
static char syscom[1024];
/* List the file(s) named in arg. */
com_list (arg)
char *arg;
{
if (!arg)
arg = "";
sprintf (syscom, "ls -FClg %s", arg);
return (system (syscom));
}
com_view (arg)
char *arg;
{
if (!valid_argument ("view", arg))
return 1;
sprintf (syscom, "more %s", arg);
return (system (syscom));
}
com_rename (arg)
char *arg;
{
too_dangerous ("rename");
return (1);
}
com_stat (arg)
char *arg;
{
struct stat finfo;
if (!valid_argument ("stat", arg))
return (1);
if (stat (arg, &finfo) == -1)
{
perror (arg);
return (1);
}
printf ("Statistics for `%s':\n", arg);
printf ("%s has %d link%s, and is %d byte%s in length.\n", arg,
finfo.st_nlink,
(finfo.st_nlink == 1) ? "" : "s",
finfo.st_size,
(finfo.st_size == 1) ? "" : "s");
printf ("Inode Last Change at: %s", ctime (&finfo.st_ctime));
printf (" Last access at: %s", ctime (&finfo.st_atime));
printf (" Last modified at: %s", ctime (&finfo.st_mtime));
return (0);
}
com_delete (arg)
char *arg;
{
too_dangerous ("delete");
return (1);
}
/* Print out help for ARG, or for all of the commands if ARG is
not present. */
com_help (arg)
char *arg;
{
register int i;
int printed = 0;
for (i = 0; commands[i].name; i++)
{
if (!*arg || (strcmp (arg, commands[i].name) == 0))
{
printf ("%s\t\t%s.\n", commands[i].name, commands[i].doc);
printed++;
}
}
if (!printed)
{
printf ("No commands match `%s'. Possibilties are:\n", arg);
for (i = 0; commands[i].name; i++)
{
/* Print in six columns. */
if (printed == 6)
{
printed = 0;
printf ("\n");
}
printf ("%s\t", commands[i].name);
printed++;
}
if (printed)
printf ("\n");
}
return (0);
}
/* Change to the directory ARG. */
com_cd (arg)
char *arg;
{
if (chdir (arg) == -1)
{
perror (arg);
return 1;
}
com_pwd ("");
return (0);
}
/* Print out the current working directory. */
com_pwd (ignore)
char *ignore;
{
char dir[1024], *s;
s = getwd (dir);
if (s == 0)
{
printf ("Error getting pwd: %s\n", dir);
return 1;
}
printf ("Current directory is %s\n", dir);
return 0;
}
/* The user wishes to quit using this program. Just set DONE non-zero. */
com_quit (arg)
char *arg;
{
done = 1;
return (0);
}
/* Function which tells you that you can't do this. */
too_dangerous (caller)
char *caller;
{
fprintf (stderr,
"%s: Too dangerous for me to distribute. Write it yourself.\n",
caller);
}
/* Return non-zero if ARG is a valid argument for CALLER, else print
an error message and return zero. */
int
valid_argument (caller, arg)
char *caller, *arg;
{
if (!arg || !*arg)
{
fprintf (stderr, "%s: Argument required.\n", caller);
return (0);
}
return (1);
}