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.TH gl_get_line @FUNC_MANEXT@
.SH 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
.SH SYNOPSIS
.nf
#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);

.fi

.SH DESCRIPTION

The \f3gl_get_line()\f1 function is part of the tecla library (see the
\f3libtecla(@LIBR_MANEXT@)\f1 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 \f3tcsh\f1 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 \f3tecla(@MISC_MANEXT@)\f1 man page. This man page
concerns itself with documentation for programmers interested in using
this library in their application.
.sp
.SH AN EXAMPLE

The following shows a complete example of how to use the
\f3gl_get_line()\f1 function to get input from the user:

.nf
  #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;
  }
.fi
.sp
In the example, first the resources needed by the \f3gl_get_line()\f1 function
are created by calling \f3new_GetLine()\f1. This allocates the memory used in
subsequent calls to the \f3gl_get_line()\f1 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 \f3exit\f1. Then
finally the resources that were allocated by \f3new_GetLine()\f1, are returned
to the system by calling \f3del_GetLine()\f1. Note the use of the \f3NULL\f1
return value of \f3del_GetLine()\f1 to make \f3gl\f1 \f3NULL\f1. This is a
safety precaution. If the program subsequently attempts to pass \f3gl\f1 to
\f3gl_get_line()\f1, said function will complain, and return an error, instead of
attempting to use the deleted resource object.

.sp
.SH THE FUNCTIONS USED IN THE EXAMPLE
The descriptions of the functions used in the example are as follows:
.sp
.nf
  GetLine *new_GetLine(size_t linelen, size_t histlen)
.fi
.sp
This function creates the resources used by the \f3gl_get_line()\f1
function and returns an opaque pointer to the object that contains
them.  The maximum length of an input line is specified via the
\f3linelen\f1 argument, and the number of bytes to allocate for
storing history lines is set by the \f3histlen\f1 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 \f3gl_limit_history()\f1 function described later. If
you don't want history at all, specify \f3histlen\f1 as zero, and no
history buffer will be allocated.
.sp
On error, a message is printed to \f3stderr\f1 and \f3NULL\f1 is returned.
.sp
.nf
  GetLine *del_GetLine(GetLine *gl)
.fi
.sp
This function deletes the resources that were returned by a previous
call to \f3new_GetLine()\f1. It always returns \f3NULL\f1 (ie a
deleted object). It does nothing if the \f3gl\f1 argument is
\f3NULL\f1.
.sp
.nf
  char *gl_get_line(GetLine *gl, const char *prompt,
                   const char *start_line, int start_pos);
.fi
.sp
The \f3gl_get_line()\f1 function can be called any number of
times to read input from the user. The \f3gl\f1 argument
must have been previously returned by a call to
\f3new_GetLine()\f1. The \f3prompt\f1 argument should be a
normal \f3NUL\f1 terminated string, specifying the prompt to
present the user with. By default prompts are displayed
literally, but if enabled with the \f3gl_prompt_style()\f1
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 \f3start_line\f1
argument. You can then specify which character of this line the cursor
is initially positioned over, using the \f3start_pos\f1 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 \f3start_line\f1 as \f3NULL\f1, and set \f3start_pos\f1 to
-1. Note that the line pointer returned by one call to
\f3gl_get_line()\f1 can be passed back to the next call to
\f3gl_get_line()\f1 via the \f3start_line\f1. 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 \f3gl_get_line()\f1 function returns a pointer to the line entered
by the user, or \f3NULL\f1 on error or at the end of the input. The
returned pointer is part of the specified \f3gl\f1 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 \f3gl_get_line()\f1 again to read the rest of the line. Note that
this behavior makes \f3gl_get_line()\f1 similar to \f3fgets()\f1.  In
fact when \f3stdin\f1 isn't connected to a terminal,\f3gl_get_line()\f1
just calls \f3fgets()\f1.

.SH THE RETURN STATUS OF GL_GET_LINE

As described above, the \f3gl_get_line()\f1 function has two possible
return values; a pointer to the completed input line, or
\f3NULL\f1. Extra information about what caused \f3gl_get_line()\f1 to
return is available both by inspecting \f3errno\f1, and by calling the
\f3gl_return_status()\f1 function.

.sp
.nf
  GlReturnStatus gl_return_status(GetLine *gl);
.fi
.sp

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

.sp
.nf
  GLR_NEWLINE     -  The last call to \f3gl_get_line()\f1
                     successfully returned a completed
                     input line.

  GLR_BLOCKED     -  \f3gl_get_line()\f1 was in non-blocking
                     server mode, and returned early to
                     avoid blocking the process while
                     waiting for terminal I/O. The
                     \f3gl_pending_io()\f1 function can be
                     used to see what type of I/O
                     \f3gl_get_line()\f1 was waiting for.
                     (see the \f3gl_io_mode(@FUNC_MANEXT@)\f1 man page
                     for details).

  GLR_SIGNAL      -  A signal was caught by
                     \f3gl_get_line()\f1 that had an
                     after-signal disposition of
                     \f3GLS_ABORT\f1 (See \f3gl_trap_signal()\f1).

  GLR_TIMEOUT     -  The inactivity timer expired while
                     \f3gl_get_line()\f1 was waiting for
                     input, and the timeout callback
                     function returned \f3GLTO_ABORT\f1.
                     See \f3gl_inactivity_timeout()\f1 for
                     information about timeouts.

  GLR_FDABORT     -  An application I/O callack returned
                     \f3GLFD_ABORT\f1 (see \f3gl_watch_fd()\f1).

  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
                     \f3list-or-eof\f1 or \f3del-char-or-list-or-eof\f1
                     actions at the start of a new line.

