Provided by: libtecla-dev_1.6.3-1_amd64 
NAME
gl_get_line, new_GetLine, del_GetLine, gl_customize_completion, gl_change_terminal,
gl_configure_getline, gl_load_history, gl_save_history, gl_group_history, gl_show_history,
gl_watch_fd, gl_inactivity_timeout, gl_terminal_size, gl_set_term_size, gl_resize_history,
gl_limit_history, gl_clear_history, gl_toggle_history, gl_lookup_history,
gl_state_of_history, gl_range_of_history, gl_size_of_history, gl_echo_mode,
gl_replace_prompt, gl_prompt_style, gl_ignore_signal, gl_trap_signal, gl_last_signal,
gl_completion_action, gl_display_text, gl_return_status, gl_error_message,
gl_catch_blocked, gl_list_signals, gl_bind_keyseq, gl_erase_terminal,
gl_automatic_history, gl_append_history, gl_query_char, gl_read_char - allow the user to
compose an input line
SYNOPSIS
#include <stdio.h>
#include <libtecla.h>
GetLine *new_GetLine(size_t linelen, size_t histlen);
GetLine *del_GetLine(GetLine *gl);
char *gl_get_line(GetLine *gl, const char *prompt,
const char *start_line, int start_pos);
int gl_query_char(GetLine *gl, const char *prompt,
char defchar);
int gl_read_char(GetLine *gl);
int gl_customize_completion(GetLine *gl, void *data,
CplMatchFn *match_fn);
int gl_change_terminal(GetLine *gl, FILE *input_fp,
FILE *output_fp, const char *term);
int gl_configure_getline(GetLine *gl,
const char *app_string,
const char *app_file,
const char *user_file);
int gl_bind_keyseq(GetLine *gl, GlKeyOrigin origin,
const char *keyseq, const char *action);
int gl_save_history(GetLine *gl, const char *filename,
const char *comment, int max_lines);
int gl_load_history(GetLine *gl, const char *filename,
const char *comment);
int gl_watch_fd(GetLine *gl, int fd, GlFdEvent event,
GlFdEventFn *callback, void *data);
int gl_inactivity_timeout(GetLine *gl, GlTimeoutFn *callback,
void *data, unsigned long sec,
unsigned long nsec);
int gl_group_history(GetLine *gl, unsigned stream);
int gl_show_history(GetLine *gl, FILE *fp,
const char *fmt, int all_groups,
int max_lines);
int gl_resize_history(GetLine *gl, size_t bufsize);
void gl_limit_history(GetLine *gl, int max_lines);
void gl_clear_history(GetLine *gl, int all_groups);
void gl_toggle_history(GetLine *gl, int enable);
GlTerminalSize gl_terminal_size(GetLine *gl,
int def_ncolumn,
int def_nline);
int gl_set_term_size(GetLine *gl, int ncolumn, int nline);
int gl_lookup_history(GetLine *gl, unsigned long id,
GlHistoryLine *hline);
void gl_state_of_history(GetLine *gl,
GlHistoryState *state);
void gl_range_of_history(GetLine *gl,
GlHistoryRange *range);
void gl_size_of_history(GetLine *gl, GlHistorySize *size);
void gl_echo_mode(GetLine *gl, int enable);
void gl_replace_prompt(GetLine *gl, const char *prompt);
void gl_prompt_style(GetLine *gl, GlPromptStyle style);
int gl_ignore_signal(GetLine *gl, int signo);
int gl_trap_signal(GetLine *gl, int signo, unsigned flags,
GlAfterSignal after, int errno_value);
int gl_last_signal(GetLine *gl);
int gl_completion_action(GetLine *gl,
void *data, CplMatchFn *match_fn,
int list_only, const char *name,
const char *keyseq);
int gl_register_action(GetLine *gl, void *data,
GlActionFn *fn, const char *name,
const char *keyseq);
int gl_display_text(GetLine *gl, int indentation,
const char *prefix,
const char *suffix, int fill_char,
int def_width, int start,
const char *string);
GlReturnStatus gl_return_status(GetLine *gl);
const char *gl_error_message(GetLine *gl, char *buff,
size_t n);
void gl_catch_blocked(GetLine *gl);
int gl_list_signals(GetLine *gl, sigset_t *set);
int gl_append_history(GetLine *gl, const char *line);
int gl_automatic_history(GetLine *gl, int enable);
DESCRIPTION
The gl_get_line() function is part of the tecla library (see the libtecla(3) man page). If
the user is typing at a terminal, each call prompts them for an line of input, then
provides interactive editing facilities, similar to those of the unix tcsh shell. In
addition to simple command-line editing, it supports recall of previously entered command
lines, TAB completion of file names, and in-line wild-card expansion of filenames.
Documentation of both the user-level command-line editing features and all user
configuration options, can be found in the tecla(7) man page. This man page concerns
itself with documentation for programmers interested in using this library in their
application.
AN EXAMPLE
The following shows a complete example of how to use the gl_get_line() function to get
input from the user:
#include <stdio.h>
#include <locale.h>
#include <libtecla.h>
int main(int argc, char *argv[])
{
char *line; /* The line that the user typed */
GetLine *gl; /* The gl_get_line() resource object */
setlocale(LC_CTYPE, ""); /* Adopt the user's choice */
/* of character set. */
gl = new_GetLine(1024, 2048);
if(!gl)
return 1;
while((line=gl_get_line(gl, "$ ", NULL, -1)) != NULL &&
strcmp(line, "exit\n") != 0)
printf("You typed: %s\n", line);
gl = del_GetLine(gl);
return 0;
}
In the example, first the resources needed by the gl_get_line() function are created by
calling new_GetLine(). This allocates the memory used in subsequent calls to the
gl_get_line() function, including the history buffer for recording previously entered
lines. Then one or more lines are read from the user, until either an error occurs, or the
user types exit. Then finally the resources that were allocated by new_GetLine(), are
returned to the system by calling del_GetLine(). Note the use of the NULL return value of
del_GetLine() to make gl NULL. This is a safety precaution. If the program subsequently
attempts to pass gl to gl_get_line(), said function will complain, and return an error,
instead of attempting to use the deleted resource object.
THE FUNCTIONS USED IN THE EXAMPLE
The descriptions of the functions used in the example are as follows:
GetLine *new_GetLine(size_t linelen, size_t histlen)
This function creates the resources used by the gl_get_line() function and returns an
opaque pointer to the object that contains them. The maximum length of an input line is
specified via the linelen argument, and the number of bytes to allocate for storing
history lines is set by the histlen argument. History lines are stored back-to-back in a
single buffer of this size. Note that this means that the number of history lines that can
be stored at any given time, depends on the lengths of the individual lines. If you want
to place an upper limit on the number of lines that can be stored, see the
gl_limit_history() function described later. If you don't want history at all, specify
histlen as zero, and no history buffer will be allocated.
On error, a message is printed to stderr and NULL is returned.
GetLine *del_GetLine(GetLine *gl)
This function deletes the resources that were returned by a previous call to
new_GetLine(). It always returns NULL (ie a deleted object). It does nothing if the gl
argument is NULL.
char *gl_get_line(GetLine *gl, const char *prompt,
const char *start_line, int start_pos);
The gl_get_line() function can be called any number of times to read input from the user.
The gl argument must have been previously returned by a call to new_GetLine(). The prompt
argument should be a normal NUL terminated string, specifying the prompt to present the
user with. By default prompts are displayed literally, but if enabled with the
gl_prompt_style() function (see later), prompts can contain directives to do underlining,
switch to and from bold fonts, or turn highlighting on and off.
If you want to specify the initial contents of the line, for the user to edit, pass the
desired string via the start_line argument. You can then specify which character of this
line the cursor is initially positioned over, using the start_pos argument. This should be
-1 if you want the cursor to follow the last character of the start line. If you don't
want to preload the line in this manner, send start_line as NULL, and set start_pos to -1.
Note that the line pointer returned by one call to gl_get_line() can be passed back to the
next call to gl_get_line() via the start_line. This allows the application to take the
last entered line, and if it contains an error, to then present it back to the user for
re-editing, with the cursor initially positioned where the error was encountered.
