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       gl_get_line,    new_GetLine,    del_GetLine,   gl_customize_completion,
       gl_change_terminal, gl_configure_getline, gl_load_history, gl_save_his‐
       tory,   gl_group_history,   gl_show_history,  gl_watch_fd,  gl_inactiv‐
       ity_timeout,  gl_terminal_size,	gl_set_term_size,   gl_resize_history,
       gl_limit_history,  gl_clear_history,  gl_toggle_history, gl_lookup_his‐
       tory,  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_regis‐
       ter_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

       cc [ flag... ] file... -ltecla [ library... ]
       #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);

       int gl_erase_terminal(GetLine *gl);

       The gl_get_line() function is part of the libtecla(3LIB)	 library.   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  con‐
       figuration options can be found on the tecla(5) manual page.

   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);
	     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()	 func‐
       tion  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_Get‐
       Line(), 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  new_GetLine()  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 by  the
       linelen	argument, and the number of bytes to allocate for storing his‐
       tory 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 descrip‐
       tion  of the gl_limit_history() function. If you do not 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.

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

       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
       null-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, prompts can contain directives to do under‐
       lining, 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 with the start_line argument. You can
       then specify which character of this line the cursor is initially posi‐
       tioned  over  by 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
       do  not	want  to  preload  the line in this manner, send start_line as
       NULL, and set start_pos to -1.

       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
       freed  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(3C). When stdin is not connected  to  a  terminal,	 gl_get_line()
       simply calls fgets().

   The Return Status Of gl_get_line()
       The gl_get_line() function has two possible return values: a pointer to
       the completed input line, or NULL. Additional  information  about  what
       caused  gl_get_line()  to  return is available both by inspecting errno
       and by calling the gl_return_status() function.

       The  following  are  the	 possible  enumerated	values	 returned   by

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

		      The gl_get_line() function 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

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

		      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.

		      An  application  I/O  callback returned GLFD_ABORT. Ssee

		      End of file reached. This can happen when input is  com‐
		      ing  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.

		      An  unexpected error caused gl_get_line() to abort (con‐
		      sult errno and/or gl_error_message() for details.

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

       The return value of gl_error_message() is a pointer to the message that
       occurred.  If  the  buff	 argument is NULL, this will be a pointer to a
       buffer within gl whose 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' termina‐
       tor,  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	 will not fit in the provided buffer, it will be trun‐
       cated to fit.

   Optional Prompt Formatting
       Whereas by default the prompt string that you specify is displayed lit‐
       erally  without any special interpretation of the characters within it,
       the gl_prompt_style() function can be used to enable  optional  format‐
       ting directives within the prompt.

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

			    In this style, the formatting directives described
			    below, when included in prompt strings, are inter‐
			    preted as follows:

				  Display subsequent characters	 with  a  bold

				  Stop	displaying  characters	with  the bold

				  Make subsequent characters flash.

				  Turn off flashing characters.

				  Underline subsequent characters.

				  Stop underlining characters.

				  Switch to a pale (half brightness) font.

				  Stop using the pale font.

				  Highlight subsequent characters (also	 known
				  as standout mode).

				  Stop highlighting characters.

				  Turn on reverse video.

				  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 does not 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.

			    In this style, the prompt string is printed liter‐
			    ally. This is the default style.

   Alternate Configuration Sources
       By default users	 have  the  option  of	configuring  the  behavior  of
       gl_get_line()  with  a configuration file called .teclarc in their home
       directories. The fact that all applications share this same  configura‐
       tion  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  par‐
       ticularly  true	of  embedded  software, where there's no filesystem to
       read a configuration file from, and also in applications where a	 radi‐
       cally  different	 choice	 of  keybindings is needed to emulate a legacy
       keyboard interface. To cater for such cases, the gl_configure_getline()
       function allows the application to control where configuration informa‐
       tion is read from.

       The gl_configure_getline() function 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 configurations 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  configura‐
       tion file. If user_file != NULL then it is interpreted as the full path
       name of a user-specific configuration file,  such  as  ~/.teclarc.  For
       example, in the 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(1) 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 sys‐
       tem-wide	 configuration	commands  from	 an   optional	 file	called
       /usr/share/myapp/teclarc,  then	finally reads user-specific configura‐
       tion commands from an optional .teclarc file in the user's home	direc‐
       tory.   Note that the arguments are listed in ascending order of prior‐
       ity, with the contents of app_string being potentially  over  riden  by
       commands	 in app_file, and commands in app_file potentially being over‐
       riden 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 file names specified with 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 config‐
       uration files be re-read.

