Provided by: libtecla-dev_1.6.3-3.1build1_amd64 bug

NAME

       gl_get_line, new_GetLine, del_GetLine, gl_customize_completion, gl_change_terminal, gl_configure_getline,
       gl_load_history, gl_save_history, gl_group_history, gl_show_history, gl_watch_fd,  gl_inactivity_timeout,
       gl_terminal_size,     gl_set_term_size,     gl_resize_history,     gl_limit_history,    gl_clear_history,
       gl_toggle_history,  gl_lookup_history,  gl_state_of_history,   gl_range_of_history,   gl_size_of_history,
       gl_echo_mode,   gl_replace_prompt,  gl_prompt_style,  gl_ignore_signal,  gl_trap_signal,  gl_last_signal,
       gl_completion_action,    gl_display_text,    gl_return_status,    gl_error_message,     gl_catch_blocked,
       gl_list_signals,     gl_bind_keyseq,    gl_erase_terminal,    gl_automatic_history,    gl_append_history,
       gl_query_char, gl_read_char - allow the user to compose an input line

SYNOPSIS

       #include <stdio.h>
       #include <libtecla.h>

       GetLine *new_GetLine(size_t linelen, size_t histlen);

       GetLine *del_GetLine(GetLine *gl);

       char *gl_get_line(GetLine *gl, const char *prompt,
                         const char *start_line, int start_pos);

       int gl_query_char(GetLine *gl, const char *prompt,
                         char defchar);

       int gl_read_char(GetLine *gl);

       int gl_customize_completion(GetLine *gl, void *data,
                                   CplMatchFn *match_fn);

       int gl_change_terminal(GetLine *gl, FILE *input_fp,
                              FILE *output_fp, const char *term);

       int gl_configure_getline(GetLine *gl,
                                const char *app_string,
                                const char *app_file,
                                const char *user_file);

       int gl_bind_keyseq(GetLine *gl, GlKeyOrigin origin,
                          const char *keyseq, const char *action);

       int gl_save_history(GetLine *gl, const char *filename,
                           const char *comment, int max_lines);

       int gl_load_history(GetLine *gl, const char *filename,
                           const char *comment);

       int gl_watch_fd(GetLine *gl, int fd, GlFdEvent event,
                       GlFdEventFn *callback, void *data);

       int gl_inactivity_timeout(GetLine *gl, GlTimeoutFn *callback,
                          void *data, unsigned long sec,
                          unsigned long nsec);

       int gl_group_history(GetLine *gl, unsigned stream);

       int gl_show_history(GetLine *gl, FILE *fp,
                           const char *fmt, int all_groups,
                           int max_lines);

       int gl_resize_history(GetLine *gl, size_t bufsize);

       void gl_limit_history(GetLine *gl, int max_lines);

       void gl_clear_history(GetLine *gl, int all_groups);

       void gl_toggle_history(GetLine *gl, int enable);

       GlTerminalSize gl_terminal_size(GetLine *gl,
                                       int def_ncolumn,
                                       int def_nline);

       int gl_set_term_size(GetLine *gl, int ncolumn, int nline);

       int gl_lookup_history(GetLine *gl, unsigned long id,
                             GlHistoryLine *hline);

       void gl_state_of_history(GetLine *gl,
                                GlHistoryState *state);

       void gl_range_of_history(GetLine *gl,
                                GlHistoryRange *range);

       void gl_size_of_history(GetLine *gl, GlHistorySize *size);

       void gl_echo_mode(GetLine *gl, int enable);

       void gl_replace_prompt(GetLine *gl, const char *prompt);

       void gl_prompt_style(GetLine *gl, GlPromptStyle style);

       int gl_ignore_signal(GetLine *gl, int signo);

       int gl_trap_signal(GetLine *gl, int signo, unsigned flags,
                          GlAfterSignal after, int errno_value);

       int gl_last_signal(GetLine *gl);

       int gl_completion_action(GetLine *gl,
                                void *data, CplMatchFn *match_fn,
                                int list_only, const char *name,
                                const char *keyseq);

       int gl_register_action(GetLine *gl, void *data,
                              GlActionFn *fn, const char *name,
                              const char *keyseq);

       int gl_display_text(GetLine *gl, int indentation,
                           const char *prefix,
                           const char *suffix, int fill_char,
                           int def_width, int start,
                           const char *string);

       GlReturnStatus gl_return_status(GetLine *gl);

       const char *gl_error_message(GetLine *gl, char *buff,
                                    size_t n);

       void gl_catch_blocked(GetLine *gl);

       int gl_list_signals(GetLine *gl, sigset_t *set);

       int gl_append_history(GetLine *gl, const char *line);

       int gl_automatic_history(GetLine *gl, int enable);

DESCRIPTION

       The gl_get_line() function is part of the tecla library (see the libtecla(3) man page). If  the  user  is
       typing  at  a  terminal,  each  call prompts them for an line of input, then provides interactive editing
       facilities, similar to those of the unix tcsh shell. In  addition  to  simple  command-line  editing,  it
       supports  recall of previously entered command lines, TAB completion of file names, and in-line wild-card
       expansion of filenames. Documentation of both the user-level command-line editing features and  all  user
       configuration  options,  can  be  found  in  the  tecla(7)  man  page. This man page concerns itself with
       documentation for programmers interested in using this library in their application.

AN EXAMPLE

       The following shows a complete example of how to use the gl_get_line() function to  get  input  from  the
       user:

         #include <stdio.h>
         #include <locale.h>
         #include <libtecla.h>

         int main(int argc, char *argv[])
         {
           char *line;    /* The line that the user typed */
           GetLine *gl;   /* The gl_get_line() resource object */

           setlocale(LC_CTYPE, ""); /* Adopt the user's choice */
                                    /* of character set. */

           gl = new_GetLine(1024, 2048);
           if(!gl)
             return 1;

           while((line=gl_get_line(gl, "$ ", NULL, -1)) != NULL &&
                  strcmp(line, "exit\n") != 0)
             printf("You typed: %s\n", line);

           gl = del_GetLine(gl);
           return 0;
         }

       In  the  example,  first  the  resources  needed  by  the  gl_get_line()  function are created by calling
       new_GetLine(). This allocates the  memory  used  in  subsequent  calls  to  the  gl_get_line()  function,
       including the history buffer for recording previously entered lines. Then one or more lines are read from
       the user, until either an error occurs, or the user types exit. Then  finally  the  resources  that  were
       allocated by new_GetLine(), are returned to the system by calling del_GetLine(). Note the use of the NULL
       return value of del_GetLine() to make gl NULL. This is a safety precaution. If the  program  subsequently
       attempts  to  pass  gl  to  gl_get_line(),  said  function will complain, and return an error, instead of
       attempting to use the deleted resource object.

THE FUNCTIONS USED IN THE EXAMPLE

       The descriptions of the functions used in the example are as follows:

         GetLine *new_GetLine(size_t linelen, size_t histlen)

       This function creates the resources used by the gl_get_line() function and returns an opaque  pointer  to
       the  object  that  contains  them.   The  maximum  length  of  an input line is specified via the linelen
       argument, and the number of bytes to allocate for storing history lines is set by the  histlen  argument.
       History  lines  are  stored  back-to-back  in a single buffer of this size. Note that this means that the
       number of history lines that can be stored at any given time, depends on the lengths  of  the  individual
       lines.   If  you  want  to  place  an  upper  limit  on  the  number of lines that can be stored, see the
       gl_limit_history() function described later. If you don't want history at all, specify histlen  as  zero,
       and no history buffer will be allocated.

       On error, a message is printed to stderr and NULL is returned.

         GetLine *del_GetLine(GetLine *gl)

       This  function  deletes  the  resources that were returned by a previous call to new_GetLine(). It always
       returns NULL (ie a deleted object). It does nothing if the gl argument is NULL.

         char *gl_get_line(GetLine *gl, const char *prompt,
                          const char *start_line, int start_pos);

       The gl_get_line() function can be called any number of times to read input from the user. The gl argument
       must have been previously returned by a call to new_GetLine(). The prompt argument should be a normal NUL
       terminated string, specifying the prompt to present the user  with.  By  default  prompts  are  displayed
       literally, but if enabled with the gl_prompt_style() function (see later), prompts can contain directives
       to do underlining, switch to and from bold fonts, or turn highlighting on and off.

       If you want to specify the initial contents of the line, for the user to edit, pass  the  desired  string
       via  the  start_line  argument. You can then specify which character of this line the cursor is initially
       positioned over, using the start_pos argument. This should be -1 if you want the  cursor  to  follow  the
       last  character  of the start line. If you don't want to preload the line in this manner, send start_line
       as NULL, and set start_pos to -1. Note that the line pointer returned by one call to gl_get_line() can be
       passed back to the next call to gl_get_line() via the start_line. This allows the application to take the
       last entered line, and if it contains an error, to then present it back to the user for re-editing,  with
       the cursor initially positioned where the error was encountered.