The gl_get_line() function returns a pointer to the line entered by the user, or NULL on
error or at the end of the input. The returned pointer is part of the specified gl
resource object, and thus should not be free'd by the caller, or assumed to be unchanging
from one call to the next. When reading from a user at a terminal, there will always be a
newline character at the end of the returned line. When standard input is being taken
from a pipe or a file, there will similarly be a newline unless the input line was too
long to store in the internal buffer. In the latter case you should call gl_get_line()
again to read the rest of the line. Note that this behavior makes gl_get_line() similar to
fgets(). In fact when stdin isn't connected to a terminal,gl_get_line() just calls
fgets().
THE RETURN STATUS OF GL_GET_LINE
As described above, the gl_get_line() function has two possible return values; a pointer
to the completed input line, or NULL. Extra information about what caused gl_get_line() to
return is available both by inspecting errno, and by calling the gl_return_status()
function.
GlReturnStatus gl_return_status(GetLine *gl);
The following are the possible enumerated values that this function returns.
GLR_NEWLINE - The last call to gl_get_line()
successfully returned a completed
input line.
GLR_BLOCKED - gl_get_line() was in non-blocking
server mode, and returned early to
avoid blocking the process while
waiting for terminal I/O. The
gl_pending_io() function can be
used to see what type of I/O
gl_get_line() was waiting for.
(see the gl_io_mode(3) man page
for details).
GLR_SIGNAL - A signal was caught by
gl_get_line() that had an
after-signal disposition of
GLS_ABORT (See gl_trap_signal()).
GLR_TIMEOUT - The inactivity timer expired while
gl_get_line() was waiting for
input, and the timeout callback
function returned GLTO_ABORT.
See gl_inactivity_timeout() for
information about timeouts.
GLR_FDABORT - An application I/O callack returned
GLFD_ABORT (see gl_watch_fd()).
GLR_EOF - End of file reached. This can happen
when input is coming from a file or a
pipe, instead of the terminal. It also
occurs if the user invokes the
list-or-eof or del-char-or-list-or-eof
actions at the start of a new line.
GLR_ERROR - An unexpected error caused
gl_get_line() to abort (consult
errno and/or
gl_error_message() for details.
When gl_return_status() returns GLR_ERROR, and the value of errno isn't sufficient to
explain what happened, you can use the gl_error_message() function to request a
description of the last error that occurred.
const char *gl_error_message(GetLine *gl, char *buff,
size_t n);
The return value is a pointer to the message that occurred. If the buff argument is NULL,
this will be a pointer to a buffer within gl, who's value will probably change on the next
call to any function associated with gl_get_line(). Otherwise, if a non-NULL buff argument
is provided, the error message, including a '\0' terminator, will be written within the
first n elements of this buffer, and the return value will be a pointer to the first
element of this buffer. If the message won't fit in the provided buffer, it will be
truncated to fit.
OPTIONAL PROMPT FORMATTING
Whereas by default the prompt string that you specify is displayed literally, without any
special interpretation of the characters within it, the gl_prompt_style() function can be
used to enable optional formatting directives within the prompt.
void gl_prompt_style(GetLine *gl, GlPromptStyle style);
The style argument, which specifies the formatting style, can take any of the following
values:
GL_FORMAT_PROMPT - In this style, the formatting
directives described below, when
included in prompt strings, are
interpreted as follows:
%B - Display subsequent
characters with a bold
font.
%b - Stop displaying characters
with the bold font.
%F - Make subsequent characters
flash.
%f - Turn off flashing
characters.
%U - Underline subsequent
characters.
%u - Stop underlining
characters.
%P - Switch to a pale (half
brightness) font.
%p - Stop using the pale font.
%S - Highlight subsequent
characters (also known as
standout mode).
%s - Stop highlighting
characters.
%V - Turn on reverse video.
%v - Turn off reverse video.
%% - Display a single %
character.
For example, in this mode, a prompt
string like "%UOK%u$ " would
display the prompt "OK$ ",
but with the OK part
underlined.
Note that although a pair of
characters that starts with a %
character, but doesn't match any of
the above directives is displayed
literally, if a new directive is
subsequently introduced which does
match, the displayed prompt will
change, so it is better to always
use %% to display a literal %.
Also note that not all terminals
support all of these text
attributes, and that some substitute
a different attribute for missing
ones.
GL_LITERAL_PROMPT - In this style, the prompt string is
printed literally. This is the
default style.
ALTERNATE CONFIGURATION SOURCES
As mentioned above, by default users have the option of configuring the behavior of
gl_get_line() via a configuration file called .teclarc in their home directories. The fact
that all applications share this same configuration file is both an advantage and a
disadvantage. In most cases it is an advantage, since it encourages uniformity, and frees
the user from having to configure each application separately. In some applications,
however, this single means of configuration is a problem. This is particularly true of
embedded software, where there's no filesystem to read a configuration file from, and also
in applications where a radically different choice of keybindings is needed to emulate a
legacy keyboard interface. To cater for such cases, the following function allows the
application to control where configuration information is read from.
int gl_configure_getline(GetLine *gl,
const char *app_string,
const char *app_file,
const char *user_file);
It allows the configuration commands that would normally be read from a user's ~/.teclarc
file, to be read from any or none of, a string, an application specific configuration
file, and/or a user-specific configuration file. If this function is called before the
first call to gl_get_line(), the default behavior of reading ~/.teclarc on the first call
to gl_get_line() is disabled, so all configuration must be achieved using the
configuration sources specified with this function.
If app_string != NULL, then it is interpreted as a string containing one or more
configuration commands, separated from each other in the string by embedded newline
characters. If app_file != NULL then it is interpreted as the full pathname of an
application-specific configuration file. If user_file != NULL then it is interpreted as
the full pathname of a user-specific configuration file, such as ~/.teclarc. For example,
in the following call,
gl_configure_getline(gl, "edit-mode vi \n nobeep",
"/usr/share/myapp/teclarc",
"~/.teclarc");
the app_string argument causes the calling application to start in vi edit-mode, instead
of the default emacs mode, and turns off the use of the terminal bell by the library. It
then attempts to read system-wide configuration commands from an optional file called
/usr/share/myapp/teclarc, then finally reads user-specific configuration commands from an
optional .teclarc file in the user's home directory. Note that the arguments are listed in
ascending order of priority, with the contents of app_string being potentially overridden
by commands in app_file, and commands in app_file potentially being overridden by commands
in user_file.
You can call this function as many times as needed, the results being cumulative, but note
that copies of any filenames specified via the app_file and user_file arguments are
recorded internally for subsequent use by the read-init-files key-binding function, so if
you plan to call this function multiple times, be sure that the last call specifies the
filenames that you want re-read when the user requests that the configuration files be re-
read.
Individual key sequences can also be bound and unbound using the gl_bind_keyseq()
function.
int gl_bind_keyseq(GetLine *gl, GlKeyOrigin origin,
const char *keyseq,
const char *action);
The origin argument specifies the priority of the binding, according to who it is being
established for, and must be one of the following two values.
GL_USER_KEY - The user requested this key-binding.
GL_APP_KEY - This is a default binding set by the
application.
When both user and application bindings for a given key-sequence have been specified, the
user binding takes precedence. The application's binding is subsequently reinstated if the
user's binding is later unbound via either another to this function, or a call to
gl_configure_getline().
The keyseq argument specifies the key-sequence to be bound or unbound, and is expressed in
the same way as in a ~/.teclarc configuration file. The action argument must either be a
string containing the name of the action to bind the key-sequence to, or it must be NULL
or "" to unbind the key-sequence.
CUSTOMIZED WORD COMPLETION
If in your application, you would like to have TAB completion complete other things in
addition to or instead of filenames, you can arrange this by registering an alternate
completion callback function, via a call to the gl_customize_completion() function.
int gl_customize_completion(GetLine *gl, void *data,
CplMatchFn *match_fn);
The data argument provides a way for your application to pass arbitrary, application-
specific information to the callback function. This is passed to the callback every time
that it is called. It might for example, point to the symbol table from which possible
completions are to be sought. The match_fn argument specifies the callback function to be
called. The CplMatchFn function type is defined in libtecla.h, as is a CPL_MATCH_FN()
macro that you can use to declare and prototype callback functions. The declaration and
responsibilities of callback functions are described in depth in the cpl_complete_word(3)
man page.
