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.
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 ()
.
The function readline
prints a prompt and then reads and returns
a single line of text from the user. The line which 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 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 (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
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 polite to avoid saving empty lines on the history list, since it
is rare than someone has a burning need to reuse a blank line. Here is
a function which usefully replaces the standard gets ()
library
function:
/* 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 * do_gets () { /* If the buffer has already been allocated, return the memory to the free pool. */ if (line_read != (char *)NULL) { 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); }
The above code 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 2 arguments; key is the character that
you want to bind, and function is the address of the function to
run when key is pressed. Binding TAB to rl_insert ()
makes TAB just insert itself.
rl_bind_key ()
returns non-zero if key is not a valid
ASCII character code (between 0 and 255).
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, etc.
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.
For the sake of readabilty, we declare a new type of object, called
Function. A Function
is a C language 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 have
Function *func;
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 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.
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.
You associate keys with functions through the keymap. Here are functions for doing that.
ISFUNC
), a macro
(ISMACR
), or a keymap (ISKMAP
). This makes new keymaps as
necessary. The initial place to do bindings is in map.
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.
rl_line_buffer
. When
rl_point
is at the end of the line, then rl_point
and
rl_end
are equal.
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, 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.
Supporting the undo command is a painless thing to do, and makes your functions 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 rl_insert_text ()
or 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 should group them together into one operation.
This can be done with rl_begin_undo_group ()
and
rl_end_undo_group ()
.
rl_insert_text ()
and
rl_delete_text ()
, but they could be direct calls to
rl_add_undo ()
.
rl_begin_undo_group
()
. There should be exactly one call to rl_end_undo_group ()
for every call to rl_begin_undo_group ()
.
Finally, if you neither insert nor delete text, but directly modify the
existing text (e.g. change its case), you 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.
Here is a function which changes lowercase characters to the uppercase equivalents, and uppercase characters to the lowercase equivalents. If this function was bound to `M-c', then typing `M-c' would change the case of the character under point. Typing `10 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. */ invert_case_line (count, key) int count, key; { register int start, end; start = rl_point; 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 = -1; if (start > end) { int temp = start; start = end; end = temp; } if (start == end) return; /* Tell readline that we are modifying the line, so save the undo information. */ rl_modifying (start, end); for (; start != end; start += direction) { if (uppercase_p (rl_line_buffer[start])) rl_line_buffer[start] = to_lower (rl_line_buffer[start]); else if (lowercase_p (rl_line_buffer[start])) rl_line_buffer[start] = to_upper (rl_line_buffer[start]); } /* Move point to on top of the last character changed. */ rl_point = end - direction; }
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 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.
In order to complete some text, the full list of possible completions must be available. That is to say, it is not possible to accurately expand a partial word without knowing what all of the possible words that make sense in that context are. The GNU Readline library provides the user interface to completion, and additionally, 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 those functions must do, and provides an example function.
There are three major functions used to perform completion:
rl_complete ()
. This function is
called interactively with the same calling conventions as other
functions in readline intended for interactive use; i.e. 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 or actually performs the
completion, depending on which behaviour 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, 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.
completion_matches ()
). The default is to do filename completion.
Note that rl_complete ()
has the identical calling conventions as
any other key-invokable function; this is because by default it is bound
to the `TAB' key.
completion_matches
()
. If the value of rl_completion_entry_function
is
(Function *)NULL
then the default filename generator function is
used, namely filename_entry_function ()
.
Here is the complete list of callable completion functions present in Readline.
completion_matches ()
). The default is to do filename
completion. This just calls rl_complete_internal ()
with an
argument of `TAB'.
rl_complete
()
. This just 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_function 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. It 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
then rl_complete ()
will call the value of
rl_completion_entry_function
to generate matches, otherwise the
array of strings returned will be used.
rl_complete_internal ()
. The default list is the contents of
rl_basic_word_break_characters
.
NULL
terminated array of (char *)
known as
matches in the code. The 1st element (matches[0]
) is the
maximal substring that is common to all matches. This function can
re-arrange the list of matches as required, but each deleted element of
the array must be free()
'd.
Here is a small application demonstrating the use of the GNU Readline
library. It is called fileman
, and the source code resides in
`readline/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 <readline/readline.h> #include <readline/history.h> #include <sys/types.h> #include <sys/file.h> #include <sys/stat.h> #include <sys/errno.h> /* 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 } }; /* 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 = 0; main (argc, argv) int argc; char **argv; { progname = argv[0]; initialize_readline (); /* Bind our completer. */ /* Loop reading and executing lines until the user quits. */ while (!done) { char *line; line = readline ("FileMan: "); if (!line) { done = 1; /* Encountered EOF at top level. */ } else { /* Remove leading and trailing whitespace from the line. Then, if there is anything left, add it to the history list and execute it. */ stripwhite (line); if (*line) { add_history (line); execute_line (line); } } if (line) free (line); } exit (0); } /* Execute a command line. */ execute_line (line) char *line; { register int i; COMMAND *find_command (), *command; char *word; /* Isolate the command word. */ i = 0; while (line[i] && !whitespace (line[i])) i++; word = line; if (line[i]) line[i++] = '\0'; command = find_command (word); if (!command) { fprintf (stderr, "%s: No such command for FileMan.\n", word); return; } /* Get argument to command, if any. */ while (whitespace (line[i])) i++; word = line + i; /* Call the function. */ (*(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. */ stripwhite (string) char *string; { register int i = 0; while (whitespace (string[i])) i++; if (i) strcpy (string, string + i); i = strlen (string) - 1; while (i > 0 && whitespace (string[i])) i--; string[++i] = '\0'; } /* **************************************************************** */ /* */ /* Interface to Readline 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 () { char **fileman_completion (); /* Allow conditional parsing of the ~/.inputrc file. */ rl_readline_name = "FileMan"; /* Tell the completer that we want a crack first. */ rl_attempted_completion_function = (Function *)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; char *command_generator (); 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 (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); system (syscom); } com_view (arg) char *arg; { if (!valid_argument ("view", arg)) return; sprintf (syscom, "cat %s | more", arg); system (syscom); } com_rename (arg) char *arg; { too_dangerous ("rename"); } com_stat (arg) char *arg; { struct stat finfo; if (!valid_argument ("stat", arg)) return; if (stat (arg, &finfo) == -1) { perror (arg); return; } printf ("Statistics for `%s':\n", arg); printf ("%s has %d link%s, and is %d bytes in length.\n", arg, finfo.st_nlink, (finfo.st_nlink == 1) ? "" : "s", finfo.st_size); printf (" Created on: %s", ctime (&finfo.st_ctime)); printf (" Last access at: %s", ctime (&finfo.st_atime)); printf ("Last modified at: %s", ctime (&finfo.st_mtime)); } com_delete (arg) char *arg; { too_dangerous ("delete"); } /* 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"); } } /* Change to the directory ARG. */ com_cd (arg) char *arg; { if (chdir (arg) == -1) perror (arg); com_pwd (""); } /* Print out the current working directory. */ com_pwd (ignore) char *ignore; { char dir[1024]; (void) getwd (dir); printf ("Current directory is %s\n", dir); } /* The user wishes to quit using this program. Just set DONE non-zero. */ com_quit (arg) char *arg; { done = 1; } /* 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); }
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