       Individual key sequences can  also  be  bound  and  unbound  using  the
       gl_bind_keyseq()	 function.  The origin argument specifies the priority
       of the binding, according to whom it is being established for, and must
       be one of the following two values.

		      The user requested this key-binding.

		      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 with either another call to this function, or a call to gl_con‐

       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 with a
       call to the gl_customize_completion() function.

       The data argument provides a way for your  application  to  pass	 arbi‐
       trary,  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 on the cpl_complete_word(3TECLA)  man‐
       ual page.

       The callback function is responsible for looking backwards in the input
       line 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 wants to provide filename completion
       in  addition  to	 its  own  specific  completions, it has the option of
       itself calling the builtin filename completion callback. This  also  is
       documented on the cpl_complete_word(3TECLA) manual page.

       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. The input line will be updated  to  display
       the  completion, together with any contiuation suffix up to the newline
       character, and gl_get_line() will return this input line.

       If 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 notify 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_comple‐
       tion_action() function.

       The  data  and  match_fn	 arguments  are	 as  described on the cpl_com‐
       plete_word(3TECLA) manual page, and specify the callback function  that
       should be invoked to identify possible completions. The list_only argu‐
       ment determines whether the action that is being defined should attempt
       to  complete  the word as far as possible in the input line before dis‐
       playing 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	 func‐
       tion  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	 key  sequence
       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, you should‐
       call  gl_completion_action()  to	 install  a given action for the first
       time 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	 will  not  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
       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.

       The  gl_register_action()  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  wants  to
       have  passed  to	 the  action  function,	 fn, whenever that function is

       The action function, fn, should be declared  using  the	GL_ACTION_FN()
       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 enter‐
       ing using the digit-argument action, before invoking the action. If the
       user  does  not	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	 argu‐
       ment.  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 because the
       rules dictated by various modes (such as vi mode versus emacs mode, no-
       echo  mode, and insert mode versus overstrike mode) 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 poten‐
       tial solution to this dilemma 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 restor‐
       ing the normal mapping of \n to \r\n, and, when in server mode, restor‐
       ing the normal blocking form of terminal I/O. Having called this	 func‐
       tion, the action function can read from and write to the terminal with‐
       out the fear of creating a mess. It is not  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 proceed.

		       Cause gl_get_line() to return NULL.

		       Cause gl_get_line() to return the completed input line

		       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-sequence. 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 appli‐
       cation and subsequently restore them when you next start	 the  applica‐
       tion,  the  gl_save_history()  and gl_load_history() functions are pro‐

       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, additional information about it, such as
       its nesting level and when it was entered by the user, is recorded as a
       comment	preceding the line in the history file. Writing this as a com‐
       ment 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  argument 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  fuctions return non-zero on error, after writing an error message
       to stderr. Note that gl_load_history() does not consider the  non-exis‐
       tence of a file to be an error.

   Multiple History Lists
       If your application uses a single GetLine object for entering many dif‐
       ferent types of input lines, you might want  gl_get_line()  to  distin‐
       guish 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().

       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 pro‐
       gram  invocations,  so you should choose fixed identifiers for the dif‐
       ferent 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(). This
       function 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 his‐
       tory groups are	displayed.  Otherwise  only  those  of	the  currently
       selected	 history group are displayed. The format string argument, fmt,
       determines how the line is displayed. This can contain arbitrary	 char‐
       acters  which are written verbatim, interleaved with any of the follow‐
       ing format directives:

	     The date on which the line was originally entered, formatted like

	     The  time	of  day	 when  the  line  was  entered, formatted like

	     The sequential entry number of the line in the history buffer.

	     The number of the history group which the line belongs to.

	     A literal % character.

	     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

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

       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  succes‐
       sively 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.  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.	There‐
       fore  you should make a private copy of this string if you need to keep

   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  applica‐
       tions,  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.

       If this	function  is  called  with  its	 enable	 argument  set	to  0,
       gl_get_line()  will  not	 automatically	archive	 subsequently  entered
       lines.  Automatic archiving can be reenabled 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.