In brief, the callback function is responsible for looking backwards in the input line,
back from the point at which the user pressed TAB, to find the start of the word being
completed. It then must lookup possible completions of this word, and record them one by
one in the WordCompletion object that is passed to it as an argument, by calling the
cpl_add_completion() function. If the callback function wishes to provide filename
completion in addition to its own specific completions, it has the option of itself
calling the builtin file-name completion callback. This also, is documented in the
cpl_complete_word(3) man page.
Note that if you would like gl_get_line() to return the current input line when a
successful completion is been made, you can arrange this when you call
cpl_add_completion(), by making the last character of the continuation suffix a newline
character. If you do this, the input line will be updated to display the completion,
together with any contiuation suffix up to the newline character, then gl_get_line() will
return this input line.
If, for some reason, your callback function needs to write something to the terminal, it
must call gl_normal_io() before doing so. This will start a new line after the input line
that is currently being edited, reinstate normal terminal I/O, and tell gl_get_line() that
the input line will need to be redrawn when the callback returns.
ADDING COMPLETION ACTIONS
In the previous section the ability to customize the behavior of the only default
completion action, complete-word, was described. In this section the ability to install
additional action functions, so that different types of word completion can be bound to
different key-sequences, is described. This is achieved by using the
gl_completion_action() function.
int gl_completion_action(GetLine *gl,
void *data, CplMatchFn *match_fn,
int list_only, const char *name,
const char *keyseq);
The data and match_fn arguments are as described in the cpl_complete_word man page, and
specify the callback function that should be invoked to identify possible completions.
The list_only argument determines whether the action that is being defined should attempt
to complete the word as far as possible in the input line before displaying any possible
ambiguous completions, or whether it should simply display the list of possible
completions without touching the input line. The former option is selected by specifying a
value of 0, and the latter by specifying a value of 1. The name argument specifies the
name by which configuration files and future invocations of this function should refer to
the action. This must either be the name of an existing completion action to be changed,
or be a new unused name for a new action. Finally, the keyseq argument specifies the
default key-sequence to bind the action to. If this is NULL, no new keysequence will be
bound to the action.
Beware that in order for the user to be able to change the key-sequence that is bound to
actions that are installed in this manner, when you call gl_completion_action() to install
a given action for the first time, you should do this between calling new_GetLine() and
the first call to gl_get_line(). Otherwise, when the user's configuration file is read on
the first call to gl_get_line(), the name of the your additional action won't be known,
and any reference to it in the configuration file will generate an error.
As discussed for gl_customize_completion(), if your callback function, for some reason,
needs to write anything to the terminal, it must call gl_normal_io() before doing so.
DEFINING CUSTOM ACTIONS
Although the built-in key-binding actions are sufficient for the needs of most
applications, occasionally a specialized application may need to define one or more custom
actions, bound to application-specific key-sequences. For example, a sales application
would benefit from having a key-sequence that displayed the part name that corresponded to
a part number preceding the cursor. Such a feature is clearly beyond the scope of the
built-in action functions. So for such special cases, the gl_register_action() function is
provided.
int gl_register_action(GetLine *gl, void *data,
GlActionFn *fn, const char *name,
const char *keyseq);
This function lets the application register an external function, fn, that will thereafter
be called whenever either the specified key-sequence, keyseq, is entered by the user, or
the user enters any other key-sequence that the user subsequently binds to the specified
action name, name, in their configuration file. The data argument can be a pointer to
anything that the application wishes to have passed to the action function, fn, whenever
that function is invoked.
The action function, fn, should be declared using the following macro, which is defined in
libtecla.h.
#define GL_ACTION_FN(fn) GlAfterAction (fn)(GetLine *gl, \
void *data, int count, size_t curpos, \
const char *line)
The gl and data arguments are those that were previously passed to gl_register_action()
when the action function was registered. The count argument is a numeric argument which
the user has the option of entering using the digit-argument action, before invoking the
action. If the user doesn't enter a number, then the count argument is set to 1. Nominally
this argument is interpreted as a repeat count, meaning that the action should be repeated
that many times. In practice however, for some actions a repeat count makes little sense.
In such cases, actions can either simply ignore the count argument, or use its value for a
different purpose.
A copy of the current input line is passed in the read-only line argument. The current
cursor position within this string is given by the index contained in the curpos argument.
Note that direct manipulation of the input line and the cursor position is not permitted.
This is because the rules dicated by various modes, such as vi mode versus emacs mode, no-
echo mode, and insert mode versus overstrike mode etc, make it too complex for an
application writer to write a conforming editing action, as well as constrain future
changes to the internals of gl_get_line(). A potential solution to this dilema would be to
allow the action function to edit the line using the existing editing actions. This is
currently under consideration.
If the action function wishes to write text to the terminal, without this getting mixed up
with the displayed text of the input line, or read from the terminal without having to
handle raw terminal I/O, then before doing either of these operations, it must temporarily
suspend line editing by calling the gl_normal_io() function. This function flushes any
pending output to the terminal, moves the cursor to the start of the line that follows the
last terminal line of the input line, then restores the terminal to a state that is
suitable for use with the C stdio facilities. The latter includes such things as restoring
the normal mapping of \n to \r\n, and, when in server mode, restoring the normal blocking
form of terminal I/O. Having called this function, the action function can read from and
write to the terminal without the fear of creating a mess. It isn't necessary for the
action function to restore the original editing environment before it returns. This is
done automatically by gl_get_line() after the action function returns. The following is a
simple example of an action function which writes the sentence "Hello world" on a new
terminal line after the line being edited. When this function returns, the input line is
redrawn on the line that follows the "Hello world" line, and line editing resumes.
static GL_ACTION_FN(say_hello_fn)
{
if(gl_normal_io(gl)) /* Temporarily suspend editing */
return GLA_ABORT;
printf("Hello world\n");
return GLA_CONTINUE;
}
Action functions must return one of the following values, to tell gl_get_line() how to
procede.
GLA_ABORT - Cause gl_get_line() to return NULL.
GLA_RETURN - Cause gl_get_line() to return the
completed input line.
GLA_CONTINUE - Resume command-line editing.
Note that the name argument of gl_register_action() specifies the name by which a user can
refer to the action in their configuration file. This allows them to re-bind the action to
an alternate key-seqeunce. In order for this to work, it is necessary to call
gl_register_action() between calling new_GetLine() and the first call to gl_get_line().
HISTORY FILES
To save the contents of the history buffer before quitting your application, and
subsequently restore them when you next start the application, the following functions are
provided.
int gl_save_history(GetLine *gl, const char *filename,
const char *comment, int max_lines);
int gl_load_history(GetLine *gl, const char *filename,
const char *comment);
The filename argument specifies the name to give the history file when saving, or the name
of an existing history file, when loading. This may contain home-directory and environment
variable expressions, such as "~/.myapp_history" or "$HOME/.myapp_history".
Along with each history line, extra information about it, such as when it was entered by
the user, and what its nesting level is, is recorded as a comment preceding the line in
the history file. Writing this as a comment allows the history file to double as a command
file, just in case you wish to replay a whole session using it. Since comment prefixes
differ in different languages, the comment argument is provided for specifying the comment
prefix. For example, if your application were a unix shell, such as the bourne shell, you
would specify "#" here. Whatever you choose for the comment character, you must specify
the same prefix to gl_load_history() that you used when you called gl_save_history() to
write the history file.
The max_lines must be either -1 to specify that all lines in the history list be saved, or
a positive number specifying a ceiling on how many of the most recent lines should be
saved.
Both functions return non-zero on error, after writing an error message to stderr. Note
that gl_load_history() does not consider the non-existence of a file to be an error.
MULTIPLE HISTORY LISTS
If your application uses a single GetLine object for entering many different types of
input lines, you may wish gl_get_line() to distinguish the different types of lines in the
history list, and only recall lines that match the current type of line. To support this
requirement, gl_get_line() marks lines being recorded in the history list with an integer
identifier chosen by the application. Initially this identifier is set to 0 by
new_GetLine(), but it can be changed subsequently by calling gl_group_history().
int gl_group_history(GetLine *gl, unsigned id);
The integer identifier id can be any number chosen by the application, but note that
gl_save_history() and gl_load_history() preserve the association between identifiers and
historical input lines between program invocations, so you should choose fixed identifiers
for the different types of input line used by your application.