       The  gl_get_line() function returns a pointer to the line entered by the user, or NULL on error or at the
       end of the input. The returned pointer is part of the specified gl resource object, and thus  should  not
       be  free'd by the caller, or assumed to be unchanging from one call to the next. When reading from a user
       at a terminal, there will always be a newline character at the end of the returned line.   When  standard
       input  is  being taken from a pipe or a file, there will similarly be a newline unless the input line was
       too long to store in the internal buffer. In the latter case you should call gl_get_line() again to  read
       the rest of the line. Note that this behavior makes gl_get_line() similar to fgets().  In fact when stdin
       isn't connected to a terminal,gl_get_line() just calls fgets().

THE RETURN STATUS OF GL_GET_LINE

       As described above, the gl_get_line() function has two possible return values; a pointer to the completed
       input  line,  or  NULL.  Extra information about what caused gl_get_line() to return is available both by
       inspecting errno, and by calling the gl_return_status() function.

         GlReturnStatus gl_return_status(GetLine *gl);

       The following are the possible enumerated values that this function returns.

         GLR_NEWLINE     -  The last call to gl_get_line()
                            successfully returned a completed
                            input line.

         GLR_BLOCKED     -  gl_get_line() was in non-blocking
                            server mode, and returned early to
                            avoid blocking the process while
                            waiting for terminal I/O. The
                            gl_pending_io() function can be
                            used to see what type of I/O
                            gl_get_line() was waiting for.
                            (see the gl_io_mode(3) man page
                            for details).

         GLR_SIGNAL      -  A signal was caught by
                            gl_get_line() that had an
                            after-signal disposition of
                            GLS_ABORT (See gl_trap_signal()).

         GLR_TIMEOUT     -  The inactivity timer expired while
                            gl_get_line() was waiting for
                            input, and the timeout callback
                            function returned GLTO_ABORT.
                            See gl_inactivity_timeout() for
                            information about timeouts.

         GLR_FDABORT     -  An application I/O callack returned
                            GLFD_ABORT (see gl_watch_fd()).

         GLR_EOF         -  End of file reached. This can happen
                            when input is coming from a file or a
                            pipe, instead of the terminal. It also
                            occurs if the user invokes the
                            list-or-eof or del-char-or-list-or-eof
                            actions at the start of a new line.

         GLR_ERROR       -  An unexpected error caused
                            gl_get_line() to abort (consult
                            errno and/or
                            gl_error_message() for details.

       When gl_return_status() returns GLR_ERROR, and the value  of  errno  isn't  sufficient  to  explain  what
       happened,  you  can  use  the gl_error_message() function to request a description of the last error that
       occurred.

         const char *gl_error_message(GetLine *gl, char *buff,
                                      size_t n);

       The return value is a pointer to the message that occurred. If the buff argument is NULL, this will be  a
       pointer  to  a  buffer  within  gl,  who's  value  will  probably change on the next call to any function
       associated with gl_get_line(). Otherwise, if a non-NULL buff argument is  provided,  the  error  message,
       including  a  '\0' terminator, will be written within the first n elements of this buffer, and the return
       value will be a pointer to the first element of this buffer. If the message won't  fit  in  the  provided
       buffer, it will be truncated to fit.

OPTIONAL PROMPT FORMATTING

       Whereas  by  default  the  prompt  string  that  you  specify is displayed literally, without any special
       interpretation of the characters within it, the gl_prompt_style() function can be used to enable optional
       formatting directives within the prompt.

         void gl_prompt_style(GetLine *gl, GlPromptStyle style);

       The style argument, which specifies the formatting style, can take any of the following values:

         GL_FORMAT_PROMPT   -  In this style, the formatting
                               directives described below, when
                               included in prompt strings, are
                               interpreted as follows:

                                 %B  -  Display subsequent
                                        characters with a bold
                                        font.
                                 %b  -  Stop displaying characters
                                        with the bold font.
                                 %F  -  Make subsequent characters
                                        flash.
                                 %f  -  Turn off flashing
                                        characters.
                                 %U  -  Underline subsequent
                                        characters.
                                 %u  -  Stop underlining
                                        characters.
                                 %P  -  Switch to a pale (half
                                        brightness) font.
                                 %p  -  Stop using the pale font.
                                 %S  -  Highlight subsequent
                                        characters (also known as
                                        standout mode).
                                 %s  -  Stop highlighting
                                        characters.
                                 %V  -  Turn on reverse video.
                                 %v  -  Turn off reverse video.
                                 %%  -  Display a single %
                                        character.

                               For example, in this mode, a prompt
                               string like "%UOK%u$ " would
                               display the prompt "OK$ ",
                               but with the OK part
                               underlined.

                               Note that although a pair of
                               characters that starts with a %
                               character, but doesn't match any of
                               the above directives is displayed
                               literally, if a new directive is
                               subsequently introduced which does
                               match, the displayed prompt will
                               change, so it is better to always
                               use %% to display a literal %.

                               Also note that not all terminals
                               support all of these text
                               attributes, and that some substitute
                               a different attribute for missing
                               ones.

         GL_LITERAL_PROMPT  -  In this style, the prompt string is
                               printed literally. This is the
                               default style.

ALTERNATE CONFIGURATION SOURCES

       As  mentioned  above, by default users have the option of configuring the behavior of gl_get_line() via a
       configuration file called .teclarc in their home directories. The fact that all applications  share  this
       same configuration file is both an advantage and a disadvantage.  In most cases it is an advantage, since
       it encourages uniformity, and frees the user from having to configure each  application  separately.   In
       some applications, however, this single means of configuration is a problem. This is particularly true of
       embedded software, where  there's  no  filesystem  to  read  a  configuration  file  from,  and  also  in
       applications  where  a  radically  different choice of keybindings is needed to emulate a legacy keyboard
       interface.  To cater for such cases, the following function  allows  the  application  to  control  where
       configuration information is read from.

         int gl_configure_getline(GetLine *gl,
                                  const char *app_string,
                                  const char *app_file,
                                  const char *user_file);

       It  allows  the  configuration  commands that would normally be read from a user's ~/.teclarc file, to be
       read from any or none of, a string, an application specific configuration file,  and/or  a  user-specific
       configuration  file.  If  this  function  is  called  before the first call to gl_get_line(), the default
       behavior of reading ~/.teclarc on the first call to gl_get_line() is disabled, so all configuration  must
       be achieved using the configuration sources specified with this function.

       If  app_string != NULL, then it is interpreted as a string containing one or more configuration commands,
       separated from each other in the string by embedded newline characters. If app_file != NULL  then  it  is
       interpreted as the full pathname of an application-specific configuration file. If user_file != NULL then
       it is interpreted as the full pathname of a user-specific configuration file,  such  as  ~/.teclarc.  For
       example, in the following call,

         gl_configure_getline(gl, "edit-mode vi \n nobeep",
                                  "/usr/share/myapp/teclarc",
                                  "~/.teclarc");

       the  app_string  argument causes the calling application to start in vi edit-mode, instead of the default
       emacs mode, and turns off the use of the terminal bell by the library. It then attempts to  read  system-
       wide  configuration  commands  from  an optional file called /usr/share/myapp/teclarc, then finally reads
       user-specific configuration commands from an optional .teclarc file in the user's  home  directory.  Note
       that  the  arguments  are  listed  in  ascending order of priority, with the contents of app_string being
       potentially overridden by commands in app_file, and commands in app_file potentially being overridden  by
       commands in user_file.

       You can call this function as many times as needed, the results being cumulative, but note that copies of
       any filenames specified via the app_file and user_file arguments are recorded internally  for  subsequent
       use  by the read-init-files key-binding function, so if you plan to call this function multiple times, be
       sure that the last call specifies the filenames that you want re-read when the  user  requests  that  the
       configuration files be re-read.

       Individual key sequences can also be bound and unbound using the gl_bind_keyseq() function.

         int gl_bind_keyseq(GetLine *gl, GlKeyOrigin origin,
                            const char *keyseq,
                            const char *action);

       The  origin argument specifies the priority of the binding, according to who it is being established for,
       and must be one of the following two values.

         GL_USER_KEY   -   The user requested this key-binding.
         GL_APP_KEY    -   This is a default binding set by the
                           application.

       When both user and application bindings for a given key-sequence have been specified,  the  user  binding
       takes  precedence.  The  application's  binding is subsequently reinstated if the user's binding is later
       unbound via either another to this function, or a call to gl_configure_getline().

       The keyseq argument specifies the key-sequence to be bound or unbound, and is expressed in the  same  way
       as in a ~/.teclarc configuration file. The action argument must either be a string containing the name of
       the action to bind the key-sequence to, or it must be NULL or "" to unbind the key-sequence.

CUSTOMIZED WORD COMPLETION

       If in your application, you would like to have TAB completion complete other things  in  addition  to  or
       instead  of filenames, you can arrange this by registering an alternate completion callback function, via
       a call to the gl_customize_completion() function.

         int gl_customize_completion(GetLine *gl, void *data,
                                     CplMatchFn *match_fn);

       The data argument provides a way for your application to pass arbitrary, application-specific information
       to  the  callback  function.  This  is  passed to the callback every time that it is called. It might for
       example, point to the symbol table from which  possible  completions  are  to  be  sought.  The  match_fn
       argument  specifies  the  callback  function  to  be  called.  The CplMatchFn function type is defined in
       libtecla.h, as is a CPL_MATCH_FN() macro that you can use to declare and  prototype  callback  functions.
       The   declaration   and   responsibilities   of   callback  functions  are  described  in  depth  in  the
       cpl_complete_word(3) man page.

