Provided by: libtecla-dev_1.6.3-3.1build1_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 f0ncisonre-enabledasbeforey the
unpredictably writes to the terminal, the automatic conversion of "0 to "
callback function is called. If the callack knows that the third-party function wrote to the terminal, it
should then return the GLFD_REFRESH return value, to tell gl_get_line() to redisplay the input line.
To remove a callback function that you previously registered for a given file descriptor and event,
simply call gl_watch_fd() with the same file descriptor and event arguments, but with a callback argument
of 0. The data argument is ignored in this case.
SETTING AN INACTIVITY TIMEOUT
On systems with the select() system call, the gl_inactivity_timeout() function can be used to set or
cancel an inactivity timeout. Inactivity in this case refers both to keyboard input, and to I/O on any
file descriptors registered by prior and subsequent calls to gl_watch_fd(). On oddball systems that don't
have select(), this call has no effect.
int gl_inactivity_timeout(GetLine *gl, GlTimeoutFn *callback,
void *data, unsigned long sec,
unsigned long nsec);
The timeout is specified in the form of an integral number of seconds and an integral number of
nanoseconds, via the sec and nsec arguments respectively. Subsequently, whenever no activity is seen for
this time period, the function specified via the callback argument is called. The data argument of
gl_inactivity_timeout() is passed verbatim to this callback function whenever it is invoked, and can thus
be used to pass arbitrary application-specific information to the callback. The following macro is
provided in libtecla.h for applications to use to declare and prototype timeout callback functions.
#define GL_TIMEOUT_FN(fn) \
GlAfterTimeout (fn)(GetLine *gl, void *data)
On returning, the application's callback is expected to return one of the following enumerators to tell
gl_get_line() how to procede after the timeout has been handled by the callback.
GLTO_ABORT - Tell gl_get_line() to abort. When
this happens, gl_get_line() will
return NULL, and a following call
to gl_return_status() will return
GLR_TIMEOUT. Note that if the
application needs errno always to
have a meaningful value when
gl_get_line() returns NULL,
the callback function should set
errno appropriately.
GLTO_REFRESH - Redraw the input line, then continue
waiting for input. You should return
this value if your callback wrote to the
terminal without having first called
gl_normal_io(gl).
GLTO_CONTINUE - In normal blocking-I/O mode, continue to
wait for input, without redrawing the
user's input line.
In non-blocking server I/O mode (see
gl_io_mode(3)), cause gl_get_line()
to act as though I/O blocked. This means
that gl_get_line() will immediately
return NULL, and a following call
to gl_return_status() will return
GLR_BLOCKED.
Note that before calling the callback, gl_get_line() blocks most signals, and leaves its own signal
handlers installed, so if you need to catch a particular signal you will need to both temporarily install
your own signal handler, and unblock the signal. Be sure to re-block the signal (if it was originally
blocked) and reinstate the original signal handler, if any, before returning.
If the callback function needs to read or write to the terminal, it should ideally first call
gl_normal_io(gl) to temporarily suspend line editing. This will restore the terminal to canonical,
blocking-I/O, mode, and move the cursor to the start of a new terminal line. Later, when the callback
returns, gl_get_line() will notice that gl_normal_io() was called, redisplay the input line and resume
editing. Note that in this case the return values, GLTO_REFRESH and GLTO_CONTINUE are equivalent.
To support cases where the callback function calls a third-party f0ncisonre-enabledasbeforey the
unpredictably writes to the terminal, the automatic conversion of "0 to "
callback function is called. If the callack knows that the third-party function wrote to the terminal, it
should then return the GLTO_REFRESH return value, to tell gl_get_line() to redisplay the input line.
Note that although the timeout argument includes a nano-second component, few computer clocks presently
have resolutions that are finer than a few milliseconds, so asking for less than a few milliseconds is
equivalent to requesting zero seconds on a lot of systems. If this would be a problem, you should base
your timeout selection on the actual resolution of the host clock (eg. by calling sysconf(_SC_CLK_TCK)).
To turn off timeouts, simply call gl_inactivity_timeout() with a callback argument of 0. The data
argument is ignored in this case.