  GLR_ERROR       -  An unexpected error caused
                     \f3gl_get_line()\f1 to abort (consult
                     \f3errno\f1 and/or
                     \f3gl_error_message()\f1 for details.
.fi
.sp

When \f3gl_return_status()\f1 returns \f3GLR_ERROR\f1, and the
value of \f3errno\f1 isn't sufficient to explain what
happened, you can use the \f3gl_error_message()\f1 function
to request a description of the last error that occurred.

.sp
.nf
  const char *gl_error_message(GetLine *gl, char *buff,
                               size_t n);
.fi
.sp

The return value is a pointer to the message that
occurred. If the \f3buff\f1 argument is \f3NULL\f1, this
will be a pointer to a buffer within \f3gl\f1, who's value
will probably change on the next call to any function
associated with \f3gl_get_line()\f1. Otherwise, if a
non-\f3NULL\f1 \f3buff\f1 argument is provided, the error
message, including a \f3'\\0'\f1 terminator, will be written
within the first \f3n\f1 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.

.SH 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 \f3gl_prompt_style()\f1
function can be used to enable optional formatting
directives within the prompt.
.sp
.nf
  void gl_prompt_style(GetLine *gl, GlPromptStyle style);
.fi
.sp
The \f3style\f1 argument, which specifies the formatting
style, can take any of the following values:
.sp
.nf
  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 \f3"%UOK%u$ "\f1 would
                        display the prompt \f3"OK$ "\f1,
                        but with the \f3OK\f1 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.
.fi

.SH ALTERNATE CONFIGURATION SOURCES

As mentioned above, by default users have the option of configuring
the behavior of \f3gl_get_line()\f1 via a configuration file called
\f3\&.teclarc\f1 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.

.sp
.nf
  int gl_configure_getline(GetLine *gl,
                           const char *app_string,
                           const char *app_file,
                           const char *user_file);
.fi
.sp

It allows the configuration commands that would normally be read from
a user's \f3~/.teclarc\f1 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 \f3gl_get_line()\f1, the default behavior of
reading \f3~/.teclarc\f1 on the first call to \f3gl_get_line()\f1 is
disabled, so all configuration must be achieved using the
configuration sources specified with this function.

If \f3app_string != NULL\f1, 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 \f3app_file !=
NULL\f1 then it is interpreted as the full pathname of an
application-specific configuration file. If \f3user_file != NULL\f1
then it is interpreted as the full pathname of a user-specific
configuration file, such as \f3~/.teclarc\f1. For example, in the
following call,

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

the \f3app_string\f1 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
\f3/usr/share/myapp/teclarc\f1, then finally reads user-specific
configuration commands from an optional \f3\&.teclarc\f1 file in the
user's home directory. Note that the arguments are listed in ascending
order of priority, with the contents of \f3app_string\f1 being
potentially overridden by commands in \f3app_file\f1, and commands in
\f3app_file\f1 potentially being overridden by commands in
\f3user_file\f1.
.sp
You can call this function as many times as needed, the results being
cumulative, but note that copies of any filenames specified via the
\f3app_file\f1 and \f3user_file\f1 arguments are recorded internally
for subsequent use by the \f3read-init-files\f1 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.
.sp
Individual key sequences can also be bound and unbound using the
\f3gl_bind_keyseq()\f1 function.

.sp
.nf
  int gl_bind_keyseq(GetLine *gl, GlKeyOrigin origin,
                     const char *keyseq,
                     const char *action);
.fi
.sp

The \f3origin\f1 argument specifies the priority of the binding,
according to who it is being established for, and must be one of
the following two values.
.sp
.nf
  GL_USER_KEY   -   The user requested this key-binding.
  GL_APP_KEY    -   This is a default binding set by the
                    application.
.fi
.sp
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
\f3gl_configure_getline()\f1.

The \f3keyseq\f1 argument specifies the key-sequence to be bound or
unbound, and is expressed in the same way as in a \f3~/.teclarc\f1
configuration file. The \f3action\f1 argument must either be a string
containing the name of the action to bind the key-sequence to, or it
must be \f3NULL\f1 or "" to unbind the key-sequence.

.SH 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 \f3gl_customize_completion()\f1 function.
.sp
.nf
  int gl_customize_completion(GetLine *gl, void *data,
                              CplMatchFn *match_fn);
.fi
.sp
The \f3data\f1 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 \f3match_fn\f1 argument
specifies the callback function to be called. The \f3CplMatchFn\f1
function type is defined in \f3libtecla.h\f1, as is a
\f3CPL_MATCH_FN()\f1 macro that you can use to declare and prototype
callback functions. The declaration and responsibilities of callback
functions are described in depth in the \f1cpl_complete_word(@FUNC_MANEXT@)\f1 man
page.
.sp
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
\f3WordCompletion\f1 object that is passed to it as an argument, by
calling the \f3cpl_add_completion()\f1 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
\f3cpl_complete_word(@FUNC_MANEXT@)\f1 man page.
.sp
Note that if you would like \f3gl_get_line()\f1 to return the current
input line when a successful completion is been made, you can arrange
this when you call \f3cpl_add_completion()\f1, 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
\f3gl_get_line()\f1 will return this input line.
.sp

If, for some reason, your callback function needs to write something
to the terminal, it must call \f3gl_normal_io()\f1 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
\f3gl_get_line()\f1 that the input line will need to be redrawn when
the callback returns.

.SH ADDING COMPLETION ACTIONS

In the previous section the ability to customize the behavior of the
only default completion action, \f3complete-word\f1, 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
\f3gl_completion_action()\f1 function.