       In brief, the callback function is responsible for looking backwards in the input  line,  back  from  the
       point  at  which the user pressed TAB, to find the start of the word being completed. It then must lookup
       possible completions of this word, and record them one by one in the WordCompletion object that is passed
       to  it  as  an argument, by calling the cpl_add_completion() function. If the callback function wishes to
       provide filename completion in addition to its own specific completions, it  has  the  option  of  itself
       calling  the  builtin file-name completion callback. This also, is documented in the cpl_complete_word(3)
       man page.

       Note that if you would like gl_get_line() to return the current input line when a  successful  completion
       is  been  made,  you can arrange this when you call cpl_add_completion(), by making the last character of
       the continuation suffix a newline character. If you do this, the input line will be  updated  to  display
       the completion, together with any contiuation suffix up to the newline character, then gl_get_line() will
       return this input line.

       If, for some reason, your callback function needs to write  something  to  the  terminal,  it  must  call
       gl_normal_io()  before  doing so. This will start a new line after the input line that is currently being
       edited, reinstate normal terminal I/O, and tell gl_get_line() that the input line will need to be redrawn
       when the callback returns.

ADDING COMPLETION ACTIONS

       In  the  previous  section  the  ability to customize the behavior of the only default completion action,
       complete-word, was described.  In this section the ability to install  additional  action  functions,  so
       that  different  types  of word completion can be bound to different key-sequences, is described. This is
       achieved by using the gl_completion_action() function.

         int gl_completion_action(GetLine *gl,
                                  void *data, CplMatchFn *match_fn,
                                  int list_only, const char *name,
                                  const char *keyseq);

       The data and match_fn arguments are as described in the  cpl_complete_word  man  page,  and  specify  the
       callback  function  that  should  be  invoked  to  identify possible completions.  The list_only argument
       determines whether the action that is being defined should  attempt  to  complete  the  word  as  far  as
       possible  in  the  input  line before displaying any possible ambiguous completions, or whether it should
       simply display the list of possible completions without touching the input line.  The  former  option  is
       selected  by  specifying  a  value  of  0,  and  the latter by specifying a value of 1. The name argument
       specifies the name by which configuration files and future invocations of this function should  refer  to
       the  action.  This  must  either  be the name of an existing completion action to be changed, or be a new
       unused name for a new action. Finally, the keyseq argument specifies the default key-sequence to bind the
       action to. If this is NULL, no new keysequence will be bound to the action.

       Beware that in order for the user to be able to change the key-sequence that is bound to actions that are
       installed in this manner, when you call gl_completion_action() to install a given action  for  the  first
       time,  you  should do this between calling new_GetLine() and the first call to gl_get_line().  Otherwise,
       when the user's configuration file is read on the first call to  gl_get_line(),  the  name  of  the  your
       additional  action  won't  be  known,  and any reference to it in the configuration file will generate an
       error.

       As discussed for gl_customize_completion(), if your callback function, for some reason,  needs  to  write
       anything to the terminal, it must call gl_normal_io() before doing so.

DEFINING CUSTOM ACTIONS

       Although the built-in key-binding actions are sufficient for the needs of most applications, occasionally
       a specialized application may need to define one or more custom actions,  bound  to  application-specific
       key-sequences.  For  example, a sales application would benefit from having a key-sequence that displayed
       the part name that corresponded to a part number preceding the cursor. Such a feature is  clearly  beyond
       the  scope of the built-in action functions. So for such special cases, the gl_register_action() function
       is provided.

         int gl_register_action(GetLine *gl, void *data,
                       GlActionFn *fn, const char *name,
                       const char *keyseq);

       This function lets the application register an external function, fn,  that  will  thereafter  be  called
       whenever  either the specified key-sequence, keyseq, is entered by the user, or the user enters any other
       key-sequence that the user subsequently binds to the specified action name, name, in their  configuration
       file.  The  data  argument can be a pointer to anything that the application wishes to have passed to the
       action function, fn, whenever that function is invoked.

       The action function, fn, should be declared using the following macro, which is defined in libtecla.h.

         #define GL_ACTION_FN(fn) GlAfterAction (fn)(GetLine *gl, \
                     void *data, int count, size_t curpos, \
                     const char *line)

       The gl and data arguments are those that were previously passed to gl_register_action() when  the  action
       function  was  registered.  The  count  argument  is  a numeric argument which the user has the option of
       entering using the digit-argument action, before invoking the action. If the user doesn't enter a number,
       then  the  count  argument is set to 1. Nominally this argument is interpreted as a repeat count, meaning
       that the action should be repeated that many times. In practice however, for some actions a repeat  count
       makes  little sense. In such cases, actions can either simply ignore the count argument, or use its value
       for a different purpose.

       A copy of the current input line is passed in the read-only line argument. The  current  cursor  position
       within  this string is given by the index contained in the curpos argument. Note that direct manipulation
       of the input line and the cursor position is not permitted. This is because the rules dicated by  various
       modes,  such as vi mode versus emacs mode, no-echo mode, and insert mode versus overstrike mode etc, make
       it too complex for an application writer to write a conforming  editing  action,  as  well  as  constrain
       future  changes  to the internals of gl_get_line(). A potential solution to this dilema would be to allow
       the action function to edit the line  using  the  existing  editing  actions.  This  is  currently  under
       consideration.

       If  the  action  function  wishes  to  write text to the terminal, without this getting mixed up with the
       displayed text of the input line, or read from the terminal without having to handle  raw  terminal  I/O,
       then  before  doing  either  of these operations, it must temporarily suspend line editing by calling the
       gl_normal_io() function. This function flushes any pending output to the terminal, moves  the  cursor  to
       the  start  of the line that follows the last terminal line of the input line, then restores the terminal
       to a state that is suitable for use with the C stdio facilities.  The  latter  includes  such  things  as
       restoring  the normal mapping of \n to \r\n, and, when in server mode, restoring the normal blocking form
       of terminal I/O. Having called this function, the action function can read from and write to the terminal
       without  the fear of creating a mess.  It isn't necessary for the action function to restore the original
       editing environment before it returns. This is done  automatically  by  gl_get_line()  after  the  action
       function  returns.   The  following  is  a simple example of an action function which writes the sentence
       "Hello world" on a new terminal line after the line being edited. When this function returns,  the  input
       line is redrawn on the line that follows the "Hello world" line, and line editing resumes.

         static GL_ACTION_FN(say_hello_fn)
         {
           if(gl_normal_io(gl))   /* Temporarily suspend editing */
             return GLA_ABORT;
           printf("Hello world\n");
           return GLA_CONTINUE;
         }

       Action functions must return one of the following values, to tell gl_get_line() how to procede.

         GLA_ABORT     -   Cause gl_get_line() to return NULL.
         GLA_RETURN    -   Cause gl_get_line() to return the
                           completed input line.
         GLA_CONTINUE  -   Resume command-line editing.

       Note  that  the name argument of gl_register_action() specifies the name by which a user can refer to the
       action in their configuration file. This allows them to re-bind the action to an alternate  key-seqeunce.
       In order for this to work, it is necessary to call gl_register_action() between calling new_GetLine() and
       the first call to gl_get_line().

HISTORY FILES

       To save the contents of the history buffer before quitting your  application,  and  subsequently  restore
       them when you next start the application, the following functions are provided.

        int gl_save_history(GetLine *gl, const char *filename,
                            const char *comment, int max_lines);
        int gl_load_history(GetLine *gl, const char *filename,
                            const char *comment);

       The filename argument specifies the name to give the history file when saving, or the name of an existing
       history file, when loading. This may contain home-directory and environment variable expressions, such as
       "~/.myapp_history" or "$HOME/.myapp_history".

       Along  with  each  history line, extra information about it, such as when it was entered by the user, and
       what its nesting level is, is recorded as a comment preceding the line in the history file. Writing  this
       as a comment allows the history file to double as a command file, just in case you wish to replay a whole
       session using it. Since comment prefixes differ in different languages, the comment argument is  provided
       for specifying the comment prefix. For example, if your application were a unix shell, such as the bourne
       shell, you would specify "#" here. Whatever you choose for the comment character, you  must  specify  the
       same  prefix  to  gl_load_history()  that you used when you called gl_save_history() to write the history
       file.

       The max_lines must be either -1 to specify that all lines in the history list be  saved,  or  a  positive
       number specifying a ceiling on how many of the most recent lines should be saved.

       Both  functions  return  non-zero  on  error,  after  writing  an  error  message  to  stderr.  Note that
       gl_load_history() does not consider the non-existence of a file to be an error.

MULTIPLE HISTORY LISTS

       If your application uses a single GetLine object for entering many different types of  input  lines,  you
       may  wish  gl_get_line() to distinguish the different types of lines in the history list, and only recall
       lines that match the current type of line. To support this requirement, gl_get_line() marks  lines  being
       recorded  in  the  history  list  with  an  integer identifier chosen by the application.  Initially this
       identifier  is  set  to  0  by  new_GetLine(),  but  it  can   be   changed   subsequently   by   calling
       gl_group_history().

         int gl_group_history(GetLine *gl, unsigned id);

       The  integer  identifier  id can be any number chosen by the application, but note that gl_save_history()
       and gl_load_history() preserve the association between identifiers and  historical  input  lines  between
       program invocations, so you should choose fixed identifiers for the different types of input line used by
       your application.

