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All Rights Reserved. .TH GL_GET_LINE 3TECLA "Sep 10, 2013" .SH NAME gl_get_line, new_GetLine, del_GetLine, gl_customize_completion, gl_change_terminal, gl_configure_getline, gl_load_history, gl_save_history, gl_group_history, gl_show_history, gl_watch_fd, gl_inactivity_timeout, gl_terminal_size, gl_set_term_size, gl_resize_history, gl_limit_history, gl_clear_history, gl_toggle_history, gl_lookup_history, gl_state_of_history, gl_range_of_history, gl_size_of_history, gl_echo_mode, gl_replace_prompt, gl_prompt_style, gl_ignore_signal, gl_trap_signal, gl_last_signal, gl_completion_action, gl_register_action, gl_display_text, gl_return_status, gl_error_message, gl_catch_blocked, gl_list_signals, gl_bind_keyseq, gl_erase_terminal, gl_automatic_history, gl_append_history, gl_query_char, gl_read_char \- allow the user to compose an input line .SH SYNOPSIS .LP .nf cc [ \fIflag\fR\&.\|.\|. ] \fIfile\fR\&.\|.\|. \fB-ltecla\fR [ \fIlibrary\fR\&.\|.\|. ] #include #include \fBGetLine *\fR\fBnew_GetLine\fR(\fBsize_t\fR \fIlinelen\fR, \fBsize_t\fR \fIhistlen\fR); .fi .LP .nf \fBGetLine *\fR\fBdel_GetLine\fR(\fBGetLine *\fR\fIgl\fR); .fi .LP .nf \fBchar *\fR\fBgl_get_line\fR(\fBGetLine *\fR\fIgl\fR, \fBconst char *\fR\fIprompt\fR, \fBconst char *\fR\fIstart_line\fR, \fBint\fR \fIstart_pos\fR); .fi .LP .nf \fBint\fR \fBgl_query_char\fR(\fBGetLine *\fR\fIgl\fR, \fBconst char *\fR\fIprompt\fR, \fBchar\fR \fIdefchar\fR); .fi .LP .nf \fBint\fR \fBgl_read_char\fR(\fBGetLine *\fR\fIgl\fR); .fi .LP .nf \fBint\fR \fBgl_customize_completion\fR(\fBGetLine *\fR\fIgl\fR, \fBvoid *\fR\fIdata\fR, \fBCplMatchFn *\fR\fImatch_fn\fR); .fi .LP .nf \fBint\fR \fBgl_change_terminal\fR(\fBGetLine *\fR\fIgl\fR, \fBFILE *\fR\fIinput_fp\fR, \fBFILE *\fR\fIoutput_fp\fR, \fBconst char *\fR\fIterm\fR); .fi .LP .nf \fBint\fR \fBgl_configure_getline\fR(\fBGetLine *\fR\fIgl\fR, \fBconst char *\fR\fIapp_string\fR, \fBconst char *\fR\fIapp_file\fR,\ \fBconst char *\fR\fIuser_file\fR); .fi .LP .nf \fBint\fR \fBgl_bind_keyseq\fR(\fBGetLine *\fR\fIgl\fR, \fBGlKeyOrigin\fR \fIorigin\fR, \fBconst char *\fR\fIkeyseq\fR, \fBconst char *\fR\fIaction\fR); .fi .LP .nf \fBint\fR \fBgl_save_history\fR(\fBGetLine *\fR\fIgl\fR, \fBconst char *\fR\fIfilename\fR, \fBconst char *\fR\fIcomment\fR, \fBint\fR \fImax_lines\fR); .fi .LP .nf \fBint\fR \fBgl_load_history\fR(\fBGetLine *\fR\fIgl\fR, \fBconst char *\fR\fIfilename\fR, \fBconst char *\fR\fIcomment\fR); .fi .LP .nf \fBint\fR \fBgl_watch_fd\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIfd\fR, \fBGlFdEvent\fR \fIevent\fR, \fBGlFdEventFn *\fR\fIcallback\fR, \fBvoid *\fR\fIdata\fR); .fi .LP .nf \fBint\fR \fBgl_inactivity_timeout\fR(\fBGetLine *\fR\fIgl\fR, \fBGlTimeoutFn *\fR\fIcallback\fR, \fBvoid *\fR\fIdata\fR, \fBunsigned long\fR \fIsec\fR, \fBunsigned long\fR \fInsec\fR); .fi .LP .nf \fBint\fR \fBgl_group_history\fR(\fBGetLine *\fR\fIgl\fR, \fBunsigned\fR \fIstream\fR); .fi .LP .nf \fBint\fR \fBgl_show_history\fR(\fBGetLine *\fR\fIgl\fR, \fBFILE *\fR\fIfp\fR, \fBconst char *\fR\fIfmt\fR, \fBint\fR \fIall_groups\fR, \fBint\fR \fImax_lines\fR); .fi .LP .nf \fBint\fR \fBgl_resize_history\fR(\fBGetLine *\fR\fIgl\fR, \fBsize_t\fR \fIbufsize\fR); .fi .LP .nf \fBvoid\fR \fBgl_limit_history\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fImax_lines\fR); .fi .LP .nf \fBvoid\fR \fBgl_clear_history\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIall_groups\fR); .fi .LP .nf \fBvoid\fR \fBgl_toggle_history\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIenable\fR); .fi .LP .nf \fBGlTerminalSize\fR \fBgl_terminal_size\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIdef_ncolumn\fR, \fBint\fR \fIdef_nline\fR); .fi .LP .nf \fBint\fR \fBgl_set_term_size\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIncolumn\fR, \fBint\fR \fInline\fR); .fi .LP .nf \fBint\fR \fBgl_lookup_history\fR(\fBGetLine *\fR\fIgl\fR, \fBunsigned long\fR \fIid\fR, \fBGlHistoryLine *\fR\fIhline\fR); .fi .LP .nf \fBvoid\fR \fBgl_state_of_history\fR(\fBGetLine *\fR\fIgl\fR, \fBGlHistoryState *\fR\fIstate\fR); .fi .LP .nf \fBvoid\fR \fBgl_range_of_history\fR(\fBGetLine *\fR\fIgl\fR, \fBGlHistoryRange *\fR\fIrange\fR); .fi .LP .nf \fBvoid\fR \fBgl_size_of_history\fR(\fBGetLine *\fR\fIgl\fR, \fBGlHistorySize *\fR\fIsize\fR); .fi .LP .nf \fBvoid\fR \fBgl_echo_mode\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIenable\fR); .fi .LP .nf \fBvoid\fR \fBgl_replace_prompt\fR(\fBGetLine *\fR\fIgl\fR, \fBconst char *\fR\fIprompt\fR); .fi .LP .nf \fBvoid\fR \fBgl_prompt_style\fR(\fBGetLine *\fR\fIgl\fR, \fBGlPromptStyle\fR \fIstyle\fR); .fi .LP .nf \fBint\fR \fBgl_ignore_signal\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIsigno\fR); .fi .LP .nf \fBint\fR \fBgl_trap_signal\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIsigno\fR, \fBunsigned\fR \fIflags\fR, \fBGlAfterSignal\fR \fIafter\fR, \fBint\fR \fIerrno_value\fR); .fi .LP .nf \fBint\fR \fBgl_last_signal\fR(\fBGetLine *\fR\fIgl\fR); .fi .LP .nf \fBint\fR \fBgl_completion_action\fR(\fBGetLine *\fR\fIgl\fR, \fBvoid *\fR\fIdata\fR, \fBCplMatchFn *\fR\fImatch_fn\fR, \fBint\fR \fIlist_only\fR, \fBconst char *\fR\fIname\fR, \fBconst char *\fR\fIkeyseq\fR); .fi .LP .nf \fBint\fR \fBgl_register_action\fR(\fBGetLine *\fR\fIgl\fR, \fBvoid *\fR\fIdata\fR, \fBGlActionFn *\fR\fIfn\fR, \fBconst char *\fR\fIname\fR, \fBconst char *\fR\fIkeyseq\fR); .fi .LP .nf \fBint\fR \fBgl_display_text\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIindentation\fR, \fBconst char *\fR\fIprefix\fR, \fBconst char *\fR\fIsuffix\fR, \fBint\fR \fIfill_char\fR, \fBint\fR \fIdef_width\fR, \fBint\fR \fIstart\fR, \fBconst char *\fR\fIstring\fR); .fi .LP .nf \fBGlReturnStatus\fR \fBgl_return_status\fR(\fBGetLine *\fR\fIgl\fR); .fi .LP .nf \fBconst char *\fR\fBgl_error_message\fR(\fBGetLine *\fR\fIgl\fR, \fBchar *\fR\fIbuff\fR, \fBsize_t\fR \fIn\fR); .fi .LP .nf \fBvoid\fR \fBgl_catch_blocked\fR(\fBGetLine *\fR\fIgl\fR); .fi .LP .nf \fBint\fR \fBgl_list_signals\fR(\fBGetLine *\fR\fIgl\fR, \fBsigset_t *\fR\fIset\fR); .fi .LP .nf \fBint\fR \fBgl_append_history\fR(\fBGetLine *\fR\fIgl\fR, \fBconst char *\fR\fIline\fR); .fi .LP .nf \fBint\fR \fBgl_automatic_history\fR(\fBGetLine *\fR\fIgl\fR, \fBint\fR \fIenable\fR); .fi .LP .nf \fBint\fR \fBgl_erase_terminal\fR(\fBGetLine *\fR\fIgl\fR); .fi .SH DESCRIPTION .sp .LP The \fBgl_get_line()\fR function is part of the \fBlibtecla\fR(3LIB) library. If the user is typing at a terminal, each call prompts them for an line of input, then provides interactive editing facilities, similar to those of the UNIX \fBtcsh\fR 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 on the \fBtecla\fR(5) manual page. .SS "An Example" .sp .LP The following shows a complete example of how to use the \fBgl_get_line()\fR function to get input from the user: .sp .in +2 .nf #include #include #include 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\en") != 0) printf("You typed: %s\en", line); gl = del_GetLine(gl); return 0; } .fi .in -2 .sp .LP In the example, first the resources needed by the \fBgl_get_line()\fR function are created by calling \fBnew_GetLine()\fR. This allocates the memory used in subsequent calls to the \fBgl_get_line()\fR 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 \fBnew_GetLine()\fR, are returned to the system by calling \fBdel_GetLine()\fR. Note the use of the \fINULL\fR return value