Whenever gl_get_line() appends a new input line to the history list, the current history
identifier is recorded with it, and when it is asked to recall a historical input line, it
only recalls lines that are marked with the current identifier.
DISPLAYING HISTORY
The history list can be displayed by calling gl_show_history().
int gl_show_history(GetLine *gl, FILE *fp,
const char *fmt,
int all_groups,
int max_lines);
This displays the current contents of the history list to the stdio output stream fp. If
the max_lines argument is greater than or equal to zero, then no more than this number of
the most recent lines will be displayed. If the all_groups argument is non-zero, lines
from all history groups are displayed. Otherwise just those of the currently selected
history group are displayed. The format string argument, fmt, determines how the line is
displayed. This can contain arbitrary characters which are written verbatim, interleaved
with any of the following format directives:
%D - The date on which the line was originally
entered, formatted like 2001-11-20.
%T - The time of day when the line was entered,
formatted like 23:59:59.
%N - The sequential entry number of the line in
the history buffer.
%G - The number of the history group which the
line belongs to.
%% - A literal % character.
%H - The history line itself.
Thus a format string like "%D %T %H0 would output something like:
2001-11-20 10:23:34 Hello world
Note the inclusion of an explicit newline character in the format string.
LOOKING UP HISTORY
The gl_lookup_history() function allows the calling application to look up lines in the
history list.
typedef struct {
const char *line; /* The requested historical */
/* line. */
unsigned group; /* The history group to which */
/* the line belongs. */
time_t timestamp; /* The date and time at which */
/* the line was originally */
/* entered. */
} GlHistoryLine;
int gl_lookup_history(GetLine *gl, unsigned long id,
GlHistoryLine *hline);
The id argument indicates which line to look up, where the first line that was entered in
the history list after new_GetLine() was called, is denoted by 0, and subsequently entered
lines are denoted with successively higher numbers. Note that the range of lines currently
preserved in the history list can be queried by calling the gl_range_of_history()
function, described later. If the requested line is in the history list, the details of
the line are recorded in the variable pointed to by the hline argument, and 1 is returned.
Otherwise 0 is returned, and the variable pointed to by hline is left unchanged.
Beware that the string returned in hline->line is part of the history buffer, so it must
not be modified by the caller, and will be recycled on the next call to any function that
takes gl as its argument. Therefore you should make a private copy of this string if you
need to keep it around.
MANUAL HISTORY ARCHIVAL
By default, whenever a line is entered by the user, it is automatically appended to the
history list, just before gl_get_line() returns the line to the caller. This is convenient
for the majority of applications, but there are also applications that need finer grained
control over what gets added to the history list. In such cases, the automatic addition of
entered lines to the history list can be turned off by calling the gl_automatic_history()
function.
int gl_automatic_history(GetLine *gl, int enable);
If this function is called with its enable argument set to 0, gl_get_line() won't
automatically archive subsequently entered lines. Automatic archiving can be re-enabled at
a later time, by calling this function again, with its enable argument set to 1. While
automatic history archiving is disabled, the calling application can use the
gl_append_history() to append lines to the history list as needed.
int gl_append_history(GetLine *gl, const char *line);
The line argument specifies the line to be added to the history list. This must be a
normal ' ' terminated string. If this string contains any newline characters, the line
that gets archived in the history list will be terminated by the first of these. Otherwise
it will be terminated by the ' ' terminator. If the line is longer than the maximum input
line length, that was specified when new_GetLine() was called, when the line is recalled,
it will get truncated to the actual gl_get_line() line length.
If successful, gl_append_history() returns 0. Otherwise it returns non-zero, and sets
errno to one of the following values.
EINVAL - One of the arguments passed to
gl_append_history() was NULL.
ENOMEM - The specified line was longer than the allocated
size of the history buffer (as specified when
new_GetLine() was called), so it couldn't be
archived.
A textual description of the error can optionally be obtained by calling
gl_error_message(). Note that after such an error, the history list remains in a valid
state to receive new history lines, so there is little harm in simply ignoring the return
status of gl_append_history().
MISCELLANEOUS HISTORY CONFIGURATION
If you wish to change the size of the history buffer that was originally specified in the
call to new_GetLine(), you can do so with the gl_resize_history() function.
int gl_resize_history(GetLine *gl, size_t histlen);
The histlen argument specifies the new size in bytes, and if you specify this as 0, the
buffer will be deleted.
As mentioned in the discussion of new_GetLine(), the number of lines that can be stored in
the history buffer, depends on the lengths of the individual lines. For example, a 1000
byte buffer could equally store 10 lines of average length 100 bytes, or 2 lines of
average length 50 bytes. Although the buffer is never expanded when new lines are added, a
list of pointers into the buffer does get expanded when needed to accommodate the number
of lines currently stored in the buffer. To place an upper limit on the number of lines in
the buffer, and thus a ceiling on the amount of memory used in this list, you can call the
gl_limit_history() function.
void gl_limit_history(GetLine *gl, int max_lines);
The max_lines should either be a positive number >= 0, specifying an upper limit on the
number of lines in the buffer, or be -1 to cancel any previously specified limit. When a
limit is in effect, only the max_lines most recently appended lines are kept in the
buffer. Older lines are discarded.
To discard lines from the history buffer, use the gl_clear_history() function.
void gl_clear_history(GetLine *gl, int all_groups);
The all_groups argument tells the function whether to delete just the lines associated
with the current history group (see gl_group_history()), or all historical lines in the
buffer.
The gl_toggle_history() function allows you to toggle history on and off without losing
the current contents of the history list.
void gl_toggle_history(GetLine *gl, int enable);
Setting the enable argument to 0 turns off the history mechanism, and setting it to 1
turns it back on. When history is turned off, no new lines will be added to the history
list, and history lookup key-bindings will act as though there is nothing in the history
buffer.
QUERYING HISTORY INFORMATION
The configured state of the history list can be queried with the gl_history_state()
function.
typedef struct {
int enabled; /* True if history is enabled */
unsigned group; /* The current history group */
int max_lines; /* The current upper limit on the */
/* number of lines in the history */
/* list, or -1 if unlimited. */
} GlHistoryState;
void gl_state_of_history(GetLine *gl,
GlHistoryState *state);
On return, the status information is recorded in the variable pointed to by the state
argument.
The gl_range_of_history() function returns the number and range of lines in the history
list.
typedef struct {
unsigned long oldest; /* The sequential entry number */
/* of the oldest line in the */
/* history list. */
unsigned long newest; /* The sequential entry number */
/* of the newest line in the */
/* history list. */
int nlines; /* The number of lines in the */
/* history list. */
} GlHistoryRange;
void gl_range_of_history(GetLine *gl, GlHistoryRange *range);
The return values are recorded in the variable pointed to by the range argument. If the
nlines member of this structure is greater than zero, then the oldest and newest members
report the range of lines in the list, and newest=oldest+nlines-1. Otherwise they are
both zero.
The gl_size_of_history() function returns the total size of the history buffer and the
amount of the buffer that is currently occupied.
typedef struct {
size_t size; /* The size of the history buffer */
/* (bytes). */
size_t used; /* The number of bytes of the */
/* history buffer that are */
/* currently occupied. */
} GlHistorySize;
void gl_size_of_history(GetLine *gl, GlHistorySize *size);
On return, the size information is recorded in the variable pointed to by the size
argument.
CHANGING TERMINALS
The new_GetLine() constructor function assumes that input is to be read from stdin, and
output written to stdout. The following function allows you to switch to different input
and output streams.
int gl_change_terminal(GetLine *gl, FILE *input_fp,
FILE *output_fp, const char *term);
The gl argument is the object that was returned by new_GetLine(). The input_fp argument
specifies the stream to read from, and output_fp specifies the stream to be written to.
Only if both of these refer to a terminal, will interactive terminal input be enabled.
Otherwise gl_get_line() will simply call fgets() to read command input. If both streams
refer to a terminal, then they must refer to the same terminal, and the type of this
terminal must be specified via the term argument. The value of the term argument is looked
up in the terminal information database (terminfo or termcap), in order to determine which
special control sequences are needed to control various aspects of the terminal.
new_GetLine() for example, passes the return value of getenv("TERM") in this argument.