       Whenever gl_get_line() appends a new input line to the history list, the current  history  identifier  is
       recorded  with it, and when it is asked to recall a historical input line, it only recalls lines that are
       marked with the current identifier.

DISPLAYING HISTORY

       The history list can be displayed by calling gl_show_history().

         int gl_show_history(GetLine *gl, FILE *fp,
                             const char *fmt,
                             int all_groups,
                             int max_lines);

       This displays the current contents of the history list to the stdio output stream fp.  If  the  max_lines
       argument is greater than or equal to zero, then no more than this number of the most recent lines will be
       displayed. If the all_groups argument is non-zero, lines from all history groups are displayed. Otherwise
       just  those  of  the  currently  selected  history  group are displayed. The format string argument, fmt,
       determines how the line is displayed. This can contain arbitrary characters which are  written  verbatim,
       interleaved with any of the following format directives:

         %D  -  The date on which the line was originally
                entered, formatted like 2001-11-20.
         %T  -  The time of day when the line was entered,
                formatted like 23:59:59.
         %N  -  The sequential entry number of the line in
                the history buffer.
         %G  -  The number of the history group which the
                line belongs to.
         %%  -  A literal % character.
         %H  -  The history line itself.

       Thus a format string like "%D %T  %H0 would output something like:

         2001-11-20 10:23:34  Hello world

       Note the inclusion of an explicit newline character in the format string.

LOOKING UP HISTORY

       The gl_lookup_history() function allows the calling application to look up lines in the history list.

         typedef struct {
           const char *line;    /* The requested historical */
                                /*  line. */
           unsigned group;      /* The history group to which */
                                /*  the line belongs. */
           time_t timestamp;    /* The date and time at which */
                                /*  the line was originally */
                                /*  entered. */
         } GlHistoryLine;

         int gl_lookup_history(GetLine *gl, unsigned long id,
                               GlHistoryLine *hline);

       The  id  argument  indicates  which line to look up, where the first line that was entered in the history
       list after new_GetLine() was called, is denoted by 0, and subsequently entered  lines  are  denoted  with
       successively  higher numbers. Note that the range of lines currently preserved in the history list can be
       queried by calling the gl_range_of_history() function, described later. If the requested line is  in  the
       history  list, the details of the line are recorded in the variable pointed to by the hline argument, and
       1 is returned. Otherwise 0 is returned, and the variable pointed to by hline is left unchanged.

       Beware that the string returned in hline->line is part of the history buffer, so it must not be  modified
       by  the  caller,  and  will  be  recycled on the next call to any function that takes gl as its argument.
       Therefore you should make a private copy of this string if you need to keep it around.

MANUAL HISTORY ARCHIVAL

       By default, whenever a line is entered by the user, it is automatically appended  to  the  history  list,
       just  before  gl_get_line()  returns  the  line  to  the  caller.  This is convenient for the majority of
       applications, but there are also applications that need finer grained control over what gets added to the
       history  list.  In  such cases, the automatic addition of entered lines to the history list can be turned
       off by calling the gl_automatic_history() function.

         int gl_automatic_history(GetLine *gl, int enable);

       If this function is called with its enable argument set to 0, gl_get_line() won't  automatically  archive
       subsequently  entered  lines.  Automatic  archiving  can  be  re-enabled at a later time, by calling this
       function again, with its enable argument set to 1.  While automatic history archiving  is  disabled,  the
       calling application can use the gl_append_history() to append lines to the history list as needed.

         int gl_append_history(GetLine *gl, const char *line);

       The  line  argument  specifies  the  line  to  be  added  to  the history list. This must be a normal ' '
       terminated string. If this string contains any newline characters, the line that  gets  archived  in  the
       history  list  will  be  terminated  by  the  first  of these. Otherwise it will be terminated by the ' '
       terminator.  If the line is  longer  than  the  maximum  input  line  length,  that  was  specified  when
       new_GetLine()  was  called,  when the line is recalled, it will get truncated to the actual gl_get_line()
       line length.

       If successful, gl_append_history() returns 0. Otherwise it returns non-zero, and sets errno to one of the
       following values.

          EINVAL  -  One of the arguments passed to
                     gl_append_history() was NULL.
          ENOMEM  -  The specified line was longer than the allocated
                     size of the history buffer (as specified when
                     new_GetLine() was called), so it couldn't be
                     archived.

       A  textual  description  of the error can optionally be obtained by calling gl_error_message(). Note that
       after such an error, the history list remains in a valid state to receive new history lines, so there  is
       little harm in simply ignoring the return status of gl_append_history().

MISCELLANEOUS HISTORY CONFIGURATION

       If  you  wish  to  change  the  size  of  the history buffer that was originally specified in the call to
       new_GetLine(), you can do so with the gl_resize_history() function.

         int gl_resize_history(GetLine *gl, size_t histlen);

       The histlen argument specifies the new size in bytes, and if you specify this as 0, the  buffer  will  be
       deleted.

       As  mentioned  in  the discussion of new_GetLine(), the number of lines that can be stored in the history
       buffer, depends on the lengths of the individual lines. For example, a 1000  byte  buffer  could  equally
       store 10 lines of average length 100 bytes, or 2 lines of average length 50 bytes. Although the buffer is
       never expanded when new lines are added, a list of pointers into the buffer does get expanded when needed
       to  accommodate the number of lines currently stored in the buffer. To place an upper limit on the number
       of lines in the buffer, and thus a ceiling on the amount of memory used in this list, you  can  call  the
       gl_limit_history() function.

         void gl_limit_history(GetLine *gl, int max_lines);

       The  max_lines  should either be a positive number >= 0, specifying an upper limit on the number of lines
       in the buffer, or be -1 to cancel any previously specified limit. When a limit is  in  effect,  only  the
       max_lines most recently appended lines are kept in the buffer. Older lines are discarded.

       To discard lines from the history buffer, use the gl_clear_history() function.

         void gl_clear_history(GetLine *gl, int all_groups);

       The  all_groups  argument tells the function whether to delete just the lines associated with the current
       history group (see gl_group_history()), or all historical lines in the buffer.

       The gl_toggle_history() function allows you to toggle history on  and  off  without  losing  the  current
       contents of the history list.

         void gl_toggle_history(GetLine *gl, int enable);

       Setting  the  enable argument to 0 turns off the history mechanism, and setting it to 1 turns it back on.
       When history is turned off, no new lines will be added to the  history  list,  and  history  lookup  key-
       bindings will act as though there is nothing in the history buffer.

QUERYING HISTORY INFORMATION

       The configured state of the history list can be queried with the gl_history_state() function.

         typedef struct {
           int enabled;     /* True if history is enabled */
           unsigned group;  /* The current history group */
           int max_lines;   /* The current upper limit on the */
                            /*  number of lines in the history */
                            /*  list, or -1 if unlimited. */
         } GlHistoryState;

         void gl_state_of_history(GetLine *gl,
                                  GlHistoryState *state);

       On return, the status information is recorded in the variable pointed to by the state argument.

       The gl_range_of_history() function returns the number and range of lines in the history list.

       typedef struct {
         unsigned long oldest;  /* The sequential entry number */
                                /*  of the oldest line in the */
                                /*  history list. */
         unsigned long newest;  /* The sequential entry number */
                                /*  of the newest line in the */
                                /*  history list. */
         int nlines;            /* The number of lines in the */
                                /*  history list. */
       } GlHistoryRange;

       void gl_range_of_history(GetLine *gl, GlHistoryRange *range);

       The  return values are recorded in the variable pointed to by the range argument. If the nlines member of
       this structure is greater than zero, then the oldest and newest members report the range of lines in  the
       list, and newest=oldest+nlines-1.  Otherwise they are both zero.

       The  gl_size_of_history()  function  returns  the  total size of the history buffer and the amount of the
       buffer that is currently occupied.

         typedef struct {
           size_t size;      /* The size of the history buffer */
                             /*  (bytes). */
           size_t used;      /* The number of bytes of the */
                             /*  history buffer that are */
                             /*  currently occupied. */
         } GlHistorySize;

         void gl_size_of_history(GetLine *gl, GlHistorySize *size);

       On return, the size information is recorded in the variable pointed to by the size argument.

CHANGING TERMINALS

       The new_GetLine() constructor function assumes that input is to be read from stdin, and output written to
       stdout. The following function allows you to switch to different input and output streams.

         int gl_change_terminal(GetLine *gl, FILE *input_fp,
                                FILE *output_fp, const char *term);

       The  gl  argument  is the object that was returned by new_GetLine().  The input_fp argument specifies the
       stream to read from, and output_fp specifies the stream to be written to. Only if both of these refer  to
       a terminal, will interactive terminal input be enabled.  Otherwise gl_get_line() will simply call fgets()
       to read command input. If both streams refer to a terminal, then they must refer to  the  same  terminal,
       and  the type of this terminal must be specified via the term argument. The value of the term argument is
       looked up in the terminal information database (terminfo or termcap), in order to determine which special
       control  sequences  are  needed  to  control  various aspects of the terminal. new_GetLine() for example,
       passes the return value of getenv("TERM") in this argument. Note that if one  or  both  of  input_fp  and
       output_fp don't refer to a terminal, then it is legal to pass NULL instead of a terminal type.