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

The \f3data\f1 and \f3match_fn\f1 arguments are as described
in the \f3cpl_complete_word\f1 man page, and specify the
callback function that should be invoked to identify
possible completions.  The \f3list_only\f1 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 \f30\f1, and the
latter by specifying a value of \f31\f1. The \f3name\f1
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 \f3keyseq\f1 argument specifies
the default key-sequence to bind the action to. If this is
\f3NULL\f1, 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 \f3gl_completion_action()\f1 to
install a given action for the first time, you should do
this between calling \f3new_GetLine()\f1 and the first call
to \f3gl_get_line()\f1.  Otherwise, when the user's
configuration file is read on the first call to
\f3gl_get_line()\f1, 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 \f3gl_customize_completion()\f1, if your callback
function, for some reason, needs to write anything to the terminal, it
must call \f3gl_normal_io()\f1 before doing so.

.SH 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 \f3gl_register_action()\f1 function is provided.

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

This function lets the application register an external function,
\f3fn\f1, that will thereafter be called whenever either the specified
key-sequence, \f3keyseq\f1, is entered by the user, or the user enters
any other key-sequence that the user subsequently binds to the
specified action name, \f3name\f1, in their configuration file. The
\f3data\f1 argument can be a pointer to anything that the application
wishes to have passed to the action function, \f3fn\f1, whenever that
function is invoked.

The action function, \f3fn\f1, should be declared using the following
macro, which is defined in \f3libtecla.h\f1.

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

The \f3gl\f1 and \f3data\f1 arguments are those that were previously
passed to \f3gl_register_action()\f1 when the action function was
registered. The \f3count\f1 argument is a numeric argument which the
user has the option of entering using the \f3digit-argument\f1 action,
before invoking the action. If the user doesn't enter a number, then
the \f3count\f1 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 \f3count\f1 argument, or use its value for a
different purpose.

A copy of the current input line is passed in the read-only \f3line\f1
argument. The current cursor position within this string is given by
the index contained in the \f3curpos\f1 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 \f3gl_get_line()\f1. 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 \f3gl_normal_io()\f1 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 \f3\\n\f1 to \f3\\r\\n\f1, 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
\f3gl_get_line()\f1 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.

.sp
.nf
  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;
  }
.fi
.sp

Action functions must return one of the following values, to tell
\f3gl_get_line()\f1 how to procede.

.sp
.nf
  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.
.fi
.sp

Note that the \f3name\f1 argument of \f3gl_register_action()\f1
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 \f3gl_register_action()\f1 between calling \f3new_GetLine()\f1
and the first call to \f3gl_get_line()\f1.

.SH 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.

.sp
.nf
 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);
.fi
.sp

The \f3filename\f1 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".
.sp
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 \f3comment\f1 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 \f3gl_load_history()\f1 that you used
when you called \f3gl_save_history()\f1 to write the history file.
.sp
The \f3max_lines\f1 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.
.sp
Both functions return non-zero on error, after writing an error message
to stderr. Note that \f3gl_load_history()\f1 does not consider the
non-existence of a file to be an error.

.SH MULTIPLE HISTORY LISTS

If your application uses a single \f3GetLine\f1 object for entering
many different types of input lines, you may wish \f3gl_get_line()\f1
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, \f3gl_get_line()\f1 marks lines being recorded in the
history list with an integer identifier chosen by the application.
Initially this identifier is set to \f10\f3 by \f3new_GetLine()\f1,
but it can be changed subsequently by calling
\f3gl_group_history()\f1.

.sp
.nf
  int gl_group_history(GetLine *gl, unsigned id);
.fi
.sp

The integer identifier \f3id\f1 can be any number chosen by the
application, but note that \f3gl_save_history()\f1 and
\f3gl_load_history()\f1 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.
.sp
Whenever \f3gl_get_line()\f1 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.

.SH DISPLAYING HISTORY

The history list can be displayed by calling \f3gl_show_history()\f1.

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

This displays the current contents of the history list to the stdio
output stream \f3fp\f1. If the \f3max_lines\f1 argument is greater
than or equal to zero, then no more than this number of the most
recent lines will be displayed. If the \f3all_groups\f1 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, \f3fmt\f1, determines how the line is
displayed. This can contain arbitrary characters which are written
verbatim, interleaved with any of the following format directives:

.nf
  %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.
.fi

Thus a format string like \f3"%D %T  %H\n"\f1 would output something like:

.nf
  2001-11-20 10:23:34  Hello world
.fi

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

.SH LOOKING UP HISTORY

The \f3gl_lookup_history()\f1 function allows the calling application
to look up lines in the history list.

.sp
.nf
  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);
.fi
.sp  

The \f3id\f1 argument indicates which line to look up, where the first
line that was entered in the history list after \f3new_GetLine()\f1
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
\f3gl_range_of_history()\f1 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 \f3hline\f1 argument, and
\f31\f1 is returned. Otherwise \f30\f1 is returned, and the variable
pointed to by \f3hline\f1 is left unchanged.
.sp
Beware that the string returned in \f3hline->line\f1 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 \f3gl\f1 as its
argument. Therefore you should make a private copy of this string if
you need to keep it around.

.SH MANUAL HISTORY ARCHIVAL

By default, whenever a line is entered by the user, it is
automatically appended to the history list, just before
\f3gl_get_line()\f1 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
\f3gl_automatic_history()\f1 function.

.sp
.nf
  int gl_automatic_history(GetLine *gl, int enable);
.fi
.sp

If this function is called with its \f3enable\f1 argument set to
\f30\f1, \f3gl_get_line()\f1 won't automatically archive subsequently
entered lines. Automatic archiving can be re-enabled at a later time,
by calling this function again, with its \f3enable\f1 argument set to
1.  While automatic history archiving is disabled, the calling
application can use the \f3gl_append_history()\f1 to append lines to
the history list as needed.

.sp
.nf
  int gl_append_history(GetLine *gl, const char *line);
.fi
.sp

The \f3line\f1 argument specifies the line to be added to the history
list. This must be a normal \f3'\0'\f1 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 \f3'\0'\f1 terminator.  If the line is
longer than the maximum input line length, that was specified when
\f3new_GetLine()\f1 was called, when the line is recalled, it will get
truncated to the actual \f3gl_get_line()\f1 line length.