Note that if one or both of input_fp and output_fp don't refer to a terminal, then it is
legal to pass NULL instead of a terminal type.
Note that if you want to pass file descriptors to gl_change_terminal(), you can do this by
creating stdio stream wrappers using the POSIX fdopen() function.
EXTERNAL EVENT HANDLING
By default, gl_get_line() doesn't return until either a complete input line has been
entered by the user, or an error occurs. In programs that need to watch for I/O from other
sources than the terminal, there are two options.
1. Use the functions described in the
gl_io_mode(3) man page to switch
gl_get_line() into non-blocking server mode. In this mode,
gl_get_line() becomes a non-blocking, incremental
line-editing function that can safely be called from
an external event loop. Although this is a very
versatile method, it involves taking on some
responsibilities that are normally performed behind
the scenes by gl_get_line().
2. While gl_get_line() is waiting for keyboard
input from the user, you can ask it to also watch for
activity on arbitrary file descriptors, such as
network sockets, pipes etc, and have it call functions
of your choosing when activity is seen. This works on
any system that has the select() system call,
which is most, if not all flavors of unix.
Registering a file descriptor to be watched by gl_get_line() involves calling the
gl_watch_fd() function.
int gl_watch_fd(GetLine *gl, int fd, GlFdEvent event,
GlFdEventFn *callback, void *data);
If this returns non-zero, then it means that either your arguments are invalid, or that
this facility isn't supported on the host system.
The fd argument is the file descriptor to be watched. The event argument specifies what
type of activity is of interest, chosen from the following enumerated values:
GLFD_READ - Watch for the arrival of data to be read.
GLFD_WRITE - Watch for the ability to write to the file
descriptor without blocking.
GLFD_URGENT - Watch for the arrival of urgent
out-of-band data on the file descriptor.
The callback argument is the function to call when the selected activity is seen. It
should be defined with the following macro, which is defined in libtecla.h.
#define GL_FD_EVENT_FN(fn) GlFdStatus (fn)(GetLine *gl, \
void *data, int fd, \
GlFdEvent event)
The data argument of the gl_watch_fd() function is passed to the callback function for its
own use, and can point to anything you like, including NULL. The file descriptor and the
event argument are also passed to the callback function, and this potentially allows the
same callback function to be registered to more than one type of event and/or more than
one file descriptor. The return value of the callback function should be one of the
following values.
GLFD_ABORT - Tell gl_get_line() to abort. When this
happens, gl_get_line() returns
NULL, and a following call to
gl_return_status() will return
GLR_FDABORT. Note that if the
application needs errno always to
have a meaningful value when
gl_get_line() returns NULL,
the callback function should set
errno appropriately.
GLFD_REFRESH - Redraw the input line then continue
waiting for input. Return this if
your callback wrote to the terminal.
GLFD_CONTINUE - Continue to wait for input, without
redrawing the line.
Note that before calling the callback, gl_get_line() blocks most signals, and leaves its
own signal handlers installed, so if you need to catch a particular signal you will need
to both temporarily install your own signal handler, and unblock the signal. Be sure to
re-block the signal (if it was originally blocked) and reinstate the original signal
handler, if any, before returning.
If the callback function needs to read or write to the terminal, it should ideally first
call gl_normal_io(gl) to temporarily suspend line editing. This will restore the terminal
to canonical, blocking-I/O, mode, and move the cursor to the start of a new terminal line.
Later, when the callback returns, gl_get_line() will notice that gl_normal_io() was
called, redisplay the input line and resume editing. Note that in this case the return
values, GLFD_REFRESH and GLFD_CONTINUE are equivalent.
To support cases where the callback function calls a third-party function which
o0cisire-enableddbeforeethetcallbacktfunctioneisecalled. Ifethetocallackonknowsonthat"0the
"
third-party function wrote to the terminal, it should then return the GLFD_REFRESH return
value, to tell gl_get_line() to redisplay the input line.
To remove a callback function that you previously registered for a given file descriptor
and event, simply call gl_watch_fd() with the same file descriptor and event arguments,
but with a callback argument of 0. The data argument is ignored in this case.
SETTING AN INACTIVITY TIMEOUT
On systems with the select() system call, the gl_inactivity_timeout() function can be used
to set or cancel an inactivity timeout. Inactivity in this case refers both to keyboard
input, and to I/O on any file descriptors registered by prior and subsequent calls to
gl_watch_fd(). On oddball systems that don't have select(), this call has no effect.
int gl_inactivity_timeout(GetLine *gl, GlTimeoutFn *callback,
void *data, unsigned long sec,
unsigned long nsec);
The timeout is specified in the form of an integral number of seconds and an integral
number of nanoseconds, via the sec and nsec arguments respectively. Subsequently, whenever
no activity is seen for this time period, the function specified via the callback argument
is called. The data argument of gl_inactivity_timeout() is passed verbatim to this
callback function whenever it is invoked, and can thus be used to pass arbitrary
application-specific information to the callback. The following macro is provided in
libtecla.h for applications to use to declare and prototype timeout callback functions.
#define GL_TIMEOUT_FN(fn) \
GlAfterTimeout (fn)(GetLine *gl, void *data)
On returning, the application's callback is expected to return one of the following
enumerators to tell gl_get_line() how to procede after the timeout has been handled by the
callback.
GLTO_ABORT - Tell gl_get_line() to abort. When
this happens, gl_get_line() will
return NULL, and a following call
to gl_return_status() will return
GLR_TIMEOUT. Note that if the
application needs errno always to
have a meaningful value when
gl_get_line() returns NULL,
the callback function should set
errno appropriately.
GLTO_REFRESH - Redraw the input line, then continue
waiting for input. You should return
this value if your callback wrote to the
terminal without having first called
gl_normal_io(gl).
GLTO_CONTINUE - In normal blocking-I/O mode, continue to
wait for input, without redrawing the
user's input line.
In non-blocking server I/O mode (see
gl_io_mode(3)), cause gl_get_line()
to act as though I/O blocked. This means
that gl_get_line() will immediately
return NULL, and a following call
to gl_return_status() will return
GLR_BLOCKED.
Note that before calling the callback, gl_get_line() blocks most signals, and leaves its
own signal handlers installed, so if you need to catch a particular signal you will need
to both temporarily install your own signal handler, and unblock the signal. Be sure to
re-block the signal (if it was originally blocked) and reinstate the original signal
handler, if any, before returning.
If the callback function needs to read or write to the terminal, it should ideally first
call gl_normal_io(gl) to temporarily suspend line editing. This will restore the terminal
to canonical, blocking-I/O, mode, and move the cursor to the start of a new terminal line.
Later, when the callback returns, gl_get_line() will notice that gl_normal_io() was
called, redisplay the input line and resume editing. Note that in this case the return
values, GLTO_REFRESH and GLTO_CONTINUE are equivalent.
To support cases where the callback function calls a third-party function which
o0cisire-enableddbeforeethetcallbacktfunctioneisecalled. Ifethetocallackonknowsonthat"0the
"
third-party function wrote to the terminal, it should then return the GLTO_REFRESH return
value, to tell gl_get_line() to redisplay the input line.
Note that although the timeout argument includes a nano-second component, few computer
clocks presently have resolutions that are finer than a few milliseconds, so asking for
less than a few milliseconds is equivalent to requesting zero seconds on a lot of systems.
If this would be a problem, you should base your timeout selection on the actual
resolution of the host clock (eg. by calling sysconf(_SC_CLK_TCK)).
To turn off timeouts, simply call gl_inactivity_timeout() with a callback argument of 0.
The data argument is ignored in this case.
SIGNAL HANDLING DEFAULTS
By default, the gl_get_line() function intercepts a number of signals. This is
particularly important for signals which would by default terminate the process, since the
terminal needs to be restored to a usable state before this happens. In this section, the
signals that are trapped by default, and how gl_get_line() responds to them, is described.
Changing these defaults is the topic of the following section.
When the following subset of signals are caught, gl_get_line() first restores the terminal
settings and signal handling to how they were before gl_get_line() was called, resends the
signal, to allow the calling application's signal handlers to handle it, then if the
process still exists, gl_get_line() returns NULL and sets errno as specified below.