       Note that if you want to pass file descriptors to gl_change_terminal(), you can do this by creating stdio
       stream wrappers using the POSIX fdopen() function.

EXTERNAL EVENT HANDLING

       By default, gl_get_line() doesn't return until either a complete input line has been entered by the user,
       or  an  error  occurs. In programs that need to watch for I/O from other sources than the terminal, there
       are two options.

         1. Use the functions described in the
            gl_io_mode(3) man page to switch
            gl_get_line() into non-blocking server mode. In this mode,
            gl_get_line() becomes a non-blocking, incremental
            line-editing function that can safely be called from
            an external event loop. Although this is a very
            versatile method, it involves taking on some
            responsibilities that are normally performed behind
            the scenes by gl_get_line().

         2. While gl_get_line() is waiting for keyboard
            input from the user, you can ask it to also watch for
            activity on arbitrary file descriptors, such as
            network sockets, pipes etc, and have it call functions
            of your choosing when activity is seen. This works on
            any system that has the select() system call,
            which is most, if not all flavors of unix.

       Registering a file descriptor to be watched by gl_get_line() involves calling the gl_watch_fd() function.

         int gl_watch_fd(GetLine *gl, int fd, GlFdEvent event,
                         GlFdEventFn *callback, void *data);

       If this returns non-zero, then it means that either your arguments are invalid,  or  that  this  facility
       isn't supported on the host system.

       The  fd argument is the file descriptor to be watched. The event argument specifies what type of activity
       is of interest, chosen from the following enumerated values:

         GLFD_READ   -  Watch for the arrival of data to be read.
         GLFD_WRITE  -  Watch for the ability to write to the file
                        descriptor without blocking.
         GLFD_URGENT -  Watch for the arrival of urgent
                        out-of-band data on the file descriptor.

       The callback argument is the function to call when the selected activity is seen. It  should  be  defined
       with the following macro, which is defined in libtecla.h.

         #define GL_FD_EVENT_FN(fn) GlFdStatus (fn)(GetLine *gl, \
                                             void *data, int fd, \
                                             GlFdEvent event)

       The  data  argument of the gl_watch_fd() function is passed to the callback function for its own use, and
       can point to anything you like, including NULL. The file descriptor  and  the  event  argument  are  also
       passed  to the callback function, and this potentially allows the same callback function to be registered
       to more than one type of event and/or more than one file descriptor. The return  value  of  the  callback
       function should be one of the following values.

         GLFD_ABORT    -  Tell gl_get_line() to abort. When this
                          happens, gl_get_line() returns
                          NULL, and a following call to
                          gl_return_status() will return
                          GLR_FDABORT. Note that if the
                          application needs errno always to
                          have a meaningful value when
                          gl_get_line() returns NULL,
                          the callback function should set
                          errno appropriately.
         GLFD_REFRESH  -  Redraw the input line then continue
                          waiting for input. Return this if
                          your callback wrote to the terminal.
         GLFD_CONTINUE -  Continue to wait for input, without
                          redrawing the line.

       Note  that  before  calling  the  callback,  gl_get_line() blocks most signals, and leaves its own signal
       handlers installed, so if you need to catch a particular signal you will need to both temporarily install
       your  own  signal  handler,  and unblock the signal. Be sure to re-block the signal (if it was originally
       blocked) and reinstate the original signal handler, if any, before returning.

       If the callback function needs  to  read  or  write  to  the  terminal,  it  should  ideally  first  call
       gl_normal_io(gl)  to  temporarily  suspend  line  editing.  This  will restore the terminal to canonical,
       blocking-I/O, mode, and move the cursor to the start of a new terminal line.  Later,  when  the  callback
       returns,  gl_get_line()  will  notice that gl_normal_io() was called, redisplay the input line and resume
       editing. Note that in this case the return values, GLFD_REFRESH and GLFD_CONTINUE are equivalent.

       To support cases where the  callback  function  calls  a  third-party  function0 isire-enabledobefore the
       unpredictably  writes  to  the  terminal,  the  automatic conversion of "0 to "
       callback function is called. If the callack knows that the third-party function wrote to the terminal, it
       should then return the GLFD_REFRESH return value, to tell gl_get_line() to redisplay the input line.

       To  remove  a  callback  function  that  you previously registered for a given file descriptor and event,
       simply call gl_watch_fd() with the same file descriptor and event arguments, but with a callback argument
       of 0. The data argument is ignored in this case.

SETTING AN INACTIVITY TIMEOUT

       On  systems  with  the  select()  system call, the gl_inactivity_timeout() function can be used to set or
       cancel an inactivity timeout. Inactivity in this case refers both to keyboard input, and to  I/O  on  any
       file descriptors registered by prior and subsequent calls to gl_watch_fd(). On oddball systems that don't
       have select(), this call has no effect.

         int gl_inactivity_timeout(GetLine *gl, GlTimeoutFn *callback,
                            void *data, unsigned long sec,
                            unsigned long nsec);

       The timeout is specified in the form of  an  integral  number  of  seconds  and  an  integral  number  of
       nanoseconds,  via the sec and nsec arguments respectively. Subsequently, whenever no activity is seen for
       this time period, the function specified via the callback  argument  is  called.  The  data  argument  of
       gl_inactivity_timeout() is passed verbatim to this callback function whenever it is invoked, and can thus
       be used to pass arbitrary application-specific information  to  the  callback.  The  following  macro  is
       provided in libtecla.h for applications to use to declare and prototype timeout callback functions.

         #define GL_TIMEOUT_FN(fn) \
                      GlAfterTimeout (fn)(GetLine *gl, void *data)

       On  returning,  the application's callback is expected to return one of the following enumerators to tell
       gl_get_line() how to procede after the timeout has been handled by the callback.

         GLTO_ABORT    -  Tell gl_get_line() to abort. When
                          this happens, gl_get_line() will
                          return NULL, and a following call
                          to gl_return_status() will return
                          GLR_TIMEOUT. Note that if the
                          application needs errno always to
                          have a meaningful value when
                          gl_get_line() returns NULL,
                          the callback function should set
                          errno appropriately.
         GLTO_REFRESH  -  Redraw the input line, then continue
                          waiting for input. You should return
                          this value if your callback wrote to the
                          terminal without having first called
                          gl_normal_io(gl).
         GLTO_CONTINUE -  In normal blocking-I/O mode, continue to
                          wait for input, without redrawing the
                          user's input line.
                          In non-blocking server I/O mode (see
                          gl_io_mode(3)), cause gl_get_line()
                          to act as though I/O blocked. This means
                          that gl_get_line() will immediately
                          return NULL, and a following call
                          to gl_return_status() will return
                          GLR_BLOCKED.

       Note that before calling the callback, gl_get_line() blocks most  signals,  and  leaves  its  own  signal
       handlers installed, so if you need to catch a particular signal you will need to both temporarily install
       your own signal handler, and unblock the signal. Be sure to re-block the signal  (if  it  was  originally
       blocked) and reinstate the original signal handler, if any, before returning.

       If  the  callback  function  needs  to  read  or  write  to  the  terminal,  it should ideally first call
       gl_normal_io(gl) to temporarily suspend line editing.  This  will  restore  the  terminal  to  canonical,
       blocking-I/O,  mode,  and  move  the cursor to the start of a new terminal line. Later, when the callback
       returns, gl_get_line() will notice that gl_normal_io() was called, redisplay the input  line  and  resume
       editing. Note that in this case the return values, GLTO_REFRESH and GLTO_CONTINUE are equivalent.

       To  support  cases  where  the  callback  function  calls  a  third-party f0ncisonre-enabledasbeforey the
       unpredictably writes to the terminal, the automatic conversion of "0  to  "
       callback function is called. If the callack knows that the third-party function wrote to the terminal, it
       should then return the GLTO_REFRESH return value, to tell gl_get_line() to redisplay the input line.

       Note that although the timeout argument includes a nano-second component, few computer  clocks  presently
       have  resolutions  that  are finer than a few milliseconds, so asking for less than a few milliseconds is
       equivalent to requesting zero seconds on a lot of systems. If this would be a problem,  you  should  base
       your timeout selection on the actual resolution of the host clock (eg. by calling sysconf(_SC_CLK_TCK)).

       To  turn  off  timeouts,  simply  call  gl_inactivity_timeout()  with  a callback argument of 0. The data
       argument is ignored in this case.

SIGNAL HANDLING DEFAULTS

       By default, the gl_get_line() function intercepts a number of signals. This is particularly important for
       signals which would by default terminate the process, since the terminal needs to be restored to a usable
       state before this  happens.  In  this  section,  the  signals  that  are  trapped  by  default,  and  how
       gl_get_line()  responds  to  them,  is  described.  Changing these defaults is the topic of the following
       section.

       When the following subset of signals are caught, gl_get_line() first restores the terminal  settings  and
       signal  handling  to  how  they  were  before  gl_get_line() was called, resends the signal, to allow the
       calling application's signal handlers to handle it, then  if  the  process  still  exists,  gl_get_line()
       returns NULL and sets errno as specified below.