If successful, \f3gl_append_history()\f1 returns 0. Otherwise it
returns non-zero, and sets \f3errno\f1 to one of the following values.

.sp
.nf
   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.
.fi
.sp

A textual description of the error can optionally be obtained by
calling \f3gl_error_message()\f1. 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
\f3gl_append_history()\f1.

.SH MISCELLANEOUS HISTORY CONFIGURATION

If you wish to change the size of the history buffer that was
originally specified in the call to \f3new_GetLine()\f1, you can do so
with the \f3gl_resize_history()\f1 function.

.sp
.nf
  int gl_resize_history(GetLine *gl, size_t histlen);
.fi
.sp

The \f3histlen\f1 argument specifies the new size in bytes, and if you
specify this as 0, the buffer will be deleted.
.sp
As mentioned in the discussion of \f3new_GetLine()\f1, 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 \f3gl_limit_history()\f1 function.

.sp
.nf
  void gl_limit_history(GetLine *gl, int max_lines);
.fi
.sp

The \f3max_lines\f1 should either be a positive number \f3>= 0\f1,
specifying an upper limit on the number of lines in the buffer, or be
\f3-1\f1 to cancel any previously specified limit. When a limit is in
effect, only the \f3max_lines\f1 most recently appended lines are kept
in the buffer. Older lines are discarded.
.sp
To discard lines from the history buffer, use the
\f3gl_clear_history()\f1 function.
.sp
.nf
  void gl_clear_history(GetLine *gl, int all_groups);
.fi
.sp
The \f3all_groups\f1 argument tells the function whether to delete
just the lines associated with the current history group (see
\f3gl_group_history()\f1), or all historical lines in the buffer.
.sp
The \f3gl_toggle_history()\f1 function allows you to toggle history on
and off without losing the current contents of the history list.

.sp
.nf
  void gl_toggle_history(GetLine *gl, int enable);
.fi
.sp

Setting the \f3enable\f1 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.

.SH QUERYING HISTORY INFORMATION

The configured state of the history list can be queried with the
\f3gl_history_state()\f1 function.

.sp
.nf
  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);
.fi
.sp
On return, the status information is recorded in the variable pointed
to by the \f3state\f1 argument.
.sp
The \f3gl_range_of_history()\f1 function returns the number and
range of lines in the history list.

.sp
.nf
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);
.fi
.sp
The return values are recorded in the variable pointed to by the
\f3range\f1 argument. If the \f3nlines\f1 member of this structure is
greater than zero, then the \f3oldest\f1 and \f3newest\f1 members
report the range of lines in the list, and \f3newest=oldest+nlines-1\f1.
Otherwise they are both zero.
.sp
The \f3gl_size_of_history()\f1 function returns the total size of the
history buffer and the amount of the buffer that is currently
occupied.
.sp
.nf
  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);
.fi
.sp
On return, the size information is recorded in the variable pointed to
by the \f3size\f1 argument.

.SH CHANGING TERMINALS

The \f3new_GetLine()\f1 constructor function assumes that input is to
be read from \f3stdin\f1, and output written to \f3stdout\f1. The
following function allows you to switch to different input and output
streams.
.sp
.nf
  int gl_change_terminal(GetLine *gl, FILE *input_fp,
                         FILE *output_fp, const char *term);
.fi
.sp
The \f3gl\f1 argument is the object that was returned by
\f3new_GetLine()\f1.  The \f3input_fp\f1 argument specifies the stream
to read from, and \f3output_fp\f1 specifies the stream to be written
to. Only if both of these refer to a terminal, will interactive
terminal input be enabled.  Otherwise \f3gl_get_line()\f1 will simply
call \f3fgets()\f1 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 \f3term\f1 argument. The value
of the \f3term\f1 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. \f3new_GetLine()\f1 for example, passes the return value of
\f3getenv("TERM")\f1 in this argument. Note that if one or both of
\f3input_fp\f1 and \f3output_fp\f1 don't refer to a terminal, then it
is legal to pass \f3NULL\f1 instead of a terminal type.
.sp
Note that if you want to pass file descriptors to
\f3gl_change_terminal()\f1, you can do this by creating stdio stream
wrappers using the POSIX \f3fdopen()\f1 function.

.SH EXTERNAL EVENT HANDLING

By default, \f3gl_get_line()\f1 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.

.sp
.nf
  1. Use the functions described in the
     \f3gl_io_mode(@FUNC_MANEXT@)\f1 man page to switch
     \f3gl_get_line()\f1 into non-blocking server mode. In this mode,
     \f3gl_get_line()\f1 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 \f3gl_get_line()\f1.

  2. While \f3gl_get_line()\f1 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 \f3select()\f1 system call,
     which is most, if not all flavors of unix.
.fi
.sp

Registering a file descriptor to be watched by
\f3gl_get_line()\f1 involves calling the \f3gl_watch_fd()\f1 function.

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

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.
.sp
The \f3fd\f1 argument is the file descriptor to be watched. The
\f3event\f1 argument specifies what type of activity is of interest,
chosen from the following enumerated values:

.sp
.nf
  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.
.fi
.sp

The \f3callback\f1 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.

.sp
.nf
  #define GL_FD_EVENT_FN(fn) GlFdStatus (fn)(GetLine *gl, \\
                                      void *data, int fd, \\
                                      GlFdEvent event)
.fi
.sp
The \f3data\f1 argument of the \f3gl_watch_fd()\f1 function is passed
to the callback function for its own use, and can point to anything
you like, including \f3NULL\f1. 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.