SIGINT - This signal is generated both by the keyboard
interrupt key (usually ^C), and the keyboard
break key.
errno=EINTR
SIGHUP - This signal is generated when the controlling
terminal exits.
errno=ENOTTY
SIGPIPE - This signal is generated when a program attempts
to write to a pipe who's remote end isn't being
read by any process. This can happen for example
if you have called gl_change_terminal() to
redirect output to a pipe hidden under a pseudo
terminal.
errno=EPIPE
SIGQUIT - This signal is generated by the keyboard quit
key (usually ^\).
errno=EINTR
SIGABRT - This signal is generated by the standard C,
abort() function. By default it both
terminates the process and generates a core
dump.
errno=EINTR
SIGTERM - This is the default signal that the UN*X
kill command sends to processes.
errno=EINTR
Note that in the case of all of the above signals, POSIX mandates that by default the
process is terminated, with the addition of a core dump in the case of the SIGQUIT signal.
In other words, if the calling application doesn't override the default handler by
supplying its own signal handler, receipt of the corresponding signal will terminate the
application before gl_get_line() returns.
If gl_get_line() aborts with errno set to EINTR, you can find out what signal caused it to
abort, by calling the following function.
int gl_last_signal(const GetLine *gl);
This returns the numeric code (eg. SIGINT) of the last signal that was received during the
most recent call to gl_get_line(), or -1 if no signals were received.
On systems that support it, when a SIGWINCH (window change) signal is received,
gl_get_line() queries the terminal to find out its new size, redraws the current input
line to accommodate the new size, then returns to waiting for keyboard input from the
user. Unlike other signals, this signal isn't resent to the application.
Finally, the following signals cause gl_get_line() to first restore the terminal and
signal environment to that which prevailed before gl_get_line() was called, then resend
the signal to the application. If the process still exists after the signal has been
delivered, then gl_get_line() then re-establishes its own signal handlers, switches the
terminal back to raw mode, redisplays the input line, and goes back to awaiting terminal
input from the user.
SIGCONT - This signal is generated when a suspended
process is resumed.
SIGPOLL - On SVR4 systems, this signal notifies the
process of an asynchronous I/O event. Note
that under 4.3+BSD, SIGIO and SIGPOLL are
the same. On other systems, SIGIO is ignored
by default, so gl_get_line() doesn't
trap it by default.
SIGPWR - This signal is generated when a power failure
occurs (presumably when the system is on a
UPS).
SIGALRM - This signal is generated when a timer
expires.
SIGUSR1 - An application specific signal.
SIGUSR2 - Another application specific signal.
SIGVTALRM - This signal is generated when a virtual
timer expires (see man setitimer(2)).
SIGXCPU - This signal is generated when a process
exceeds its soft CPU time limit.
SIGXFSZ - This signal is generated when a process
exceeds its soft file-size limit.
SIGTSTP - This signal is generated by the terminal
suspend key, which is usually ^Z, or the
delayed terminal suspend key, which is
usually ^Y.
SIGTTIN - This signal is generated if the program
attempts to read from the terminal while the
program is running in the background.
SIGTTOU - This signal is generated if the program
attempts to write to the terminal while the
program is running in the background.
Obviously not all of the above signals are supported on all systems, so code to support
them is conditionally compiled into the tecla library.
Note that if SIGKILL or SIGPOLL, which by definition can't be caught, or any of the
hardware generated exception signals, such as SIGSEGV, SIGBUS and SIGFPE, are received and
unhandled while gl_get_line() has the terminal in raw mode, the program will be terminated
without the terminal having been restored to a usable state. In practice, job-control
shells usually reset the terminal settings when a process relinquishes the controlling
terminal, so this is only a problem with older shells.
CUSTOMIZED SIGNAL HANDLING
The previous section listed the signals that gl_get_line() traps by default, and described
how it responds to them. This section describes how to both add and remove signals from
the list of trapped signals, and how to specify how gl_get_line() should respond to a
given signal.
If you don't need gl_get_line() to do anything in response to a signal that it normally
traps, you can tell to gl_get_line() to ignore that signal by calling gl_ignore_signal().
int gl_ignore_signal(GetLine *gl, int signo);
The signo argument is the number of the signal (eg. SIGINT) that you want to have ignored.
If the specified signal isn't currently one of those being trapped, this function does
nothing.
The gl_trap_signal() function allows you to either add a new signal to the list that
gl_get_line() traps, or modify how it responds to a signal that it already traps.
int gl_trap_signal(GetLine *gl, int signo, unsigned flags,
GlAfterSignal after, int errno_value);
The signo argument is the number of the signal that you wish to have trapped. The flags
argument is a set of flags which determine the environment in which the application's
signal handler is invoked, the after argument tells gl_get_line() what to do after the
application's signal handler returns, and errno_value tells gl_get_line() what to set
errno to if told to abort.
The flags argument is a bitwise OR of zero or more of the following enumerators:
GLS_RESTORE_SIG - Restore the caller's signal
environment while handling the
signal.
GLS_RESTORE_TTY - Restore the caller's terminal settings
while handling the signal.
GLS_RESTORE_LINE - Move the cursor to the start of the
line following the input line before
invoking the application's signal
handler.
GLS_REDRAW_LINE - Redraw the input line when the
application's signal handler returns.
GLS_UNBLOCK_SIG - Normally, if the calling program has
a signal blocked (man sigprocmask),
gl_get_line() does not trap that
signal. This flag tells gl_get_line()
to trap the signal and unblock it for
the duration of the call to
gl_get_line().
GLS_DONT_FORWARD - If this flag is included, the signal
will not be forwarded to the signal
handler of the calling program.
Two commonly useful flag combinations are also enumerated as follows:
GLS_RESTORE_ENV = GLS_RESTORE_SIG | GLS_RESTORE_TTY |
GLS_REDRAW_LINE
GLS_SUSPEND_INPUT = GLS_RESTORE_ENV | GLS_RESTORE_LINE
If your signal handler, or the default system signal handler for this signal, if you
haven't overridden it, never either writes to the terminal, nor suspends or terminates the
calling program, then you can safely set the flags argument to 0.
If your signal handler always writes to the terminal, reads from it, or suspends or
terminates the program, you should specify the flags argument as GL_SUSPEND_INPUT, so
that:
1. The cursor doesn't get left in the middle of the input
line.
2. So that the user can type in input and have it echoed.
3. So that you don't need to end each output line with
\r\n, instead of just \n.
The GL_RESTORE_ENV combination is the same as GL_SUSPEND_INPUT, except that it doesn't
move the cursor, and if your signal handler doesn't read or write anything to the
terminal, the user won't see any visible indication that a signal was caught. This can be
useful if you have a signal handler that only occasionally writes to the terminal, where
using GL_SUSPEND_LINE would cause the input line to be unnecessarily duplicated when
nothing had been written to the terminal. Such a signal handler, when it does write to
the terminal, should be sure to start a new line at the start of its first write, by
writing a \n character, and should be sure to leave the cursor on a new line before
returning. If the signal arrives while the user is entering a line that only occupies a
signal terminal line, or if the cursor is on the last terminal line of a longer input
line, this will have the same effect as GL_SUSPEND_INPUT. Otherwise it will start writing
on a line that already contains part of the displayed input line. This doesn't do any
harm, but it looks a bit ugly, which is why the GL_SUSPEND_INPUT combination is better if
you know that you are always going to be writing to the terminal.
The after argument, which determines what gl_get_line() does after the application's
signal handler returns (if it returns), can take any one of the following values:
GLS_RETURN - Return the completed input line, just as
though the user had pressed the return
key.
GLS_ABORT - Cause gl_get_line() to abort. When
this happens, gl_get_line() returns
NULL, and a following call to
gl_return_status() will return
GLR_SIGNAL. Note that if the
application needs errno always to
have a meaningful value when
gl_get_line() returns NULL,
the callback function should set
errno appropriately.
GLS_CONTINUE - Resume command line editing.
The errno_value argument is intended to be combined with the GLS_ABORT option, telling
gl_get_line() what to set the standard errno variable to before returning NULL to the
calling program. It can also, however, be used with the GL_RETURN option, in case you wish
to have a way to distinguish between an input line that was entered using the return key,
and one that was entered by the receipt of a signal.