        SIGINT  -  This signal is generated both by the keyboard
                   interrupt key (usually ^C), and the keyboard
                   break key.

                   errno=EINTR

        SIGHUP  -  This signal is generated when the controlling
                   terminal exits.

                   errno=ENOTTY

        SIGPIPE -  This signal is generated when a program attempts
                   to write to a pipe who's remote end isn't being
                   read by any process. This can happen for example
                   if you have called gl_change_terminal() to
                   redirect output to a pipe hidden under a pseudo
                   terminal.

                   errno=EPIPE

        SIGQUIT -  This signal is generated by the keyboard quit
                   key (usually ^\).

                   errno=EINTR

        SIGABRT -  This signal is generated by the standard C,
                   abort() function. By default it both
                   terminates the process and generates a core
                   dump.

                   errno=EINTR

        SIGTERM -  This is the default signal that the UN*X
                   kill command sends to processes.

                   errno=EINTR

       Note  that  in  the  case  of  all  of  the  above signals, POSIX mandates that by default the process is
       terminated, with the addition of a core dump in the case of the SIGQUIT signal. In other  words,  if  the
       calling  application doesn't override the default handler by supplying its own signal handler, receipt of
       the corresponding signal will terminate the application before gl_get_line() returns.

       If gl_get_line() aborts with errno set to EINTR, you can find out what signal  caused  it  to  abort,  by
       calling the following function.

         int gl_last_signal(const GetLine *gl);

       This  returns  the  numeric code (eg. SIGINT) of the last signal that was received during the most recent
       call to gl_get_line(), or -1 if no signals were received.

       On systems that support it, when a SIGWINCH (window change) signal is received, gl_get_line() queries the
       terminal  to  find  out  its  new  size, redraws the current input line to accommodate the new size, then
       returns to waiting for keyboard input from the user. Unlike other signals, this signal  isn't  resent  to
       the application.

       Finally,  the  following signals cause gl_get_line() to first restore the terminal and signal environment
       to that which prevailed before gl_get_line() was called, then resend the signal to  the  application.  If
       the  process still exists after the signal has been delivered, then gl_get_line() then re-establishes its
       own signal handlers, switches the terminal back to raw mode, redisplays the input line, and goes back  to
       awaiting terminal input from the user.

        SIGCONT    -  This signal is generated when a suspended
                      process is resumed.

        SIGPOLL    -  On SVR4 systems, this signal notifies the
                      process of an asynchronous I/O event. Note
                      that under 4.3+BSD, SIGIO and SIGPOLL are
                      the same. On other systems, SIGIO is ignored
                      by default, so gl_get_line() doesn't
                      trap it by default.

        SIGPWR     -  This signal is generated when a power failure
                      occurs (presumably when the system is on a
                      UPS).

        SIGALRM    -  This signal is generated when a timer
                      expires.

        SIGUSR1    -  An application specific signal.

        SIGUSR2    -  Another application specific signal.

        SIGVTALRM  -  This signal is generated when a virtual
                      timer expires (see man setitimer(2)).

        SIGXCPU    -  This signal is generated when a process
                      exceeds its soft CPU time limit.

        SIGXFSZ    -  This signal is generated when a process
                      exceeds its soft file-size limit.

        SIGTSTP    -  This signal is generated by the terminal
                      suspend key, which is usually ^Z, or the
                      delayed terminal suspend key, which is
                      usually ^Y.

        SIGTTIN    -  This signal is generated if the program
                      attempts to read from the terminal while the
                      program is running in the background.

        SIGTTOU    -  This signal is generated if the program
                      attempts to write to the terminal while the
                      program is running in the background.

       Obviously  not  all  of  the  above  signals  are  supported  on  all systems, so code to support them is
       conditionally compiled into the tecla library.

       Note that if SIGKILL or SIGPOLL, which by definition can't be caught, or any of  the  hardware  generated
       exception signals, such as SIGSEGV, SIGBUS and SIGFPE, are received and unhandled while gl_get_line() has
       the terminal in raw mode, the program will be terminated without the terminal having been restored  to  a
       usable  state.  In  practice,  job-control  shells  usually  reset  the  terminal settings when a process
       relinquishes the controlling terminal, so this is only a problem with older shells.

CUSTOMIZED SIGNAL HANDLING

       The previous section listed the signals that  gl_get_line()  traps  by  default,  and  described  how  it
       responds  to  them.  This  section  describes how to both add and remove signals from the list of trapped
       signals, and how to specify how gl_get_line() should respond to a given signal.

       If you don't need gl_get_line() to do anything in response to a signal that it normally  traps,  you  can
       tell to gl_get_line() to ignore that signal by calling gl_ignore_signal().

         int gl_ignore_signal(GetLine *gl, int signo);

       The  signo  argument  is  the  number  of  the  signal (eg. SIGINT) that you want to have ignored. If the
       specified signal isn't currently one of those being trapped, this function does nothing.

       The gl_trap_signal() function allows you to either add a new signal to the list that gl_get_line() traps,
       or modify how it responds to a signal that it already traps.

         int gl_trap_signal(GetLine *gl, int signo, unsigned flags,
                            GlAfterSignal after, int errno_value);

       The signo argument is the number of the signal that you wish to have trapped. The flags argument is a set
       of flags which determine the environment in which the application's signal handler is invoked, the  after
       argument  tells  gl_get_line() what to do after the application's signal handler returns, and errno_value
       tells gl_get_line() what to set errno to if told to abort.

       The flags argument is a bitwise OR of zero or more of the following enumerators:

         GLS_RESTORE_SIG  -  Restore the caller's signal
                             environment while handling the
                             signal.

         GLS_RESTORE_TTY  -  Restore the caller's terminal settings
                             while handling the signal.

         GLS_RESTORE_LINE -  Move the cursor to the start of the
                             line following the input line before
                             invoking the application's signal
                             handler.

         GLS_REDRAW_LINE  -  Redraw the input line when the
                             application's signal handler returns.

         GLS_UNBLOCK_SIG  -  Normally, if the calling program has
                             a signal blocked (man sigprocmask),
                             gl_get_line() does not trap that
                             signal. This flag tells gl_get_line()
                             to trap the signal and unblock it for
                             the duration of the call to
                             gl_get_line().

         GLS_DONT_FORWARD -  If this flag is included, the signal
                             will not be forwarded to the signal
                             handler of the calling program.

       Two commonly useful flag combinations are also enumerated as follows:

         GLS_RESTORE_ENV   = GLS_RESTORE_SIG | GLS_RESTORE_TTY |
                             GLS_REDRAW_LINE

         GLS_SUSPEND_INPUT = GLS_RESTORE_ENV | GLS_RESTORE_LINE

       If your signal handler, or the default system signal handler for this signal, if you  haven't  overridden
       it,  never  either  writes  to the terminal, nor suspends or terminates the calling program, then you can
       safely set the flags argument to 0.

       If your signal handler always writes to the terminal, reads  from  it,  or  suspends  or  terminates  the
       program, you should specify the flags argument as GL_SUSPEND_INPUT, so that:

       1. The cursor doesn't get left in the middle of the input
          line.
       2. So that the user can type in input and have it echoed.
       3. So that you don't need to end each output line with
          \r\n, instead of just \n.

       The  GL_RESTORE_ENV  combination is the same as GL_SUSPEND_INPUT, except that it doesn't move the cursor,
       and if your signal handler doesn't read or write anything to the terminal, the user won't see any visible
       indication  that  a  signal  was  caught.  This  can  be  useful  if  you have a signal handler that only
       occasionally writes to the terminal, where using  GL_SUSPEND_LINE  would  cause  the  input  line  to  be
       unnecessarily  duplicated  when nothing had been written to the terminal.  Such a signal handler, when it
       does write to the terminal, should be sure to start a new line at  the  start  of  its  first  write,  by
       writing  a  \n  character,  and should be sure to leave the cursor on a new line before returning. If the
       signal arrives while the user is entering a line that only occupies a signal terminal  line,  or  if  the
       cursor  is  on  the  last  terminal  line  of  a  longer  input  line,  this will have the same effect as
       GL_SUSPEND_INPUT. Otherwise it will start writing on a line that already contains part of  the  displayed
       input  line.   This  doesn't  do  any  harm,  but  it looks a bit ugly, which is why the GL_SUSPEND_INPUT
       combination is better if you know that you are always going to be writing to the terminal.

       The after argument, which determines what gl_get_line()  does  after  the  application's  signal  handler
       returns (if it returns), can take any one of the following values:

         GLS_RETURN   - Return the completed input line, just as
                        though the user had pressed the return
                        key.

         GLS_ABORT    - Cause gl_get_line() to abort. When
                        this happens, gl_get_line() returns
                        NULL, and a following call to
                        gl_return_status() will return
                        GLR_SIGNAL. Note that if the
                        application needs errno always to
                        have a meaningful value when
                        gl_get_line() returns NULL,
                        the callback function should set
                        errno appropriately.
         GLS_CONTINUE - Resume command line editing.