.sp
.nf
  GLFD_ABORT    -  Tell gl_get_line() to abort. When this
                   happens, \f3gl_get_line()\f1 returns
                   \f3NULL\f1, and a following call to
                   \f3gl_return_status()\f1 will return
                   \f3GLR_FDABORT\f1. Note that if the
                   application needs \f3errno\f1 always to
                   have a meaningful value when
                   \f3gl_get_line()\f1 returns \f3NULL\f1,
                   the callback function should set
                   \f3errno\f1 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.
.fi
.sp
Note that before calling the callback, \f3gl_get_line()\f1 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.

.sp

If the callback function needs to read or write to the terminal, it
should ideally first call \f3gl_normal_io(gl)\f1 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, \f3gl_get_line()\f1 will
notice that \f3gl_normal_io()\f1 was called, redisplay the input line
and resume editing. Note that in this case the return values,
\f3GLFD_REFRESH\f1 and \f3GLFD_CONTINUE\f1 are equivalent.

.sp

To support cases where the callback function calls a third-party
function which occasionally and unpredictably writes to the terminal,
the automatic conversion of \f3"\n"\f1 to \f3"\r\n"\f1 is re-enabled
before the callback function is called. If the callack knows that the
third-party function wrote to the terminal, it should then return the
\f3GLFD_REFRESH\f1 return value, to tell \f3gl_get_line()\f1 to
redisplay the input line.

.sp

To remove a callback function that you previously registered for a
given file descriptor and event, simply call \f3gl_watch_fd()\f1 with
the same file descriptor and \f3event\f1 arguments, but with a
\f3callback\f1 argument of \f30\f1. The \f3data\f1 argument is ignored
in this case.

.SH SETTING AN INACTIVITY TIMEOUT

On systems with the \f3select()\f1 system call, the
\f3gl_inactivity_timeout()\f1 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 \f3gl_watch_fd()\f1. On oddball systems that don't
have \f3select()\f1, this call has no effect.

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

The timeout is specified in the form of an integral number of seconds
and an integral number of nanoseconds, via the \f3sec\f1 and
\f3nsec\f1 arguments respectively. Subsequently, whenever no activity
is seen for this time period, the function specified via the
\f3callback\f1 argument is called. The \f3data\f1 argument of
\f3gl_inactivity_timeout()\f1 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 \f3libtecla.h\f1 for applications to use to declare and
prototype timeout callback functions.

.sp
.nf
  #define GL_TIMEOUT_FN(fn) \\
               GlAfterTimeout (fn)(GetLine *gl, void *data)
.fi
.sp

On returning, the application's callback is expected to return one of
the following enumerators to tell \f3gl_get_line()\f1 how to procede
after the timeout has been handled by the callback.

.sp
.nf
  GLTO_ABORT    -  Tell gl_get_line() to abort. When
                   this happens, \f3gl_get_line()\f1 will
                   return \f3NULL\f1, and a following call
                   to \f3gl_return_status()\f1 will return
                   \f3GLR_TIMEOUT\f1. Note that if the
                   application needs \f3errno\f1 always to
                   have a meaningful value when
                   \f3gl_get_line()\f1 returns \f3NULL\f1,
                   the callback function should set
                   \f3errno\f1 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
                   \f3gl_normal_io(gl)\f1.
  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(@FUNC_MANEXT@)), cause \f3gl_get_line()\f1
                   to act as though I/O blocked. This means
                   that \f3gl_get_line()\f1 will immediately
                   return \f3NULL\f1, and a following call
                   to \f3gl_return_status()\f1 will return
                   \f3GLR_BLOCKED\f1.
.fi
.sp

Note that before calling the callback, \f3gl_get_line()\f1 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.

.sp

If the callback function needs to read or write to the terminal, it
should ideally first call \f3gl_normal_io(gl)\f1 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, \f3gl_get_line()\f1 will
notice that \f3gl_normal_io()\f1 was called, redisplay the input line
and resume editing. Note that in this case the return values,
\f3GLTO_REFRESH\f1 and \f3GLTO_CONTINUE\f1 are equivalent.

.sp

To support cases where the callback function calls a third-party
function which occasionally and unpredictably writes to the terminal,
the automatic conversion of \f3"\n"\f1 to \f3"\r\n"\f1 is re-enabled
before the callback function is called. If the callack knows that the
third-party function wrote to the terminal, it should then return the
\f3GLTO_REFRESH\f1 return value, to tell \f3gl_get_line()\f1 to
redisplay the input line.

.sp

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
\f3sysconf(_SC_CLK_TCK)\f1).

.sp

To turn off timeouts, simply call \f3gl_inactivity_timeout()\f1 with a
\f3callback\f1 argument of \f30\f1. The \f3data\f1 argument is ignored
in this case.

.SH SIGNAL HANDLING DEFAULTS

By default, the \f3gl_get_line()\f1 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 \f3gl_get_line()\f1 responds to them, is
described. Changing these defaults is the topic of the
following section.
.sp
When the following subset of signals are caught, \f3gl_get_line()\f1
first restores the terminal settings and signal handling to how they
were before \f3gl_get_line()\f1 was called, resends the signal, to
allow the calling application's signal handlers to handle it, then if
the process still exists, \f3gl_get_line()\f1 returns \f3NULL\f1 and
sets \f3errno\f1 as specified below.

