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@comment %**start of header (This is for running Texinfo on a region.)
@setfilename rltech.info
@synindex fn vr
@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 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 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.
@end menu

@node Default Behaviour
@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 for @code{readline}
in ANSI C is

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

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 @code{gets ()} library
function:

@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 *
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);
@}
@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

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, etc.

@node Custom Functions
@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
@subsection The Function Type

For the sake of readabilty, we declare a new type of object, called
@dfn{Function}.  A @code{Function} is a C language 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;}

we have

@code{Function *func;}

@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:

@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
@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 {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 defun

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

@defun {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 defun

@node Binding Keys
@subsection Binding Keys

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

@defun {int 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 {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 defun

@defun {int 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 {int 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

@defun 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}; right now this can be a function (@code{ISFUNC}), a macro
(@code{ISMACR}), or a keymap (@code{ISKMAP}).  This makes new keymaps as
necessary.  The initial place to do bindings is in @var{map}.
@end defun

@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 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 (int count, int 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
@subsection Allowing Undoing

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 @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 should 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

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 @samp{M-c}, then typing @samp{M-c} would
change the case of the character under point.  Typing @samp{10 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. */
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;
@}
@end example

@node Custom Completers
@section Custom Completers

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
* How Completing Works::    The logic used to do completion.
* Completion Functions::    Functions provided by Readline.
* Completion Variables::    Variables which control completion.
* A Short Completion Example::    An example of writing completer subroutines.
@end menu

@node How Completing Works
@subsection How Completing Works

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:

@enumerate
@item
The user-interface function @code{rl_complete ()}.  This function is
called interactively with the same calling conventions as other
functions in readline intended for interactive use; i.e. @var{count},
and @code{invoking-key}.  It isolates the word to be completed and calls
@code{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.

@item
The internal function @code{completion_matches ()} uses your
@dfn{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 @code{rl_completion_entry_function}.

@item
The generator function is called repeatedly from
@code{completion_matches ()}, returning a string each time.  The
arguments to the generator function are @var{text} and @var{state}.
@var{text} is the partial word to be completed.  @var{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 @code{(char
*)NULL} this signals @code{completion_matches ()} that there are no more
possibilities left.

@end enumerate

@defun rl_complete (int ignore, int invoking_key)
Complete the word at or before point.  You have supplied the function
that does the initial simple matching selection algorithm (see
@code{completion_matches ()}).  The default is to do filename completion.
@end defun

Note that @code{rl_complete ()} has the identical calling conventions as
any other key-invokable function; this is because by default it is bound
to the @samp{TAB} key.

@defvar {Function *rl_completion_entry_function}
This is a pointer to the generator function for @code{completion_matches
()}.  If the value of @code{rl_completion_entry_function} is
@code{(Function *)NULL} then the default filename generator function is
used, namely @code{filename_entry_function ()}.
@end defvar

@node Completion Functions
@subsection Completion Functions

Here is the complete list of callable completion functions present in
Readline.

@defun rl_complete_internal (int what_to_do)
Complete the word at or before point.  @var{what_to_do} says what to do
with the completion.  A value of @samp{?} means list the possible
completions.  @samp{TAB} means do standard completion.  @samp{*} means
insert all of the possible completions.
@end defun

@defun rl_complete (int ignore, int invoking_key)
Complete the word at or before point.  You have supplied the function
that does the initial simple matching selection algorithm (see
@code{completion_matches ()}).  The default is to do filename
completion.  This just calls @code{rl_complete_internal ()} with an
argument of @samp{TAB}.
@end defun

@defun rl_possible_completions ()
List the possible completions.  See description of @code{rl_complete
()}.  This just calls @code{rl_complete_internal ()} with an argument of
@samp{?}.
@end defun

@defun {char **completion_matches} (char *text, char *(*entry_function) ())
Returns an array of @code{(char *)} which is a list of completions for
@var{text}.  If there are no completions, returns @code{(char **)NULL}.
The first entry in the returned array is the substitution for @var{text}.
The remaining entries are the possible completions.  The array is
terminated with a @code{NULL} pointer.

@var{entry_function} is a function of two args, and returns a
@code{(char *)}.  The first argument is @var{text}.  The second is a
state argument; it is zero on the first call, and non-zero on subsequent
calls.  It returns a @code{NULL}  pointer to the caller when there are
no more matches.
@end defun

@defun {char *filename_completion_function} (char *text, int state)
A generator function for filename completion in the general case.  Note
that completion in the Bash shell is a little different because of all
the pathnames that must be followed when looking up the completion for a
command.
@end defun

@defun {char *username_completion_function} (char *text, int state)
A completion generator for usernames.  @var{text} contains a partial
username preceded by a random character (usually @samp{~}).
@end defun

@node Completion Variables
@subsection Completion Variables

@defvar {Function *rl_completion_entry_function}
A pointer to the generator function for @code{completion_matches ()}.
@code{NULL} means to use @code{filename_entry_function ()}, the default
filename completer.
@end defvar

@defvar {Function *rl_attempted_completion_function}
A pointer to an alternative function to create matches.
The function is called with @var{text}, @var{start}, and @var{end}.
@var{start} and @var{end} are indices in @code{rl_line_buffer} saying
what the boundaries of @var{text} are.  If this function exists and
returns @code{NULL} then @code{rl_complete ()} will call the value of
@code{rl_completion_entry_function} to generate matches, otherwise the
array of strings returned will be used.
@end defvar

@defvar {int rl_completion_query_items}
Up to this many items will be displayed in response to a
possible-completions call.  After that, we ask the user if she is sure
she wants to see them all.  The default value is 100.
@end defvar

@defvar {char *rl_basic_word_break_characters}
The basic list of characters that signal a break between words for the
completer routine.  The contents of this variable is what breaks words
in the Bash shell, i.e. " \t\n\"\\'`@@$><=".
@end defvar

@defvar {char *rl_completer_word_break_characters}
The list of characters that signal a break between words for
@code{rl_complete_internal ()}.  The default list is the contents of
@code{rl_basic_word_break_characters}.
@end defvar

@defvar {char *rl_special_prefixes}
The list of characters that are word break characters, but should be
left in @var{text} when it is passed to the completion function.
Programs can use this to help determine what kind of completing to do.
@end defvar

@defvar {int rl_ignore_completion_duplicates}
If non-zero, then disallow duplicates in the matches.  Default is 1.
@end defvar

@defvar {int rl_filename_completion_desired}
Non-zero means that the results of the matches are to be treated as
filenames.  This is @emph{always} zero on entry, and can only be changed
within a completion entry generator function.
@end defvar

@defvar {Function *rl_ignore_some_completions_function}
This function, if defined, is called by the completer when real filename
completion is done, after all the matching names have been generated.  It
is passed a @code{NULL} terminated array of pointers to @code{(char *)}
known as @var{matches} in the code.  The 1st element (@code{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 @code{free()}'d.
@end defvar

@node A Short Completion Example
@subsection A Short Completion Example

Here is a small application demonstrating the use of the GNU Readline
library.  It is called @code{fileman}, and the source code resides in
@file{readline/examples/fileman.c}.  This sample application provides
completion of command names, line editing features, and access to the
history list.

@page
@smallexample
/* 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;
@page
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';
@}
@page
/* **************************************************************** */
/*                                                                  */
/*                  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);
@}
@page
/* **************************************************************** */
/*                                                                  */
/*                       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;
@{
  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);
@}
@end smallexample