       The errno_value argument is intended to be combined with the GLS_ABORT option, telling gl_get_line() what
       to set the standard errno variable to before returning NULL to the calling program. It can also, however,
       be  used  with  the GL_RETURN option, in case you wish to have a way to distinguish between an input line
       that was entered using the return key, and one that was entered by the receipt of a signal.

RELIABLE SIGNAL HANDLING

       Signal handling is suprisingly hard to do reliably without race conditions. In  gl_get_line()  a  lot  of
       care  has been taken to allow applications to perform reliable signal handling around gl_get_line(). This
       section explains how to make use of this.

       As an example of the problems that can arise if the application isn't  written  correctly,  imagine  that
       one's  application  has a SIGINT signal handler that sets a global flag. Now suppose that the application
       tests this flag just before invoking gl_get_line(). If a SIGINT signal happens  to  be  received  in  the
       small  window  of  time  between  the statement that tests the value of this flag, and the statement that
       calls gl_get_line(), then gl_get_line() will not see the signal,  and  will  not  be  interrupted.  As  a
       result,  the  application  won't be able to respond to the signal until the user gets around to finishing
       entering the input line and gl_get_line() returns. Depending on the application, this might or might  not
       be a disaster, but at the very least it would puzzle the user.

       The way to avoid such problems is to do the following.

       1. If needed, use the gl_trap_signal() function to
          configure gl_get_line() to abort when important
          signals are caught.

       2. Configure gl_get_line() such that if any of the
          signals that it catches are blocked when
          gl_get_line() is called, they will be unblocked
          automatically during times when gl_get_line() is
          waiting for I/O. This can be done either
          on a per signal basis, by calling the
          gl_trap_signal() function, and specifying the
          GLS_UNBLOCK attribute of the signal, or globally by
          calling the gl_catch_blocked() function.

            void gl_catch_blocked(GetLine *gl);

          This function simply adds the GLS_UNBLOCK attribute
          to all of the signals that it is currently configured to
          trap.

       3. Just before calling gl_get_line(), block delivery
          of all of the signals that gl_get_line() is
          configured to trap. This can be done using the POSIX
          sigprocmask() function in conjunction with the
          gl_list_signals() function.

             int gl_list_signals(GetLine *gl, sigset_t *set);

          This function returns the set of signals that it is
          currently configured to catch in the set argument,
          which is in the form required by sigprocmask().

       4. In the example, one would now test the global flag that
          the signal handler sets, knowing that there is now no
          danger of this flag being set again until
          gl_get_line() unblocks its signals while performing
          I/O.

       5. Eventually gl_get_line() returns, either because
          a signal was caught, an error occurred, or the user
          finished entering their input line.

       6. Now one would check the global signal flag again, and if
          it is set, respond to it, and zero the flag.

       7. Use sigprocmask() to unblock the signals that were
          blocked in step 3.

       The  same  technique  can  be  used  around certain POSIX signal-aware functions, such as sigsetjmp() and
       sigsuspend(), and in particular, the former of these two  functions  can  be  used  in  conjunction  with
       siglongjmp() to implement race-condition free signal handling around other long-running system calls. The
       way to do this, is explained next, by showing how gl_get_line() manages to reliably trap  signals  around
       calls to functions like read() and select() without race conditions.

       The  first  thing  that  gl_get_line()  does,  whenever  it  is called, is to use the POSIX sigprocmask()
       function to block the delivery of all of the signals that it is currently configured to  catch.  This  is
       redundant  if  the  application  has  already blocked them, but it does no harm. It undoes this step just
       before returning.

       Whenever gl_get_line() needs to call read() or select() to wait for input from the user, it  first  calls
       the  POSIX  sigsetjmp()  function, being sure to specify a non-zero value for its savesigs argument.  The
       reason for the latter argument will become clear shortly.

       If sigsetjmp() returns zero, gl_get_line() then does the following.

       a. It uses the POSIX sigaction() function to register
          a temporary signal handler to all of the signals that it
          is configured to catch. This signal handler does two
          things.

          1. It records the number of the signal that was received
             in a file-scope variable.

          2. It then calls the POSIX siglongjmp()
             function using the buffer that was passed to
             sigsetjmp() for its first argument, and
             a non-zero value for its second argument.

          When this signal handler is registered, the sa_mask
          member of the struct sigaction act argument of the
          call to sigaction() is configured to contain all of
          the signals that gl_get_line() is catching. This
          ensures that only one signal will be caught at once by
          our signal handler, which in turn ensures that multiple
          instances of our signal handler don't tread on each
          other's toes.

       b. Now that the signal handler has been set up,
          gl_get_line() unblocks all of the signals that it
          is configured to catch.

       c. It then calls the read() or select() system
          calls to wait for keyboard input.

       d. If this system call returns (ie. no signal is received),
          gl_get_line() blocks delivery of the signals of
          interest again.

       e. It then reinstates the signal handlers that were
          displaced by the one that was just installed.

       Alternatively, if sigsetjmp() returns non-zero, this means that one of  the  signals  being  trapped  was
       caught while the above steps were executing. When this happens, gl_get_line() does the following.

       First,  note  that  when  a call to siglongjmp() causes sigsetjmp() to return, provided that the savesigs
       argument of sigsetjmp() was non-zero, as specified above, the signal process mask is restored to  how  it
       was  when  sigsetjmp()  was  called.  This  is the important difference between sigsetjmp() and the older
       problematic setjmp(), and is the essential ingredient that makes it possible  to  avoid  signal  handling
       race  conditions.   Because  of  this  we  are  guaranteed that all of the signals that we blocked before
       calling sigsetjmp() are blocked again as soon as any signal is caught. The  following  statements,  which
       are then executed, are thus guaranteed to be executed without any further signals being caught.

       1. If so instructed by the gl_get_line() configuration
          attributes of the signal that was caught,
          gl_get_line() restores the terminal attributes to
          the state that they had when gl_get_line() was
          called. This is particularly important for signals that
          suspend or terminate the process, since otherwise the
          terminal would be left in an unusable state.

       2. It then reinstates the application's signal handlers.

       3. Then it uses the C standard-library raise()
          function to re-send the application the signal that
          was caught.

       3. Next it unblocks delivery of the signal that we just
          sent. This results in the signal that was just sent
          via raise(), being caught by the application's
          original signal handler, which can now handle it as it
          sees fit.

       4. If the signal handler returns (ie. it doesn't terminate
          the process), gl_get_line() blocks delivery of the
          above signal again.

       5. It then undoes any actions performed in the first of the
          above steps, and redisplays the line, if the signal
          configuration calls for this.

       6. gl_get_line() then either resumes trying to
          read a character, or aborts, depending on the
          configuration of the signal that was caught.

       What  the  above  steps  do  in  essence  is  to  take  asynchronously  delivered signals and handle them
       synchronously, one at a time, at a point in the code where gl_get_line() has complete  control  over  its
       environment.

THE TERMINAL SIZE

       On  most  systems  the combination of the TIOCGWINSZ ioctl and the SIGWINCH signal is used to maintain an
       accurate idea of the terminal size. The terminal size is newly queried every time that  gl_get_line()  is
       called and whenever a SIGWINCH signal is received.

       On  the  few  systems  where this mechanism isn't available, at startup new_GetLine() first looks for the
       LINES and COLUMNS environment variables.  If these aren't found, or they contain unusable values, then if
       a  terminal  information database like terminfo or termcap is available, the default size of the terminal
       is looked up in this database. If this too fails to provide the terminal  size,  a  default  size  of  80
       columns by 24 lines is used.

       Even  on systems that do support ioctl(TIOCGWINSZ), if the terminal is on the other end of a serial line,
       the terminal driver generally has no way of detecting when a  resize  occurs  or  of  querying  what  the
       current  size  is.  In  such  cases  no  SIGWINCH  is sent to the process, and the dimensions returned by
       ioctl(TIOCGWINSZ) aren't correct. The only way to handle such instances is to provide a way for the  user
       to  enter  a  command that tells the remote system what the new size is. This command would then call the
       gl_set_term_size() function to tell gl_get_line() about the change in size.

         int gl_set_term_size(GetLine *gl, int ncolumn, int nline);

       The ncolumn and nline arguments are used to specify the new dimensions of the terminal, and must  not  be
       less than 1. On systems that do support ioctl(TIOCGWINSZ), this function first calls ioctl(TIOCSWINSZ) to
       tell the terminal driver about the change in  size.  In  non-blocking  server-I/O  mode,  if  a  line  is
       currently  being  input,  the input line is then redrawn to accommodate the changed size. Finally the new
       values are recorded in gl for future use by gl_get_line().

       The gl_terminal_size() function allows you to query the current size of  the  terminal,  and  install  an
       alternate fallback size for cases where the size isn't available.  Beware that the terminal size won't be
       available if reading from a pipe or a file, so the default values can be important even on  systems  that
       do support ways of finding out the terminal size.

         typedef struct {
           int nline;        /* The terminal has nline lines */
           int ncolumn;      /* The terminal has ncolumn columns */
         } GlTerminalSize;

         GlTerminalSize gl_terminal_size(GetLine *gl,
                                         int def_ncolumn,
                                         int def_nline);

       This  function  first  updates gl_get_line()'s fallback terminal dimensions, then records its findings in
       the return value.

