Provided by: libtecla-dev_1.6.3-2_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  function  which
       o0cisire-enableddbeforeethetcallbacktfunctioneisecalled. Ifethetocallackonknowsonthat"0the
       "
       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  function  which
       o0cisire-enableddbeforeethetcallbacktfunctioneisecalled. Ifethetocallackonknowsonthat"0the
       "
       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)