       The  line  argument specifies the line to be added to the history list.
       This must be a normal '\0 ' 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	termi‐
       nated  by  the '\0 ' terminator. If the line is longer than the maximum
       input line length that was specified when new_GetLine() was called,  it
       will be truncated to the actual gl_get_line() line length when the line
       is recalled.

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

		 One of the arguments passed to gl_append_history() was NULL.

		 The  specified line was longer than the allocated size of the
		 history buffer (as specified when new_GetLine() was  called),
		 so it could not be archived.

       A  textual description of the error can optionally be obtained by call‐
       ing 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 lit‐
       tle 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	origi‐
       nally  specified	 in  the call to new_GetLine(), you can do so with the
       gl_resize_history() function.

       The histlen argument specifies the new size in bytes, and if you	 spec‐
       ify 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 20 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
       accomodate 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.

       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()

       The  all_groups	argument tells the function whether to delete just the
       lines associated with the  current  history  group  (see	 gl_group_his‐
       tory()) 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.

       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-bind‐
       ings 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.  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. The return values are recorded in the	 vari‐
       able  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. Oth‐
       erwise 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.

       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.

       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 with 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 termi‐
       nal.   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 do not 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(3C) function.

   External Event Handling
       By default, gl_get_line() does not 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.

	   o	  Use the functions described in the gl_io_mode(3TECLA) manual
		  page	to switch gl_get_line() into non-blocking server mode.
		  In this mode, gl_get_line() becomes a	 non-blocking,	incre‐
		  mental  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().

	   o	  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 or pipes, 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. If this returns non-zero,  then  it
       means  that either your arguments are invalid, or that this facility is
       not supported on the host system.

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

		      Watch for the arrival of data to be read.

		      Watch for the ability to write to	 the  file  descriptor
		      without blocking.

		      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	activ‐
       ity  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	 call‐
       back  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.

			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 mean‐
			ingful value  when  gl_get_line()  returns  NULL,  the
			callback function should set errno appropriately.

			Redraw	the  input  line   then	 continue  waiting for
			input. Return this if your callback wrote to the  ter‐

			Continue  to  wait  for	 input,	 without redrawing the

       Note that before calling the callback, gl_get_line() blocks  most  sig‐
       nals  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.

       Your  callback  should not try to read from the terminal, which is left
       in raw mode as far as input is concerned. You can write to the terminal
       as  usual,  since  features  like  conversion  of  newline to carriage-
       return/linefeed are re-enabled while the callback is running.  If  your
       callback	 function does write to the terminal, be sure to output a new‐
       line first, and when your callback returns, tell gl_get_line() that the
       input  line  needs  to be redrawn, by returning the GLFD_REFRESH status

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

   Setting An Inactivity Timeout
       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 sub‐
       sequent calls to gl_watch_fd().

       The timeout is specified in the form of an integral number  of  seconds
       and  an	integral  number of nanoseconds, specified by the sec and nsec
       arguments, respectively. Subsequently, whenever no activity is seen for
       this  time  period,  the function specified by the callback argument is
       called.	The data argument of gl_inactivity_timeout() is passed to this
       callback	 function whenever it is invoked, and can thus be used to pass
       arbitrary application-specific information to the callback. The follow‐
       ing  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.

			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.

			Redraw	the  input  line,  then	 continue  waiting for
			input. You should return this value if	your  callback
			wrote to the terminal.

			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(3TECLA)),
			gl_get_line() acts 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

       Note  that  before calling the callback, gl_get_line() blocks most sig‐
       nals 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.

       Your callback should not try to read from the terminal, which  is  left
       in  raw mode as far as input is concerned. You can however write to the
       terminal as usual, since features like conversion of  newline  to  car‐
       riage-return/linefeed  are re-enabled while the callback is running. If
       your callback function does write to the terminal, be sure to output  a
       newline	first, and when your callback returns, tell gl_get_line() that
       the input line needs to be redrawn, by returning the GLTO_REFRESH  sta‐
       tus code.