SIGNAL HANDLING DEFAULTS
By default, the gl_get_line() function intercepts a number of signals. This is particularly important for
signals which would by default terminate the process, since the terminal needs to be restored to a usable
state before this happens. In this section, the signals that are trapped by default, and how
gl_get_line() responds to them, is described. Changing these defaults is the topic of the following
section.
When the following subset of signals are caught, gl_get_line() first restores the terminal settings and
signal handling to how they were before gl_get_line() was called, resends the signal, to allow the
calling application's signal handlers to handle it, then if the process still exists, gl_get_line()
returns NULL and sets errno as specified below.
SIGINT - This signal is generated both by the keyboard
interrupt key (usually ^C), and the keyboard
break key.
errno=EINTR
SIGHUP - This signal is generated when the controlling
terminal exits.
errno=ENOTTY
SIGPIPE - This signal is generated when a program attempts
to write to a pipe who's remote end isn't being
read by any process. This can happen for example
if you have called gl_change_terminal() to
redirect output to a pipe hidden under a pseudo
terminal.
errno=EPIPE
SIGQUIT - This signal is generated by the keyboard quit
key (usually ^\).
errno=EINTR
SIGABRT - This signal is generated by the standard C,
abort() function. By default it both
terminates the process and generates a core
dump.
errno=EINTR
SIGTERM - This is the default signal that the UN*X
kill command sends to processes.
errno=EINTR
Note that in the case of all of the above signals, POSIX mandates that by default the process is
terminated, with the addition of a core dump in the case of the SIGQUIT signal. In other words, if the
calling application doesn't override the default handler by supplying its own signal handler, receipt of
the corresponding signal will terminate the application before gl_get_line() returns.
If gl_get_line() aborts with errno set to EINTR, you can find out what signal caused it to abort, by
calling the following function.
int gl_last_signal(const GetLine *gl);
This returns the numeric code (eg. SIGINT) of the last signal that was received during the most recent
call to gl_get_line(), or -1 if no signals were received.
On systems that support it, when a SIGWINCH (window change) signal is received, gl_get_line() queries the
terminal to find out its new size, redraws the current input line to accommodate the new size, then
returns to waiting for keyboard input from the user. Unlike other signals, this signal isn't resent to
the application.
Finally, the following signals cause gl_get_line() to first restore the terminal and signal environment
to that which prevailed before gl_get_line() was called, then resend the signal to the application. If
the process still exists after the signal has been delivered, then gl_get_line() then re-establishes its
own signal handlers, switches the terminal back to raw mode, redisplays the input line, and goes back to
awaiting terminal input from the user.
SIGCONT - This signal is generated when a suspended
process is resumed.
SIGPOLL - On SVR4 systems, this signal notifies the
process of an asynchronous I/O event. Note
that under 4.3+BSD, SIGIO and SIGPOLL are
the same. On other systems, SIGIO is ignored
by default, so gl_get_line() doesn't
trap it by default.
SIGPWR - This signal is generated when a power failure
occurs (presumably when the system is on a
UPS).
SIGALRM - This signal is generated when a timer
expires.
SIGUSR1 - An application specific signal.
SIGUSR2 - Another application specific signal.
SIGVTALRM - This signal is generated when a virtual
timer expires (see man setitimer(2)).
SIGXCPU - This signal is generated when a process
exceeds its soft CPU time limit.
SIGXFSZ - This signal is generated when a process
exceeds its soft file-size limit.
SIGTSTP - This signal is generated by the terminal
suspend key, which is usually ^Z, or the
delayed terminal suspend key, which is
usually ^Y.
SIGTTIN - This signal is generated if the program
attempts to read from the terminal while the
program is running in the background.
SIGTTOU - This signal is generated if the program
attempts to write to the terminal while the
program is running in the background.
Obviously not all of the above signals are supported on all systems, so code to support them is
conditionally compiled into the tecla library.
Note that if SIGKILL or SIGPOLL, which by definition can't be caught, or any of the hardware generated
exception signals, such as SIGSEGV, SIGBUS and SIGFPE, are received and unhandled while gl_get_line() has
the terminal in raw mode, the program will be terminated without the terminal having been restored to a
usable state. In practice, job-control shells usually reset the terminal settings when a process
relinquishes the controlling terminal, so this is only a problem with older shells.