.sp
.nf
 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 \f3gl_change_terminal()\f1 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
.fi
.sp
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 \f3SIGQUIT\f1 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 \f3gl_get_line()\f1 returns.
.sp
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.
.sp
.nf
  int gl_last_signal(const GetLine *gl);
.fi
.sp
This returns the numeric code (eg. \f3SIGINT\f1) of the last signal
that was received during the most recent call to \f3gl_get_line()\f1,
or \f3-1\f1 if no signals were received.
.sp
On systems that support it, when a SIGWINCH (window change) signal is
received, \f3gl_get_line()\f1 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.
.sp
Finally, the following signals cause \f3gl_get_line()\f1 to first
restore the terminal and signal environment to that which prevailed
before \f3gl_get_line()\f1 was called, then resend the signal to the
application. If the process still exists after the signal has been
delivered, then \f3gl_get_line()\f1 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.
.sp
.nf
 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 \f3gl_get_line()\f1 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.
.fi
.sp

Obviously not all of the above signals are supported on all systems,
so code to support them is conditionally compiled into the tecla
library.
.sp
Note that if \f3SIGKILL\f1 or \f3SIGPOLL\f1, which by definition can't
be caught, or any of the hardware generated exception signals, such as
\f3SIGSEGV\f1, \f3SIGBUS\f1 and \f3SIGFPE\f1, are received and
unhandled while \f3gl_get_line()\f1 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.

.SH CUSTOMIZED SIGNAL HANDLING

The previous section listed the signals that
\f3gl_get_line()\f1 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 \f3gl_get_line()\f1 should respond to a given
signal.
.sp
If you don't need \f3gl_get_line()\f1 to do anything in
response to a signal that it normally traps, you can tell to
\f3gl_get_line()\f1 to ignore that signal by calling
\f3gl_ignore_signal()\f1.
.sp
.nf
  int gl_ignore_signal(GetLine *gl, int signo);
.fi
.sp
The \f3signo\f1 argument is the number of the signal
(eg. \f3SIGINT\f1) that you want to have ignored. If the
specified signal isn't currently one of those being trapped,
this function does nothing.
.sp
The \f3gl_trap_signal()\f1 function allows you to either add
a new signal to the list that \f3gl_get_line()\f1 traps, or
modify how it responds to a signal that it already traps.
.sp
.nf
  int gl_trap_signal(GetLine *gl, int signo, unsigned flags,
                     GlAfterSignal after, int errno_value);
.fi
.sp
The \f3signo\f1 argument is the number of the signal that
you wish to have trapped. The \f3flags\f1 argument is a set
of flags which determine the environment in which the
application's signal handler is invoked, the \f3after\f1
argument tells \f3gl_get_line()\f1 what to do after the
application's signal handler returns, and \f3errno_value\f1
tells \f3gl_get_line()\f1 what to set \f3errno\f1 to if told
to abort.
.sp
The \f3flags\f1 argument is a bitwise OR of zero or more of
the following enumerators:
.sp
.nf
  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.
.fi
.sp
Two commonly useful flag combinations are also enumerated as
follows:
.sp
.nf
  GLS_RESTORE_ENV   = GLS_RESTORE_SIG | GLS_RESTORE_TTY |
                      GLS_REDRAW_LINE

  GLS_SUSPEND_INPUT = GLS_RESTORE_ENV | GLS_RESTORE_LINE
.fi
.sp

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 \f3flags\f1
argument to \f30\f1.
.sp
If your signal handler always writes to the terminal, reads
from it, or suspends or terminates the program, you should
specify the \f3flags\f1 argument as \f3GL_SUSPEND_INPUT\f1,
so that:
.sp
.nf
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
   \f3\\r\\n\f1, instead of just \f3\\n\f1.
.fi
.sp
The \f3GL_RESTORE_ENV\f1 combination is the same as
\f3GL_SUSPEND_INPUT\f1, 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 \f3GL_SUSPEND_LINE\f1 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
\f3\\n\f1 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
\f3GL_SUSPEND_INPUT\f1. 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 \f3GL_SUSPEND_INPUT\f1 combination is better if you
know that you are always going to be writing to the
terminal.
.sp
The \f3after\f1 argument, which determines what
\f3gl_get_line()\f1 does after the application's signal
handler returns (if it returns), can take any one of the
following values:
.sp
.nf
  GLS_RETURN   - Return the completed input line, just as
                 though the user had pressed the return
                 key.

  GLS_ABORT    - Cause \f3gl_get_line()\f1 to abort. When
                 this happens, \f3gl_get_line()\f1 returns
                 \f3NULL\f1, and a following call to
                 \f3gl_return_status()\f1 will return
                 \f3GLR_SIGNAL\f1. Note that if the
                 application needs \f3errno\f1 always to
                 have a meaningful value when
                 \f3gl_get_line()\f1 returns \f3NULL\f1,
                 the callback function should set
                 \f3errno\f1 appropriately.
  GLS_CONTINUE - Resume command line editing. 
.fi
.sp
The \f3errno_value\f1 argument is intended to be combined
with the \f3GLS_ABORT\f1 option, telling \f3gl_get_line()\f1
what to set the standard \f3errno\f1 variable to before
returning \f3NULL\f1 to the calling program. It can also,
however, be used with the \f3GL_RETURN\f1 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.

.SH RELIABLE SIGNAL HANDLING

Signal handling is suprisingly hard to do reliably without race
conditions. In \f3gl_get_line()\f1 a lot of care has been taken to
allow applications to perform reliable signal handling around
\f3gl_get_line()\f1. 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 \f3gl_get_line()\f1. 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 \f3gl_get_line()\f1, then \f3gl_get_line()\f1 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 \f3gl_get_line()\f1
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 \f3gl_trap_signal()\f1 function to
   configure \f3gl_get_line()\f1 to abort when important
   signals are caught.

2. Configure \f3gl_get_line()\f1 such that if any of the
   signals that it catches are blocked when
   \f3gl_get_line()\f1 is called, they will be unblocked
   automatically during times when \f3gl_get_line()\f1 is
   waiting for I/O. This can be done either
   on a per signal basis, by calling the
   \f3gl_trap_signal()\f1 function, and specifying the
   \f3GLS_UNBLOCK\f1 attribute of the signal, or globally by
   calling the \f3gl_catch_blocked()\f1 function.

.sp
.nf
     void gl_catch_blocked(GetLine *gl);
.fi
.sp

   This function simply adds the \f3GLS_UNBLOCK\f1 attribute
   to all of the signals that it is currently configured to
   trap.