of \fBdel_GetLine()\fR to make \fIgl\fR \fINULL\fR. This is a safety precaution. If the program subsequently attempts to pass \fIgl\fR to \fBgl_get_line()\fR, said function will complain, and return an error, instead of attempting to use the deleted resource object. .SS "The Functions Used In The Example" .sp .LP The \fBnew_GetLine()\fR function creates the resources used by the \fBgl_get_line()\fR function and returns an opaque pointer to the object that contains them. The maximum length of an input line is specified by the \fIlinelen\fR argument, and the number of bytes to allocate for storing history lines is set by the \fIhistlen\fR 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 description of the \fBgl_limit_history()\fR function. If you do not want history at all, specify \fIhistlen\fR as zero, and no history buffer will be allocated. .sp .LP On error, a message is printed to \fBstderr\fR and \fINULL\fR is returned. .sp .LP The \fBdel_GetLine()\fR function deletes the resources that were returned by a previous call to \fBnew_GetLine()\fR. It always returns \fINULL\fR (for example, a deleted object). It does nothing if the \fIgl\fR argument is \fINULL\fR. .sp .LP The \fBgl_get_line()\fR 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 \fBnew_GetLine()\fR. The \fIprompt\fR argument should be a normal null-terminated string, specifying the prompt to present the user with. By default prompts are displayed literally, but if enabled with the \fBgl_prompt_style()\fR function, prompts can contain directives to do underlining, switch to and from bold fonts, or turn highlighting on and off. .sp .LP If you want to specify the initial contents of the line for the user to edit, pass the desired string with the \fIstart_line\fR argument. You can then specify which character of this line the cursor is initially positioned over by using the \fIstart_pos\fR argument. This should be -1 if you want the cursor to follow the last character of the start line. If you do not want to preload the line in this manner, send \fIstart_line\fR as \fINULL\fR, and set \fIstart_pos\fR to -1. .sp .LP The \fBgl_get_line()\fR function returns a pointer to the line entered by the user, or \fINULL\fR on error or at the end of the input. The returned pointer is part of the specified \fIgl\fR resource object, and thus should not be freed by the caller, or assumed to be unchanging from one call to the next. When reading from a user at a terminal, there will always be a newline character at the end of the returned line. When standard input is being taken from a pipe or a file, there will similarly be a newline unless the input line was too long to store in the internal buffer. In the latter case you should call \fBgl_get_line()\fR again to read the rest of the line. Note that this behavior makes \fBgl_get_line()\fR similar to \fBfgets\fR(3C). When \fBstdin\fR is not connected to a terminal, \fBgl_get_line()\fR simply calls \fBfgets()\fR. .SS "The Return Status Of \fBgl_get_line()\fR" .sp .LP The \fBgl_get_line()\fR function has two possible return values: a pointer to the completed input line, or \fINULL\fR. Additional information about what caused \fBgl_get_line()\fR to return is available both by inspecting \fBerrno\fR and by calling the \fBgl_return_status()\fR function. .sp .LP The following are the possible enumerated values returned by \fBgl_return_status()\fR: .sp .ne 2 .na \fB\fBGLR_NEWLINE\fR\fR .ad .RS 15n The last call to \fBgl_get_line()\fR successfully returned a completed input line. .RE .sp .ne 2 .na \fB\fBGLR_BLOCKED\fR\fR .ad .RS 15n The \fBgl_get_line()\fR function was in non-blocking server mode, and returned early to avoid blocking the process while