CUSTOMIZED SIGNAL HANDLING
The previous section listed the signals that gl_get_line() traps by default, and described how it
responds to them. This section describes how to both add and remove signals from the list of trapped
signals, and how to specify how gl_get_line() should respond to a given signal.
If you don't need gl_get_line() to do anything in response to a signal that it normally traps, you can
tell to gl_get_line() to ignore that signal by calling gl_ignore_signal().
int gl_ignore_signal(GetLine *gl, int signo);
The signo argument is the number of the signal (eg. SIGINT) that you want to have ignored. If the
specified signal isn't currently one of those being trapped, this function does nothing.
The gl_trap_signal() function allows you to either add a new signal to the list that gl_get_line() traps,
or modify how it responds to a signal that it already traps.
int gl_trap_signal(GetLine *gl, int signo, unsigned flags,
GlAfterSignal after, int errno_value);
The signo argument is the number of the signal that you wish to have trapped. The flags argument is a set
of flags which determine the environment in which the application's signal handler is invoked, the after
argument tells gl_get_line() what to do after the application's signal handler returns, and errno_value
tells gl_get_line() what to set errno to if told to abort.
The flags argument is a bitwise OR of zero or more of the following enumerators:
GLS_RESTORE_SIG - Restore the caller's signal
environment while handling the
signal.
GLS_RESTORE_TTY - Restore the caller's terminal settings
while handling the signal.
GLS_RESTORE_LINE - Move the cursor to the start of the
line following the input line before
invoking the application's signal
handler.
GLS_REDRAW_LINE - Redraw the input line when the
application's signal handler returns.
GLS_UNBLOCK_SIG - Normally, if the calling program has
a signal blocked (man sigprocmask),
gl_get_line() does not trap that
signal. This flag tells gl_get_line()
to trap the signal and unblock it for
the duration of the call to
gl_get_line().
GLS_DONT_FORWARD - If this flag is included, the signal
will not be forwarded to the signal
handler of the calling program.
Two commonly useful flag combinations are also enumerated as follows:
GLS_RESTORE_ENV = GLS_RESTORE_SIG | GLS_RESTORE_TTY |
GLS_REDRAW_LINE
GLS_SUSPEND_INPUT = GLS_RESTORE_ENV | GLS_RESTORE_LINE
If your signal handler, or the default system signal handler for this signal, if you haven't overridden
it, never either writes to the terminal, nor suspends or terminates the calling program, then you can
safely set the flags argument to 0.
If your signal handler always writes to the terminal, reads from it, or suspends or terminates the
program, you should specify the flags argument as GL_SUSPEND_INPUT, so that:
1. The cursor doesn't get left in the middle of the input
line.
2. So that the user can type in input and have it echoed.
3. So that you don't need to end each output line with
\r\n, instead of just \n.
The GL_RESTORE_ENV combination is the same as GL_SUSPEND_INPUT, except that it doesn't move the cursor,
and if your signal handler doesn't read or write anything to the terminal, the user won't see any visible
indication that a signal was caught. This can be useful if you have a signal handler that only
occasionally writes to the terminal, where using GL_SUSPEND_LINE would cause the input line to be
unnecessarily duplicated when nothing had been written to the terminal. Such a signal handler, when it
does write to the terminal, should be sure to start a new line at the start of its first write, by
writing a \n character, and should be sure to leave the cursor on a new line before returning. If the
signal arrives while the user is entering a line that only occupies a signal terminal line, or if the
cursor is on the last terminal line of a longer input line, this will have the same effect as
GL_SUSPEND_INPUT. Otherwise it will start writing on a line that already contains part of the displayed
input line. This doesn't do any harm, but it looks a bit ugly, which is why the GL_SUSPEND_INPUT
combination is better if you know that you are always going to be writing to the terminal.
The after argument, which determines what gl_get_line() does after the application's signal handler
returns (if it returns), can take any one of the following values:
GLS_RETURN - Return the completed input line, just as
though the user had pressed the return
key.
GLS_ABORT - Cause gl_get_line() to abort. When
this happens, gl_get_line() returns
NULL, and a following call to
gl_return_status() will return
GLR_SIGNAL. Note that if the
application needs errno always to
have a meaningful value when
gl_get_line() returns NULL,
the callback function should set
errno appropriately.