3. Just before calling \f3gl_get_line()\f1, block delivery
   of all of the signals that \f3gl_get_line()\f1 is
   configured to trap. This can be done using the POSIX
   \f3sigprocmask()\f1 function in conjunction with the
   \f3gl_list_signals()\f1 function.

.sp
.nf
      int gl_list_signals(GetLine *gl, sigset_t *set);
.fi
.sp

   This function returns the set of signals that it is
   currently configured to catch in the \f3set\f1 argument,
   which is in the form required by \f3sigprocmask()\f1.

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
   \f3gl_get_line()\f1 unblocks its signals while performing
   I/O.

5. Eventually \f3gl_get_line()\f1 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 \f3sigprocmask()\f1 to unblock the signals that were
   blocked in step 3.

The same technique can be used around certain POSIX
signal-aware functions, such as \f3sigsetjmp()\f1 and
\f3sigsuspend()\f1, and in particular, the former of these
two functions can be used in conjunction with
\f3siglongjmp()\f1 to implement race-condition free signal
handling around other long-running system calls. The way to
do this, is explained next, by showing how
\f3gl_get_line()\f1 manages to reliably trap signals around
calls to functions like \f3read()\f1 and \f3select()\f1
without race conditions.

The first thing that \f3gl_get_line()\f1 does, whenever it
is called, is to use the POSIX \f3sigprocmask()\f1 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 \f3gl_get_line()\f1 needs to call \f3read()\f1 or
\f3select()\f1 to wait for input from the user, it first
calls the POSIX \f3sigsetjmp()\f1 function, being sure to
specify a non-zero value for its \f3savesigs\f1 argument.
The reason for the latter argument will become clear
shortly.

If \f3sigsetjmp()\f1 returns zero, \f3gl_get_line()\f1 then
does the following.

.sp
.nf
a. It uses the POSIX \f3sigaction()\f1 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 \f3siglongjmp()\f1
      function using the buffer that was passed to
      \f3sigsetjmp()\f1 for its first argument, and
      a non-zero value for its second argument.

   When this signal handler is registered, the \f3sa_mask\f1
   member of the \f3struct sigaction act\f1 argument of the
   call to \f3sigaction()\f1 is configured to contain all of
   the signals that \f3gl_get_line()\f1 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,
   \f3gl_get_line()\f1 unblocks all of the signals that it
   is configured to catch.

c. It then calls the \f3read()\f1 or \f3select()\f1 system
   calls to wait for keyboard input.

d. If this system call returns (ie. no signal is received),
   \f3gl_get_line()\f1 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.
.fi
.sp

Alternatively, if \f3sigsetjmp()\f1 returns non-zero, this
means that one of the signals being trapped was caught while
the above steps were executing. When this happens,
\f3gl_get_line()\f1 does the following.

First, note that when a call to \f3siglongjmp()\f1 causes
\f3sigsetjmp()\f1 to return, provided that the
\f3savesigs\f1 argument of \f3sigsetjmp()\f1 was non-zero,
as specified above, the signal process mask is restored to
how it was when \f3sigsetjmp()\f1 was called. This is the
important difference between \f3sigsetjmp()\f1 and the older
problematic \f3setjmp()\f1, 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 \f3sigsetjmp()\f1
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 \f3gl_get_line()\f1 configuration
   attributes of the signal that was caught,
   \f3gl_get_line()\f1 restores the terminal attributes to
   the state that they had when \f3gl_get_line()\f1 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 \f3raise()\f1
   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 \f3raise()\f1, 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), \f3gl_get_line()\f1 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. \f3gl_get_line()\f1 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 \f3gl_get_line()\f1 has
complete control over its environment.

.SH THE TERMINAL SIZE

On most systems the combination of the \f3TIOCGWINSZ\f1 ioctl and the
\f3SIGWINCH\f1 signal is used to maintain an accurate idea of the
terminal size. The terminal size is newly queried every time that
\f3gl_get_line()\f1 is called and whenever a \f3SIGWINCH\f1 signal is
received.
.sp
On the few systems where this mechanism isn't available, at
startup \f3new_GetLine()\f1 first looks for the \f3LINES\f1
and \f3COLUMNS\f1 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.
.sp
Even on systems that do support \f3ioctl(TIOCGWINSZ)\f1, 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 \f3SIGWINCH\f1 is sent to
the process, and the dimensions returned by \f3ioctl(TIOCGWINSZ)\f1
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
\f3gl_set_term_size()\f1 function to tell \f3gl_get_line()\f1 about
the change in size.

.sp
.nf
  int gl_set_term_size(GetLine *gl, int ncolumn, int nline);
.fi
.sp

The \f3ncolumn\f1 and \f3nline\f1 arguments are used to specify the
new dimensions of the terminal, and must not be less than 1. On
systems that do support \f3ioctl(TIOCGWINSZ)\f1, this function first
calls \f3ioctl(TIOCSWINSZ)\f1 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 \f3gl\f1 for
future use by \f3gl_get_line()\f1.
.sp
The \f3gl_terminal_size()\f1 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.
.sp
.nf
  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);
.fi
.sp
This function first updates \f3gl_get_line()\f1's fallback terminal
dimensions, then records its findings in the return value.
.sp
The \f3def_ncolumn\f1 and \f3def_nline\f1 specify the
default number of terminal columns and lines to use if the
terminal size can't be determined via \f3ioctl(TIOCGWINSZ)\f1 or
environment variables.

.SH 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 \f3gl_echo_mode()\f1
function allows you to toggle on and off the display and archival of
any text that is subsequently entered in calls to \f3gl_get_line()\f1.