RELIABLE SIGNAL HANDLING
Signal handling is suprisingly hard to do reliably without race conditions. In
gl_get_line() a lot of care has been taken to allow applications to perform reliable
signal handling around gl_get_line(). This section explains how to make use of this.
As an example of the problems that can arise if the application isn't written correctly,
imagine that one's application has a SIGINT signal handler that sets a global flag. Now
suppose that the application tests this flag just before invoking gl_get_line(). If a
SIGINT signal happens to be received in the small window of time between the statement
that tests the value of this flag, and the statement that calls gl_get_line(), then
gl_get_line() will not see the signal, and will not be interrupted. As a result, the
application won't be able to respond to the signal until the user gets around to finishing
entering the input line and gl_get_line() returns. Depending on the application, this
might or might not be a disaster, but at the very least it would puzzle the user.
The way to avoid such problems is to do the following.
1. If needed, use the gl_trap_signal() function to
configure gl_get_line() to abort when important
signals are caught.
2. Configure gl_get_line() such that if any of the
signals that it catches are blocked when
gl_get_line() is called, they will be unblocked
automatically during times when gl_get_line() is
waiting for I/O. This can be done either
on a per signal basis, by calling the
gl_trap_signal() function, and specifying the
GLS_UNBLOCK attribute of the signal, or globally by
calling the gl_catch_blocked() function.
void gl_catch_blocked(GetLine *gl);
This function simply adds the GLS_UNBLOCK attribute
to all of the signals that it is currently configured to
trap.
3. Just before calling gl_get_line(), block delivery
of all of the signals that gl_get_line() is
configured to trap. This can be done using the POSIX
sigprocmask() function in conjunction with the
gl_list_signals() function.
int gl_list_signals(GetLine *gl, sigset_t *set);
This function returns the set of signals that it is
currently configured to catch in the set argument,
which is in the form required by sigprocmask().
4. In the example, one would now test the global flag that
the signal handler sets, knowing that there is now no
danger of this flag being set again until
gl_get_line() unblocks its signals while performing
I/O.
5. Eventually gl_get_line() returns, either because
a signal was caught, an error occurred, or the user
finished entering their input line.
6. Now one would check the global signal flag again, and if
it is set, respond to it, and zero the flag.
7. Use sigprocmask() to unblock the signals that were
blocked in step 3.
The same technique can be used around certain POSIX signal-aware functions, such as
sigsetjmp() and sigsuspend(), and in particular, the former of these two functions can be
used in conjunction with siglongjmp() to implement race-condition free signal handling
around other long-running system calls. The way to do this, is explained next, by showing
how gl_get_line() manages to reliably trap signals around calls to functions like read()
and select() without race conditions.
The first thing that gl_get_line() does, whenever it is called, is to use the POSIX
sigprocmask() function to block the delivery of all of the signals that it is currently
configured to catch. This is redundant if the application has already blocked them, but it
does no harm. It undoes this step just before returning.
Whenever gl_get_line() needs to call read() or select() to wait for input from the user,
it first calls the POSIX sigsetjmp() function, being sure to specify a non-zero value for
its savesigs argument. The reason for the latter argument will become clear shortly.
If sigsetjmp() returns zero, gl_get_line() then does the following.
a. It uses the POSIX sigaction() function to register
a temporary signal handler to all of the signals that it
is configured to catch. This signal handler does two
things.
1. It records the number of the signal that was received
in a file-scope variable.
2. It then calls the POSIX siglongjmp()
function using the buffer that was passed to
sigsetjmp() for its first argument, and
a non-zero value for its second argument.
When this signal handler is registered, the sa_mask
member of the struct sigaction act argument of the
call to sigaction() is configured to contain all of
the signals that gl_get_line() is catching. This
ensures that only one signal will be caught at once by
our signal handler, which in turn ensures that multiple
instances of our signal handler don't tread on each
other's toes.
b. Now that the signal handler has been set up,
gl_get_line() unblocks all of the signals that it
is configured to catch.
c. It then calls the read() or select() system
calls to wait for keyboard input.
d. If this system call returns (ie. no signal is received),
gl_get_line() blocks delivery of the signals of
interest again.
e. It then reinstates the signal handlers that were
displaced by the one that was just installed.
Alternatively, if sigsetjmp() returns non-zero, this means that one of the signals being
trapped was caught while the above steps were executing. When this happens, gl_get_line()
does the following.
First, note that when a call to siglongjmp() causes sigsetjmp() to return, provided that
the savesigs argument of sigsetjmp() was non-zero, as specified above, the signal process
mask is restored to how it was when sigsetjmp() was called. This is the important
difference between sigsetjmp() and the older problematic setjmp(), and is the essential
ingredient that makes it possible to avoid signal handling race conditions. Because of
this we are guaranteed that all of the signals that we blocked before calling sigsetjmp()
are blocked again as soon as any signal is caught. The following statements, which are
then executed, are thus guaranteed to be executed without any further signals being
caught.
1. If so instructed by the gl_get_line() configuration
attributes of the signal that was caught,
gl_get_line() restores the terminal attributes to
the state that they had when gl_get_line() was
called. This is particularly important for signals that
suspend or terminate the process, since otherwise the
terminal would be left in an unusable state.
2. It then reinstates the application's signal handlers.
3. Then it uses the C standard-library raise()
function to re-send the application the signal that
was caught.
3. Next it unblocks delivery of the signal that we just
sent. This results in the signal that was just sent
via raise(), being caught by the application's
original signal handler, which can now handle it as it
sees fit.
4. If the signal handler returns (ie. it doesn't terminate
the process), gl_get_line() blocks delivery of the
above signal again.
5. It then undoes any actions performed in the first of the
above steps, and redisplays the line, if the signal
configuration calls for this.
6. gl_get_line() then either resumes trying to
read a character, or aborts, depending on the
configuration of the signal that was caught.
What the above steps do in essence is to take asynchronously delivered signals and handle
them synchronously, one at a time, at a point in the code where gl_get_line() has complete
control over its environment.
THE TERMINAL SIZE
On most systems the combination of the TIOCGWINSZ ioctl and the SIGWINCH signal is used to
maintain an accurate idea of the terminal size. The terminal size is newly queried every
time that gl_get_line() is called and whenever a SIGWINCH signal is received.
On the few systems where this mechanism isn't available, at startup new_GetLine() first
looks for the LINES and COLUMNS environment variables. If these aren't found, or they
contain unusable values, then if a terminal information database like terminfo or termcap
is available, the default size of the terminal is looked up in this database. If this too
fails to provide the terminal size, a default size of 80 columns by 24 lines is used.
Even on systems that do support ioctl(TIOCGWINSZ), if the terminal is on the other end of
a serial line, the terminal driver generally has no way of detecting when a resize occurs
or of querying what the current size is. In such cases no SIGWINCH is sent to the process,
and the dimensions returned by ioctl(TIOCGWINSZ) aren't correct. The only way to handle
such instances is to provide a way for the user to enter a command that tells the remote
system what the new size is. This command would then call the gl_set_term_size() function
to tell gl_get_line() about the change in size.
int gl_set_term_size(GetLine *gl, int ncolumn, int nline);
The ncolumn and nline arguments are used to specify the new dimensions of the terminal,
and must not be less than 1. On systems that do support ioctl(TIOCGWINSZ), this function
first calls ioctl(TIOCSWINSZ) to tell the terminal driver about the change in size. In
non-blocking server-I/O mode, if a line is currently being input, the input line is then
redrawn to accommodate the changed size. Finally the new values are recorded in gl for
future use by gl_get_line().
The gl_terminal_size() function allows you to query the current size of the terminal, and
install an alternate fallback size for cases where the size isn't available. Beware that
the terminal size won't be available if reading from a pipe or a file, so the default
values can be important even on systems that do support ways of finding out the terminal
size.
typedef struct {
int nline; /* The terminal has nline lines */
int ncolumn; /* The terminal has ncolumn columns */
} GlTerminalSize;
GlTerminalSize gl_terminal_size(GetLine *gl,
int def_ncolumn,
int def_nline);
This function first updates gl_get_line()'s fallback terminal dimensions, then records its
findings in the return value.