       Finally,	 note that although the timeout arguments include a nanosecond
       component, few computer clocks  presently  have	resolutions  that  are
       finer  than a few milliseconds, so asking for less than a few millisec‐
       onds is equivalent to requesting zero seconds on many systems. If  this
       would  be  a  problem,  you  should  base your timeout selection on the
       actual  resolution  of  the  host  clock	 (for  example,	  by   calling

       To  turn off timeouts, simply call gl_inactivity_timeout() with a call‐
       back 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 that would by default termi‐
       nate the process, since the terminal needs to be restored to  a	usable
       state  before this happens. This section describes the signals that are
       trapped by default and how gl_get_line()	 responds  to  them.  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 call‐
       ing application's signal handlers to handle it, then,  if  the  process
       still exists, returns NULL and sets errno as specified below.

		  This	signal is generated both by the keyboard interrupt key
		  (usually ^C), and the keyboard break key. The errno value is

		  This	signal	is  generated  when  the  controlling terminal
		  exits. The errno value is ENOTTY.

		  This signal is generated when a program attempts to write to
		  a  pipe  whose  remote end is not 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. The errno value is EPIPE.

		  This signal is generated by the keyboard quit	 key  (usually
		  ^\fR). The errno value is EINTR.

		  This	signal is generated by the standard C, abort function.
		  By default it both terminates the process  and  generates  a
		  core dump. The errno value is EINTR.

		  This	is the default signal that the UNIX kill command sends
		  to processes. The errno value is 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  does not 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  gl_last_signal()  function.
       This  returns the numeric code (for example, 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 accomodate the new size, then returns
       to waiting for keyboard input from the user. Unlike other signals, this
       signal is not 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.

		    This  signal  is  generated	 when  a  suspended process is

		    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() does not trap it by

		    This signal is generated when a power failure occurs (pre‐
		    sumably when the system is on a UPS).

		    This signal is generated when a timer expires.

		    An application specific signal.

		    Another application specific signal.

		    This signal is generated when a virtual timer expires. See

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

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

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

		    This signal is generated if the program attempts  to  read
		    from  the  terminal	 while	the  program is running in the

		    This signal is generated if the program attempts to	 write
		    to	the terminal while the program is running in the back‐

       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 cannot 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-con‐
       trol shells usually reset the terminal settings when a  process	relin‐
       quishes	the controlling terminal, so this is only a problem with older

   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 do not 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().

       The  signo  argument  is the number of the signal (for example, SIGINT)
       that you want to have ignored. If the specified signal is not 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.

       The  signo  argument  is the number of the signal that you want to have
       trapped. The flags argument is a set of flags that determine the	 envi‐
       ronment 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. The 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

			   Restore  the caller's signal environment while han‐
			   dling the signal.

			   Restore the caller's terminal settings  while  han‐
			   dling the signal.

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

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

			   Normally, if	 the  calling  program	has  a	signal
			   blocked  (see  sigprocmask(2)),  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().

			   If this flag is included, the signal	 will  not  be
			   forwarded to the signal handler of the calling pro‐

       Two commonly useful flag combinations are also enumerated as follows:



       If your signal handler, or the default system signal handler  for  this
       signal,	if you have not overridden it, never either writes to the ter‐
       minal, nor suspends or terminates the calling  program,	then  you  can
       safely set the flags argument to 0.

	   o	  The  cursor  does  not  get  left in the middle of the input

	   o	  So that the user can type in input and have it echoed.

	   o	  So that you do not 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 does not move the cursor. If your signal handler does not  read
       or  write  anything  to the terminal, the user will not 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 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 does not do any
       harm, but it looks a bit ugly, which is why the GL_SUSPEND_INPUT combi‐
       nation is better if you know that you are always going to  be  writting
       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:

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

		       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.

		       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 want 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	condi‐
       tions.  In gl_get_line() a lot of care has been taken to allow applica‐
       tions 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 is not
       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  hap‐
       pens  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  will  not  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() func‐
		  tion, and specifying the GLS_UNBLOCK attribute of  the  sig‐
		  nal, or globally by calling the gl_catch_blocked() function.
		  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 conjunc‐
		  tion with  the  gl_list_signals()  function.	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(2).

	   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	 func‐
       tions,  such as sigsetjmp(3C) and sigsuspend(2), and in particular, the
       former of these two functions can be  used  in  conjunction  with  sig‐
       longjmp(3C)  to	implement  race-condition  free signal handling around
       other long-running system calls. The gl_get_line() function manages  to
       reliably	 trap  signals	around	calls  to  functions  like read(2) and
       select(3C) without race conditions.

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

       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 savemask argument.