GLS_CONTINUE - Resume command line editing.
The errno_value argument is intended to be combined with the GLS_ABORT option, telling gl_get_line() what
to set the standard errno variable to before returning NULL to the calling program. It can also, however,
be used with the GL_RETURN option, in case you wish to have a way to distinguish between an input line
that was entered using the return key, and one that was entered by the receipt of a signal.
RELIABLE SIGNAL HANDLING
Signal handling is suprisingly hard to do reliably without race conditions. In gl_get_line() a lot of
care has been taken to allow applications to perform reliable signal handling around gl_get_line(). This
section explains how to make use of this.
As an example of the problems that can arise if the application isn't written correctly, imagine that
one's application has a SIGINT signal handler that sets a global flag. Now suppose that the application
tests this flag just before invoking gl_get_line(). If a SIGINT signal happens to be received in the
small window of time between the statement that tests the value of this flag, and the statement that
calls gl_get_line(), then gl_get_line() will not see the signal, and will not be interrupted. As a
result, the application won't be able to respond to the signal until the user gets around to finishing
entering the input line and gl_get_line() returns. Depending on the application, this might or might not
be a disaster, but at the very least it would puzzle the user.
The way to avoid such problems is to do the following.
1. If needed, use the gl_trap_signal() function to
configure gl_get_line() to abort when important
signals are caught.
2. Configure gl_get_line() such that if any of the
signals that it catches are blocked when
gl_get_line() is called, they will be unblocked
automatically during times when gl_get_line() is
waiting for I/O. This can be done either
on a per signal basis, by calling the
gl_trap_signal() function, and specifying the
GLS_UNBLOCK attribute of the signal, or globally by
calling the gl_catch_blocked() function.
void gl_catch_blocked(GetLine *gl);
This function simply adds the GLS_UNBLOCK attribute
to all of the signals that it is currently configured to
trap.
3. Just before calling gl_get_line(), block delivery
of all of the signals that gl_get_line() is
configured to trap. This can be done using the POSIX
sigprocmask() function in conjunction with the
gl_list_signals() function.
int gl_list_signals(GetLine *gl, sigset_t *set);
This function returns the set of signals that it is
currently configured to catch in the set argument,
which is in the form required by sigprocmask().
4. In the example, one would now test the global flag that
the signal handler sets, knowing that there is now no
danger of this flag being set again until
gl_get_line() unblocks its signals while performing
I/O.
5. Eventually gl_get_line() returns, either because
a signal was caught, an error occurred, or the user
finished entering their input line.
6. Now one would check the global signal flag again, and if
it is set, respond to it, and zero the flag.
7. Use sigprocmask() to unblock the signals that were
blocked in step 3.
The same technique can be used around certain POSIX signal-aware functions, such as sigsetjmp() and
sigsuspend(), and in particular, the former of these two functions can be used in conjunction with
siglongjmp() to implement race-condition free signal handling around other long-running system calls. The
way to do this, is explained next, by showing how gl_get_line() manages to reliably trap signals around
calls to functions like read() and select() without race conditions.
The first thing that gl_get_line() does, whenever it is called, is to use the POSIX sigprocmask()
function to block the delivery of all of the signals that it is currently configured to catch. This is
redundant if the application has already blocked them, but it does no harm. It undoes this step just
before returning.
Whenever gl_get_line() needs to call read() or select() to wait for input from the user, it first calls
the POSIX sigsetjmp() function, being sure to specify a non-zero value for its savesigs argument. The
reason for the latter argument will become clear shortly.
If sigsetjmp() returns zero, gl_get_line() then does the following.
a. It uses the POSIX sigaction() function to register
a temporary signal handler to all of the signals that it
is configured to catch. This signal handler does two
things.
1. It records the number of the signal that was received
in a file-scope variable.
2. It then calls the POSIX siglongjmp()
function using the buffer that was passed to
sigsetjmp() for its first argument, and
a non-zero value for its second argument.