The def_ncolumn and def_nline specify the default number of terminal columns and lines to
use if the terminal size can't be determined via ioctl(TIOCGWINSZ) or environment
variables.
HIDING WHAT YOU TYPE
When entering sensitive information, such as passwords, it is best not to have the text
that you are entering echoed on the terminal. Furthermore, such text should not be
recorded in the history list, since somebody finding your terminal unattended could then
recall it, or somebody snooping through your directories could see it in your history
file. With this in mind, the gl_echo_mode() function allows you to toggle on and off the
display and archival of any text that is subsequently entered in calls to gl_get_line().
int gl_echo_mode(GetLine *gl, int enable);
The enable argument specifies whether entered text should be visible or not. If it is 0,
then subsequently entered lines will not be visible on the terminal, and will not be
recorded in the history list. If it is 1, then subsequent input lines will be displayed as
they are entered, and provided that history hasn't been turned off via a call to
gl_toggle_history(), then they will also be archived in the history list. Finally, if the
enable argument is -1, then the echoing mode is left unchanged, which allows you to non-
destructively query the current setting via the return value. In all cases, the return
value of the function is 0 if echoing was disabled before the function was called, and 1
if it was enabled.
When echoing is turned off, note that although tab completion will invisibly complete your
prefix as far as possible, ambiguous completions will not be displayed.
SINGLE CHARACTER QUERIES
Using gl_get_line() to query the user for a single character reply, is inconvenient for
the user, since they must hit the enter or return key before the character that they typed
is returned to the program. Thus the gl_query_char() function has been provided for single
character queries like this.
int gl_query_char(GetLine *gl, const char *prompt,
char defchar);
This function displays the specified prompt at the start of a new line, and waits for the
user to type a character. When the user types a character, gl_query_char() displays it to
the right of the prompt, starts a newline, then returns the character to the calling
program. The return value of the function is the character that was typed. If the read had
to be aborted for some reason, EOF is returned instead. In the latter case, the
application can call the previously documented gl_return_status(), to find out what went
wrong. This could, for example, have been the reception of a signal, or the optional
inactivity timer going off.
If the user simply hits enter, the value of the defchar argument is substituted. This
means that when the user hits either newline or return, the character specified in
defchar, is displayed after the prompt, as though the user had typed it, as well as being
returned to the calling application. If such a replacement is not important, simply pass
'0 as the value of defchar.
If the entered character is an unprintable character, it is displayed symbolically. For
example, control-A is displayed as ^A, and characters beyond 127 are displayed in octal,
preceded by a backslash.
As with gl_get_line(), echoing of the entered character can be disabled using the
gl_echo_mode() function.
If the calling process is suspended while waiting for the user to type their response, the
cursor is moved to the line following the prompt line, then when the process resumes, the
prompt is redisplayed, and gl_query_char() resumes waiting for the user to type a
character.
Note that in non-blocking server mode, (see gl_io_mode(3)), if an incomplete input line is
in the process of being read when gl_query_char() is called, the partial input line is
discarded, and erased from the terminal, before the new prompt is displayed. The next call
to gl_get_line() will thus start editing a new line.
READING RAW CHARACTERS
Whereas the gl_query_char() function visibly prompts the user for a character, and
displays what they typed, the gl_read_char() function reads a signal character from the
user, without writing anything to the terminal, or perturbing any incompletely entered
input line. This means that it can be called not only from between calls to gl_get_line(),
but also from callback functions that the application has registered to be called by
gl_get_line().
int gl_read_char(GetLine *gl);
On success, the return value of gl_read_char() is the character that was read. On failure,
EOF is returned, and the gl_return_status() function can be called to find out what went
wrong. Possibilities include the optional inactivity timer going off, the receipt of a
signal that is configured to abort gl_get_line(), or terminal I/O blocking, when in non-
blocking server-I/O mode.
Beware that certain keyboard keys, such as function keys, and cursor keys, usually
generate at least 3 characters each, so a single call to gl_read_char() won't be enough to
identify such keystrokes.
CLEARING THE TERMINAL
The calling program can clear the terminal by calling gl_erase_terminal(). In non-blocking
server-I/O mode, this function also arranges for the current input line to be redrawn from
scratch when gl_get_line() is next called.
int gl_erase_terminal(GetLine *gl);
DISPLAYING TEXT DYNAMICALLY
Between calls to gl_get_line(), the gl_display_text() function provides a convenient way
to display paragraphs of text, left-justified and split over one or more terminal lines
according to the constraints of the current width of the terminal. Examples of the use of
this function may be found in the demo programs, where it is used to display
introductions. In those examples the advanced use of optional prefixes, suffixes and
filled lines to draw a box around the text is also illustrated.
int gl_display_text(GetLine *gl, int indentation,
const char *prefix,
const char *suffix, int fill_char,
int def_width, int start,
const char *string);
If gl isn't currently connected to a terminal, for example if the output of a program that
uses gl_get_line() is being piped to another program or redirected to a file, then the
value of the def_width parameter is used as the terminal width.
The indentation argument specifies the number of characters to use to indent each line of
output. The fill_char argument specifies the character that will be used to perform this
indentation.
The prefix argument can either be NULL, or be a string to place at the beginning of each
new line (after any indentation). Similarly, the suffix argument can either be NULL, or
be a string to place at the end of each line. The suffix is placed flush against the right
edge of the terminal, and any space between its first character and the last word on that
line is filled with the character specified via the fill_char argument. Normally the
fill-character is a space.
The start argument tells gl_display_text() how many characters have already been written
to the current terminal line, and thus tells it the starting column index of the cursor.
Since the return value of gl_display_text() is the ending column index of the cursor, by
passing the return value of one call to the start argument of the next call, a paragraph
that is broken between more than one string can be composed by calling gl_display_text()
for each successive portion of the paragraph. Note that literal newline characters are
necessary at the end of each paragraph to force a new line to be started.
On error, gl_display_text() returns -1.
CALLBACK FUNCTION FACILITIES
Unless otherwise stated, callback functions, such as tab completion callbacks and event
callbacks should not call any functions in this module. The following functions, however,
are designed specifically to be used by callback functions.
Calling the gl_replace_prompt() function from a callback tells gl_get_line() to display a
different prompt when the callback returns. Except in non-blocking server mode, it has no
effect if used between calls to gl_get_line(). In non-blocking server mode (see the
gl_io_mode(3) man page, when used between two calls to gl_get_line() that are operating on
the same input line, the current input line will be re-drawn with the new prompt on the
following call to gl_get_line().
void gl_replace_prompt(GetLine *gl, const char *prompt);
INTERNATIONAL CHARACTER SETS
Since libtecla version 1.4.0, gl_get_line() has been 8-bit clean. This means that all
8-bit characters that are printable in the user's current locale are now displayed
verbatim and included in the returned input line. Assuming that the calling program
correctly contains a call like the following,
setlocale(LC_CTYPE, "");
then the current locale is determined by the first of the environment variables LC_CTYPE,
LC_ALL, and LANG, that is found to contain a valid locale name. If none of these variables
are defined, or the program neglects to call setlocale, then the default C locale is used,
which is US 7-bit ASCII. On most unix-like platforms, you can get a list of valid locales
by typing the command:
locale -a
at the shell prompt. Further documentation on how the user can make use of this to enter
international characters can be found in the tecla(7) man page.
THREAD SAFETY
In a multi-threaded program, you should use the libtecla_r.a version of the library. This
uses reentrant versions of system functions, where available. Unfortunately neither
terminfo nor termcap were designed to be reentrant, so you can't safely use the functions
of the getline module in multiple threads (you can use the separate file-expansion and
word-completion modules in multiple threads, see the corresponding man pages for details).
However due to the use of POSIX reentrant functions for looking up home directories etc,
it is safe to use this module from a single thread of a multi-threaded program, provided
that your other threads don't use any termcap or terminfo functions.
FILES
libtecla.a - The tecla library
libtecla.h - The tecla header file.
~/.teclarc - The personal tecla customization file.
SEE ALSO
libtecla(3), gl_io_mode(3), tecla(7), ef_expand_file(3),
cpl_complete_word(3), pca_lookup_file(3)
AUTHOR
Martin Shepherd (mcs@astro.caltech.edu)
gl_get_line(3)