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

	   1.	  It uses the POSIX sigaction(2) function to register a tempo‐
		  rary signal handler to all of the signals that it is config‐
		  ured to catch. This signal handler does two things.

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

	       b.     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 config‐
	   ured	 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 do not tread on each other's toes.

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

	   3.	  It  then  calls  the read() or select() function to wait for
		  keyboard input.

	   4.	  If this function returns (that is, no signal	is  received),
		  gl_get_line()	 blocks	 delivery  of  the signals of interest

	   5.	  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 execut‐
       ing. When this happens, gl_get_line() does the following.

       First,  note  that  when	 a  call to siglongjmp() causes sigsetjmp() to
       return, provided that the savemask argument  of	sigsetjmp()  was  non-
       zero,  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(3C), and is the essential
       ingredient that makes it possible to avoid signal handling race	condi‐
       tions.  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

	   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	impor‐
		  tant	for  signals  that  suspend  or terminate the process,
		  since otherwise the terminal would be left  in  an  unusable

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

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

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

	   5.	  If  the  signal handler returns (that is, it does not termi‐
		  nate the process),  gl_get_line()  blocks  delivery  of  the
		  above signal again.

	   6.	  It  then  undoes  any	 actions performed in the first of the
		  above steps and redisplays the line, if the signal  configu‐
		  ration calls for this.

	   7.	  gl_get_line()	 then  either resumes trying to read a charac‐
		  ter, 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 SIG‐
       WINCH 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 is not  available,  at  startup
       new_GetLine()  first  looks for the LINES and COLUMNS environment vari‐
       ables. If these are not 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) are not 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.

       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 sup‐
       port 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 accomodate 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 is not available. Beware that the terminal size	 will  not  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.

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

       The def_ncolumn and def_nline arguments specify the default  number  of
       terminal columns and lines to use if the terminal size cannot be deter‐
       mined by 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. Further‐
       more, such text should not be recorded in the history list, since some‐
       body 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().

       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	has not been turned off with a call to gl_tog‐
       gle_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 set‐
       ting  through  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  comple‐
       tions 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.

       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 char‐
       acter, 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_sta‐
       tus(), 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 '\n' 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, if an incomplete input  line  is
       in  the	process of being read when gl_query_char() is called, the par‐
       tial 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().

       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() func‐
       tion 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 three characters each, so a single call
       to gl_read_char() will not be enough to identify such keystrokes.

   Clearing The Terminal
       The  calling  program can clear the terminal by calling gl_erase_termi‐
       nal(). 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.

   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	intro‐
       ductions.  In  those  examples  the advanced use	 of optional prefixes,
       suffixes and filled lines to draw a box around the text is also	illus‐

       If gl is not currently connected to a terminal, for example if the out‐
       put of a program that uses gl_get_line() is being piped to another pro‐
       gram 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 ouput. The fill_char argument specifies the charac‐
       ter that will be used to perform this indentation.

       The prefix argument can be either NULL or a  string  to	place  at  the
       beginning of each new line (after any indentation). Similarly, the suf‐
       fix argument can be either NULL or a string to place at the end of each
       line.   The suffix is placed flush against the right edge of the termi‐
       nal, and any space between its first character and  the	last  word  on
       that line is filled with the character specified by the fill_char argu‐
       ment. 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	 para‐
       graph.	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, 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 fol‐
       lowing call to gl_get_line().

   International Character Sets
       Since libtecla(3LIB) 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(3C), 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(5)
       man page.

   Thread Safety
       Unfortunately neither terminfo nor termcap were designed	 to  be	 reen‐
       trant,  so you cannot safely use the functions of the getline module in
       multiple threads (you can use the separate file-expansion and word-com‐
       pletion	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, it is safe to use this module from a sin‐
       gle thread of  a	 multi-threaded	 program,  provided  that  your	 other
       threads do not use any termcap or terminfo functions.

       See attributes(5) for descriptions of the following attributes:

       │Interface Stability │ Committed	      │
       │MT-Level	    │ MT-Safe	      │

       cpl_complete_word(3TECLA),  ef_expand_file(3TECLA), gl_io_mode(3TECLA),
       libtecla(3LIB), pca_lookup_file(3TECLA), attributes(5), tecla(5)

				 Sep 10, 2013		   GL_GET_LINE(3TECLA)

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