When this signal handler is registered, the sa_mask
member of the struct sigaction act argument of the
call to sigaction() is configured to contain all of
the signals that gl_get_line() is catching. This
ensures that only one signal will be caught at once by
our signal handler, which in turn ensures that multiple
instances of our signal handler don't tread on each
other's toes.
b. Now that the signal handler has been set up,
gl_get_line() unblocks all of the signals that it
is configured to catch.
c. It then calls the read() or select() system
calls to wait for keyboard input.
d. If this system call returns (ie. no signal is received),
gl_get_line() blocks delivery of the signals of
interest again.
e. It then reinstates the signal handlers that were
displaced by the one that was just installed.
Alternatively, if sigsetjmp() returns non-zero, this means that one of the signals being trapped was
caught while the above steps were executing. When this happens, gl_get_line() does the following.
First, note that when a call to siglongjmp() causes sigsetjmp() to return, provided that the savesigs
argument of sigsetjmp() was non-zero, as specified above, the signal process mask is restored to how it
was when sigsetjmp() was called. This is the important difference between sigsetjmp() and the older
problematic setjmp(), and is the essential ingredient that makes it possible to avoid signal handling
race conditions. Because of this we are guaranteed that all of the signals that we blocked before
calling sigsetjmp() are blocked again as soon as any signal is caught. The following statements, which
are then executed, are thus guaranteed to be executed without any further signals being caught.
1. If so instructed by the gl_get_line() configuration
attributes of the signal that was caught,
gl_get_line() restores the terminal attributes to
the state that they had when gl_get_line() was
called. This is particularly important for signals that
suspend or terminate the process, since otherwise the
terminal would be left in an unusable state.
2. It then reinstates the application's signal handlers.
3. Then it uses the C standard-library raise()
function to re-send the application the signal that
was caught.
3. Next it unblocks delivery of the signal that we just
sent. This results in the signal that was just sent
via raise(), being caught by the application's
original signal handler, which can now handle it as it
sees fit.
4. If the signal handler returns (ie. it doesn't terminate
the process), gl_get_line() blocks delivery of the
above signal again.
5. It then undoes any actions performed in the first of the
above steps, and redisplays the line, if the signal
configuration calls for this.
6. gl_get_line() then either resumes trying to
read a character, or aborts, depending on the
configuration of the signal that was caught.
What the above steps do in essence is to take asynchronously delivered signals and handle them
synchronously, one at a time, at a point in the code where gl_get_line() has complete control over its
environment.
THE TERMINAL SIZE
On most systems the combination of the TIOCGWINSZ ioctl and the SIGWINCH signal is used to maintain an
accurate idea of the terminal size. The terminal size is newly queried every time that gl_get_line() is
called and whenever a SIGWINCH signal is received.
On the few systems where this mechanism isn't available, at startup new_GetLine() first looks for the
LINES and COLUMNS environment variables. If these aren't found, or they contain unusable values, then if
a terminal information database like terminfo or termcap is available, the default size of the terminal
is looked up in this database. If this too fails to provide the terminal size, a default size of 80
columns by 24 lines is used.
Even on systems that do support ioctl(TIOCGWINSZ), if the terminal is on the other end of a serial line,
the terminal driver generally has no way of detecting when a resize occurs or of querying what the
current size is. In such cases no SIGWINCH is sent to the process, and the dimensions returned by
ioctl(TIOCGWINSZ) aren't correct. The only way to handle such instances is to provide a way for the user
to enter a command that tells the remote system what the new size is. This command would then call the
gl_set_term_size() function to tell gl_get_line() about the change in size.
int gl_set_term_size(GetLine *gl, int ncolumn, int nline);
The ncolumn and nline arguments are used to specify the new dimensions of the terminal, and must not be
less than 1. On systems that do support ioctl(TIOCGWINSZ), this function first calls ioctl(TIOCSWINSZ) to
tell the terminal driver about the change in size. In non-blocking server-I/O mode, if a line is
currently being input, the input line is then redrawn to accommodate the changed size. Finally the new
values are recorded in gl for future use by gl_get_line().
The gl_terminal_size() function allows you to query the current size of the terminal, and install an
alternate fallback size for cases where the size isn't available. Beware that the terminal size won't be
available if reading from a pipe or a file, so the default values can be important even on systems that
do support ways of finding out the terminal size.
typedef struct {
int nline; /* The terminal has nline lines */
int ncolumn; /* The terminal has ncolumn columns */
} GlTerminalSize;
GlTerminalSize gl_terminal_size(GetLine *gl,
int def_ncolumn,
int def_nline);
This function first updates gl_get_line()'s fallback terminal dimensions, then records its findings in
the return value.