.sp
.nf
  int gl_echo_mode(GetLine *gl, int enable);
.fi
.sp

The \f3enable\f1 argument specifies whether entered text
should be visible or not. If it is \f30\f1, then
subsequently entered lines will not be visible on the
terminal, and will not be recorded in the history list. If
it is \f31\f1, then subsequent input lines will be displayed
as they are entered, and provided that history hasn't been
turned off via a call to \f3gl_toggle_history()\f1, then
they will also be archived in the history list. Finally, if
the \f3enable\f1 argument is \f3-1\f1, 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 \f30\f1 if
echoing was disabled before the function was called, and
\f31\f1 if it was enabled.
.sp
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.

.SH SINGLE CHARACTER QUERIES

Using \f3gl_get_line()\f1 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 \f3gl_query_char()\f1 function has been provided for
single character queries like this.

.sp
.nf
  int gl_query_char(GetLine *gl, const char *prompt,
                    char defchar);
.fi
.sp

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, \f3gl_query_char()\f1 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, \f3EOF\f1 is
returned instead. In the latter case, the application can call the
previously documented \f3gl_return_status()\f1, 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 \f3defchar\f1 argument
is substituted. This means that when the user hits either newline or
return, the character specified in \f3defchar\f1, 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 \f3'\n'\f1 as the value of \f3defchar\f1.

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 \f3gl_get_line()\f1, echoing of the entered character can be
disabled using the \f3gl_echo_mode()\f1 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
\f3gl_query_char()\f1 resumes waiting for the user to type a
character.

Note that in non-blocking server mode, (see
gl_io_mode(@FUNC_MANEXT@)), if an incomplete input line is in the
process of being read when \f3gl_query_char()\f1 is called, the
partial input line is discarded, and erased from the terminal, before
the new prompt is displayed. The next call to \f3gl_get_line()\f1 will
thus start editing a new line.

.SH READING RAW CHARACTERS

Whereas the \f3gl_query_char()\f1 function visibly prompts the user
for a character, and displays what they typed, the
\f3gl_read_char()\f1 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 \f3gl_get_line()\f1, but also from callback
functions that the application has registered to be called by
\f3gl_get_line()\f1.

.sp
.nf
  int gl_read_char(GetLine *gl);
.fi
.sp

On success, the return value of \f3gl_read_char()\f1 is the character
that was read. On failure, \f3EOF\f1 is returned, and the
\f3gl_return_status()\f1 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
\f3gl_read_char()\f1 won't be enough to identify such keystrokes.

.SH CLEARING THE TERMINAL

The calling program can clear the terminal by calling
\f3gl_erase_terminal()\f1. In non-blocking server-I/O mode, this
function also arranges for the current input line to be redrawn from
scratch when \f3gl_get_line()\f1 is next called.

.sp
.nf
  int gl_erase_terminal(GetLine *gl);
.fi
.sp

.SH DISPLAYING TEXT DYNAMICALLY

Between calls to \f3gl_get_line()\f1, the \f3gl_display_text()\f1
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.

.sp
.nf
  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);
.fi
.sp
If \f3gl\f1 isn't currently connected to a terminal, for example if
the output of a program that uses \f3gl_get_line()\f1 is being piped
to another program or redirected to a file, then the value of the
\f3def_width\f1 parameter is used as the terminal width.

The \f3indentation\f1 argument specifies the number of characters to
use to indent each line of output. The \f3fill_char\f1 argument
specifies the character that will be used to perform this indentation.

The \f3prefix\f1 argument can either be \f3NULL\f1, or be a string to
place at the beginning of each new line (after any indentation).
Similarly, the \f3suffix\f1 argument can either be \f3NULL\f1, 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 \f3fill_char\f1 argument.  Normally the
fill-character is a space.

The \f3start\f1 argument tells \f3gl_display_text()\f1 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 \f3gl_display_text()\f1 is the ending column index of
the cursor, by passing the return value of one call to the \f3start\f1
argument of the next call, a paragraph that is broken between more
than one string can be composed by calling \f3gl_display_text()\f1 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, \f3gl_display_text()\f1 returns -1.

.SH 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.
.sp
Calling the \f3gl_replace_prompt()\f1 function from a
callback tells \f3gl_get_line()\f1 to display a different
prompt when the callback returns. Except in non-blocking
server mode, it has no effect if used between calls to
\f3gl_get_line()\f1. In non-blocking server mode (see the
\f3gl_io_mode(@FUNC_MANEXT@)\f1 man page, when used between two calls to
\f3gl_get_line()\f1 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 \f3gl_get_line()\f1.

.sp
.nf
  void gl_replace_prompt(GetLine *gl, const char *prompt);
.fi
.sp

.SH INTERNATIONAL CHARACTER SETS

Since libtecla version 1.4.0, \f3gl_get_line()\f1 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,
.sp
.nf
  setlocale(LC_CTYPE, "");
.fi
.sp
then the current locale is determined by the first of the environment
variables \f3LC_CTYPE\f1, \f3LC_ALL\f1, and \f3LANG\f1, 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
\f3C\f1 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:
.sp
.nf
  locale -a
.fi
.sp
at the shell prompt. Further documentation on how the user can make use
of this to enter international characters can be found in the
\f3tecla(@MISC_MANEXT@)\f1 man page.

.SH 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.

.SH FILES
.nf
libtecla.a      -    The tecla library
libtecla.h      -    The tecla header file.
~/.teclarc      -    The personal tecla customization file.
.fi

.SH SEE ALSO
.nf
libtecla(@LIBR_MANEXT@), gl_io_mode(@FUNC_MANEXT@), tecla(@MISC_MANEXT@), ef_expand_file(@FUNC_MANEXT@),
cpl_complete_word(@FUNC_MANEXT@), pca_lookup_file(@FUNC_MANEXT@)
.fi

.SH AUTHOR
Martin Shepherd  (mcs@astro.caltech.edu)