       The def_ncolumn and def_nline specify the default number of terminal columns and  lines  to  use  if  the
       terminal size can't be determined via ioctl(TIOCGWINSZ) or environment variables.

HIDING WHAT YOU TYPE

       When  entering  sensitive  information,  such  as passwords, it is best not to have the text that you are
       entering echoed on the terminal.  Furthermore, such text should not be  recorded  in  the  history  list,
       since  somebody  finding your terminal unattended could then recall it, or somebody snooping through your
       directories could see it in your history file. With this in mind, the gl_echo_mode() function allows  you
       to  toggle  on  and  off  the  display  and archival of any text that is subsequently entered in calls to
       gl_get_line().

         int gl_echo_mode(GetLine *gl, int enable);

       The enable argument specifies whether  entered  text  should  be  visible  or  not.  If  it  is  0,  then
       subsequently  entered  lines will not be visible on the terminal, and will not be recorded in the history
       list. If it is 1, then subsequent input lines will be displayed as they are entered,  and  provided  that
       history  hasn't been turned off via a call to gl_toggle_history(), then they will also be archived in the
       history list. Finally, if the enable argument is -1, then the  echoing  mode  is  left  unchanged,  which
       allows  you to non-destructively query the current setting via the return value. In all cases, the return
       value of the function is 0 if echoing was disabled before the function  was  called,  and  1  if  it  was
       enabled.

       When  echoing is turned off, note that although tab completion will invisibly complete your prefix as far
       as possible, ambiguous completions will not be displayed.

SINGLE CHARACTER QUERIES

       Using gl_get_line() to query the user for a single character reply, is inconvenient for the  user,  since
       they  must  hit  the enter or return key before the character that they typed is returned to the program.
       Thus the gl_query_char() function has been provided for single character queries like this.

         int gl_query_char(GetLine *gl, const char *prompt,
                           char defchar);

       This function displays the specified prompt at the start of a new line, and waits for the user to type  a
       character.  When  the  user  types  a  character, gl_query_char() displays it to the right of the prompt,
       starts a newline, then returns the character to the calling program. The return value of the function  is
       the  character that was typed. If the read had to be aborted for some reason, EOF is returned instead. In
       the latter case, the application can call the previously documented gl_return_status(), to find out  what
       went  wrong.  This  could,  for  example, have been the reception of a signal, or the optional inactivity
       timer going off.

       If the user simply hits enter, the value of the defchar argument is substituted. This means that when the
       user hits either newline or return, the character specified in defchar, is displayed after the prompt, as
       though the user had typed it, as well as being returned to the calling application. If such a replacement
       is not important, simply pass '0 as the value of defchar.

       If the entered character is an unprintable character, it is displayed symbolically. For example, control-
       A is displayed as ^A, and characters beyond 127 are displayed in octal, preceded by a backslash.

       As with gl_get_line(), echoing of  the  entered  character  can  be  disabled  using  the  gl_echo_mode()
       function.

       If  the  calling  process  is  suspended while waiting for the user to type their response, the cursor is
       moved to the line following the prompt line, then when the process resumes, the  prompt  is  redisplayed,
       and gl_query_char() resumes waiting for the user to type a character.

       Note that in non-blocking server mode, (see gl_io_mode(3)), if an incomplete input line is in the process
       of being read when gl_query_char() is called, the partial input line is discarded, and  erased  from  the
       terminal,  before  the  new prompt is displayed. The next call to gl_get_line() will thus start editing a
       new line.

READING RAW CHARACTERS

       Whereas the gl_query_char() function visibly prompts the user for a character,  and  displays  what  they
       typed,  the  gl_read_char()  function reads a signal character from the user, without writing anything to
       the terminal, or perturbing any incompletely entered input line. This means that it  can  be  called  not
       only  from  between  calls  to  gl_get_line(),  but also from callback functions that the application has
       registered to be called by gl_get_line().

         int gl_read_char(GetLine *gl);

       On success, the return value of gl_read_char() is the  character  that  was  read.  On  failure,  EOF  is
       returned,  and  the  gl_return_status() function can be called to find out what went wrong. Possibilities
       include the optional inactivity timer going off, the receipt of a signal  that  is  configured  to  abort
       gl_get_line(), or terminal I/O blocking, when in non-blocking server-I/O mode.

       Beware  that  certain  keyboard keys, such as function keys, and cursor keys, usually generate at least 3
       characters each, so a single call to gl_read_char() won't be enough to identify such keystrokes.

CLEARING THE TERMINAL

       The calling program can clear the terminal by calling  gl_erase_terminal().  In  non-blocking  server-I/O
       mode,  this  function  also  arranges  for  the  current  input  line  to  be  redrawn  from scratch when
       gl_get_line() is next called.

         int gl_erase_terminal(GetLine *gl);

DISPLAYING TEXT DYNAMICALLY

       Between calls to gl_get_line(), the gl_display_text() function  provides  a  convenient  way  to  display
       paragraphs of text, left-justified and split over one or more terminal lines according to the constraints
       of the current width of the terminal. Examples of the use of this function  may  be  found  in  the  demo
       programs,  where  it  is  used  to  display introductions. In those examples the advanced use of optional
       prefixes, suffixes and filled lines to draw a box around the text is also illustrated.

         int gl_display_text(GetLine *gl, int indentation,
                             const char *prefix,
                             const char *suffix, int fill_char,
                             int def_width, int start,
                             const char *string);

       If gl isn't currently connected to a terminal,  for  example  if  the  output  of  a  program  that  uses
       gl_get_line()  is being piped to another program or redirected to a file, then the value of the def_width
       parameter is used as the terminal width.

       The indentation argument specifies the number of characters to use to indent each  line  of  output.  The
       fill_char argument specifies the character that will be used to perform this indentation.

       The  prefix argument can either be NULL, or be a string to place at the beginning of each new line (after
       any indentation).  Similarly, the suffix argument can either be NULL, or be a string to place at the  end
       of  each  line.  The suffix is placed flush against the right edge of the terminal, and any space between
       its first character and the last word on that line  is  filled  with  the  character  specified  via  the
       fill_char argument.  Normally the fill-character is a space.

       The  start  argument tells gl_display_text() how many characters have already been written to the current
       terminal line, and thus tells it the starting column index of the cursor.   Since  the  return  value  of
       gl_display_text()  is  the  ending column index of the cursor, by passing the return value of one call to
       the start argument of the next call, a paragraph that is broken between  more  than  one  string  can  be
       composed  by  calling  gl_display_text()  for each successive portion of the paragraph. Note that literal
       newline characters are necessary at the end of each paragraph to force a new line to be started.

       On error, gl_display_text() returns -1.

CALLBACK FUNCTION FACILITIES

       Unless otherwise stated, callback functions, such as tab completion callbacks and event callbacks  should
       not  call any functions in this module. The following functions, however, are designed specifically to be
       used by callback functions.

       Calling the gl_replace_prompt() function from a callback  tells  gl_get_line()  to  display  a  different
       prompt  when  the  callback returns. Except in non-blocking server mode, it has no effect if used between
       calls to gl_get_line(). In non-blocking server mode (see the gl_io_mode(3) man page,  when  used  between
       two  calls to gl_get_line() that are operating on the same input line, the current input line will be re-
       drawn with the new prompt on the following call to gl_get_line().

         void gl_replace_prompt(GetLine *gl, const char *prompt);

INTERNATIONAL CHARACTER SETS

       Since libtecla version 1.4.0, gl_get_line() has been 8-bit clean. This means that  all  8-bit  characters
       that  are  printable in the user's current locale are now displayed verbatim and included in the returned
       input line.  Assuming that the calling program correctly contains a call like the following,

         setlocale(LC_CTYPE, "");

       then the current locale is determined by the first of the environment  variables  LC_CTYPE,  LC_ALL,  and
       LANG,  that  is  found  to  contain  a  valid locale name. If none of these variables are defined, or the
       program neglects to call setlocale, then the default C locale is used, which is US 7-bit ASCII.  On  most
       unix-like platforms, you can get a list of valid locales by typing the command:

         locale -a

       at  the  shell  prompt. Further documentation on how the user can make use of this to enter international
       characters can be found in the tecla(7) man page.

THREAD SAFETY

       In a multi-threaded program, you should use the libtecla_r.a version of the library. This uses  reentrant
       versions  of  system functions, where available. Unfortunately neither terminfo nor termcap were designed
       to be reentrant, so you can't safely use the functions of the getline module in multiple threads (you can
       use  the  separate  file-expansion and word-completion modules in multiple threads, see the corresponding
       man pages for details). However due to  the  use  of  POSIX  reentrant  functions  for  looking  up  home
       directories etc, it is safe to use this module from a single thread of a multi-threaded program, provided
       that your other threads don't use any termcap or terminfo functions.

FILES

       libtecla.a      -    The tecla library
       libtecla.h      -    The tecla header file.
       ~/.teclarc      -    The personal tecla customization file.

SEE ALSO

       libtecla(3), gl_io_mode(3), tecla(7), ef_expand_file(3),
       cpl_complete_word(3), pca_lookup_file(3)

AUTHOR

       Martin Shepherd  (mcs@astro.caltech.edu)

                                                                                                  gl_get_line(3)