The def_ncolumn and def_nline specify the default number of terminal columns and lines to use if the
terminal size can't be determined via ioctl(TIOCGWINSZ) or environment variables.
HIDING WHAT YOU TYPE
When entering sensitive information, such as passwords, it is best not to have the text that you are
entering echoed on the terminal. Furthermore, such text should not be recorded in the history list,
since somebody finding your terminal unattended could then recall it, or somebody snooping through your
directories could see it in your history file. With this in mind, the gl_echo_mode() function allows you
to toggle on and off the display and archival of any text that is subsequently entered in calls to
gl_get_line().
int gl_echo_mode(GetLine *gl, int enable);
The enable argument specifies whether entered text should be visible or not. If it is 0, then
subsequently entered lines will not be visible on the terminal, and will not be recorded in the history
list. If it is 1, then subsequent input lines will be displayed as they are entered, and provided that
history hasn't been turned off via a call to gl_toggle_history(), then they will also be archived in the
history list. Finally, if the enable argument is -1, then the echoing mode is left unchanged, which
allows you to non-destructively query the current setting via the return value. In all cases, the return
value of the function is 0 if echoing was disabled before the function was called, and 1 if it was
enabled.
When echoing is turned off, note that although tab completion will invisibly complete your prefix as far
as possible, ambiguous completions will not be displayed.
SINGLE CHARACTER QUERIES
Using gl_get_line() to query the user for a single character reply, is inconvenient for the user, since
they must hit the enter or return key before the character that they typed is returned to the program.
Thus the gl_query_char() function has been provided for single character queries like this.
int gl_query_char(GetLine *gl, const char *prompt,
char defchar);
This function displays the specified prompt at the start of a new line, and waits for the user to type a
character. When the user types a character, gl_query_char() displays it to the right of the prompt,
starts a newline, then returns the character to the calling program. The return value of the function is
the character that was typed. If the read had to be aborted for some reason, EOF is returned instead. In
the latter case, the application can call the previously documented gl_return_status(), to find out what
went wrong. This could, for example, have been the reception of a signal, or the optional inactivity
timer going off.
If the user simply hits enter, the value of the defchar argument is substituted. This means that when the
user hits either newline or return, the character specified in defchar, is displayed after the prompt, as
though the user had typed it, as well as being returned to the calling application. If such a replacement
is not important, simply pass '0 as the value of defchar.
If the entered character is an unprintable character, it is displayed symbolically. For example, control-
A is displayed as ^A, and characters beyond 127 are displayed in octal, preceded by a backslash.
As with gl_get_line(), echoing of the entered character can be disabled using the gl_echo_mode()
function.
If the calling process is suspended while waiting for the user to type their response, the cursor is
moved to the line following the prompt line, then when the process resumes, the prompt is redisplayed,
and gl_query_char() resumes waiting for the user to type a character.
Note that in non-blocking server mode, (see gl_io_mode(3)), if an incomplete input line is in the process
of being read when gl_query_char() is called, the partial input line is discarded, and erased from the
terminal, before the new prompt is displayed. The next call to gl_get_line() will thus start editing a
new line.
READING RAW CHARACTERS
Whereas the gl_query_char() function visibly prompts the user for a character, and displays what they
typed, the gl_read_char() function reads a signal character from the user, without writing anything to
the terminal, or perturbing any incompletely entered input line. This means that it can be called not
only from between calls to gl_get_line(), but also from callback functions that the application has
registered to be called by gl_get_line().
int gl_read_char(GetLine *gl);
On success, the return value of gl_read_char() is the character that was read. On failure, EOF is
returned, and the gl_return_status() function can be called to find out what went wrong. Possibilities
include the optional inactivity timer going off, the receipt of a signal that is configured to abort
gl_get_line(), or terminal I/O blocking, when in non-blocking server-I/O mode.
Beware that certain keyboard keys, such as function keys, and cursor keys, usually generate at least 3
characters each, so a single call to gl_read_char() won't be enough to identify such keystrokes.
CLEARING THE TERMINAL
The calling program can clear the terminal by calling gl_erase_terminal(). In non-blocking server-I/O
mode, this function also arranges for the current input line to be redrawn from scratch when
gl_get_line() is next called.
int gl_erase_terminal(GetLine *gl);
DISPLAYING TEXT DYNAMICALLY
Between calls to gl_get_line(), the gl_display_text() function provides a convenient way to display
paragraphs of text, left-justified and split over one or more terminal lines according to the constraints
of the current width of the terminal. Examples of the use of this function may be found in the demo
programs, where it is used to display introductions. In those examples the advanced use of optional
prefixes, suffixes and filled lines to draw a box around the text is also illustrated.
int gl_display_text(GetLine *gl, int indentation,
const char *prefix,
const char *suffix, int fill_char,
int def_width, int start,
const char *string);
If gl isn't currently connected to a terminal, for example if the output of a program that uses
gl_get_line() is being piped to another program or redirected to a file, then the value of the def_width
parameter is used as the terminal width.
The indentation argument specifies the number of characters to use to indent each line of output. The
fill_char argument specifies the character that will be used to perform this indentation.
The prefix argument can either be NULL, or be a string to place at the beginning of each new line (after
any indentation). Similarly, the suffix argument can either be NULL, or be a string to place at the end
of each line. The suffix is placed flush against the right edge of the terminal, and any space between
its first character and the last word on that line is filled with the character specified via the
fill_char argument. Normally the fill-character is a space.
The start argument tells gl_display_text() how many characters have already been written to the current
terminal line, and thus tells it the starting column index of the cursor. Since the return value of
gl_display_text() is the ending column index of the cursor, by passing the return value of one call to
the start argument of the next call, a paragraph that is broken between more than one string can be
composed by calling gl_display_text() for each successive portion of the paragraph. Note that literal
newline characters are necessary at the end of each paragraph to force a new line to be started.
On error, gl_display_text() returns -1.
CALLBACK FUNCTION FACILITIES
Unless otherwise stated, callback functions, such as tab completion callbacks and event callbacks should
not call any functions in this module. The following functions, however, are designed specifically to be
used by callback functions.
Calling the gl_replace_prompt() function from a callback tells gl_get_line() to display a different
prompt when the callback returns. Except in non-blocking server mode, it has no effect if used between
calls to gl_get_line(). In non-blocking server mode (see the gl_io_mode(3) man page, when used between
two calls to gl_get_line() that are operating on the same input line, the current input line will be re-
drawn with the new prompt on the following call to gl_get_line().
void gl_replace_prompt(GetLine *gl, const char *prompt);
INTERNATIONAL CHARACTER SETS
Since libtecla version 1.4.0, gl_get_line() has been 8-bit clean. This means that all 8-bit characters
that are printable in the user's current locale are now displayed verbatim and included in the returned
input line. Assuming that the calling program correctly contains a call like the following,
setlocale(LC_CTYPE, "");
then the current locale is determined by the first of the environment variables LC_CTYPE, LC_ALL, and
LANG, that is found to contain a valid locale name. If none of these variables are defined, or the
program neglects to call setlocale, then the default C locale is used, which is US 7-bit ASCII. On most
unix-like platforms, you can get a list of valid locales by typing the command:
locale -a
at the shell prompt. Further documentation on how the user can make use of this to enter international
characters can be found in the tecla(7) man page.
THREAD SAFETY
In a multi-threaded program, you should use the libtecla_r.a version of the library. This uses reentrant
versions of system functions, where available. Unfortunately neither terminfo nor termcap were designed
to be reentrant, so you can't safely use the functions of the getline module in multiple threads (you can
use the separate file-expansion and word-completion modules in multiple threads, see the corresponding
man pages for details). However due to the use of POSIX reentrant functions for looking up home
directories etc, it is safe to use this module from a single thread of a multi-threaded program, provided
that your other threads don't use any termcap or terminfo functions.
FILES
libtecla.a - The tecla library
libtecla.h - The tecla header file.
~/.teclarc - The personal tecla customization file.
SEE ALSO
libtecla(3), gl_io_mode(3), tecla(7), ef_expand_file(3),
cpl_complete_word(3), pca_lookup_file(3)
AUTHOR
Martin Shepherd (mcs@astro.caltech.edu)
gl_get_line(3)