waiting for terminal I/O. The \fBgl_pending_io()\fR function can be used to see what type of I/O \fBgl_get_line()\fR was waiting for. See the \fBgl_io_mode\fR(3TECLA). .RE .sp .ne 2 .na \fB\fBGLR_SIGNAL\fR\fR .ad .RS 15n A signal was caught by \fBgl_get_line()\fR that had an after-signal disposition of \fBGLS_ABORT\fR. See \fBgl_trap_signal()\fR. .RE .sp .ne 2 .na \fB\fBGLR_TIMEOUT\fR\fR .ad .RS 15n The inactivity timer expired while \fBgl_get_line()\fR was waiting for input, and the timeout callback function returned \fBGLTO_ABORT\fR. See \fBgl_inactivity_timeout()\fR for information about timeouts. .RE .sp .ne 2 .na \fB\fBGLR_FDABORT\fR\fR .ad .RS 15n An application I/O callback returned \fBGLFD_ABORT\fR. Ssee \fBgl_watch_fd()\fR. .RE .sp .ne 2 .na \fB\fBGLR_EOF\fR\fR .ad .RS 15n 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. .RE .sp .ne 2 .na \fB\fBGLR_ERROR\fR\fR .ad .RS 15n An unexpected error caused \fBgl_get_line()\fR to abort (consult \fBerrno\fR and/or \fBgl_error_message()\fR for details. .RE .sp .LP When \fBgl_return_status()\fR returns \fBGLR_ERROR\fR and the value of \fBerrno\fR is not sufficient to explain what happened, you can use the \fBgl_error_message()\fR function to request a description of the last error that occurred. .sp .LP The return value of \fBgl_error_message()\fR is a pointer to the message that occurred. If the \fIbuff\fR argument is \fINULL\fR, this will be a pointer to a buffer within \fIgl\fR whose value will probably change on the next call to any function associated with \fBgl_get_line()\fR. Otherwise, if a non-null \fIbuff\fR argument is provided, the error message, including a '\e0' terminator, will be written within the first \fIn\fR elements of this buffer, and the return value will be a pointer to the first element of this buffer. If the message will not fit in the provided buffer, it will be truncated to fit. .SS "Optional Prompt Formatting" .sp .LP Whereas by default the prompt string that you specify is displayed literally without any special interpretation of the characters within it, the \fBgl_prompt_style()\fR function can be used to enable optional formatting directives within the prompt. .sp .LP The \fIstyle\fR argument, which specifies the formatting style, can take any of the following values: .sp .ne 2 .na \fB\fBGL_FORMAT_PROMPT\fR\fR .ad .RS 21n In this style, the formatting directives described below, when included in prompt strings, are interpreted as follows: .sp .ne 2 .na \fB\fB%B\fR\fR .ad .RS 6n Display subsequent characters with a bold font. .RE .sp .ne 2 .na \fB\fB%b\fR\fR .ad .RS 6n Stop displaying characters with the bold font. .RE .sp .ne 2 .na \fB\fB%F\fR\fR .ad .RS 6n Make subsequent characters flash. .RE .sp .ne 2 .na \fB\fB%f\fR\fR .ad .RS 6n Turn off flashing characters. .RE .sp .ne 2 .na \fB\fB%U\fR\fR .ad .RS 6n Underline subsequent characters. .RE .sp .ne 2 .na \fB\fB%u\fR\fR .ad .RS 6n Stop underlining characters. .RE .sp .ne 2 .na \fB\fB%P\fR\fR .ad .RS 6n Switch to a pale (half brightness) font. .RE .sp .ne 2 .na \fB\fB%p\fR\fR .ad .RS 6n Stop using the pale font. .RE .sp .ne 2 .na \fB\fB%S\fR\fR .ad .RS 6n Highlight subsequent characters (also known as standout mode). .RE .sp .ne 2 .na \fB\fB%s\fR\fR .ad .RS 6n Stop highlighting characters. .RE .sp .ne 2 .na \fB\fB%V\fR\fR .ad .RS 6n Turn on reverse video. .RE .sp .ne 2 .na \fB\fB%v\fR\fR .ad .RS 6n Turn off reverse video. .RE .sp .ne 2 .na \fB\fB%%\fR\fR .ad .RS 6n Display a single % character. .RE For example, in this mode, a prompt string like "%UOK%u$" would display the prompt "OK$", but with the OK part underlined. .sp Note that although a pair of characters that starts with a % character, but does not match any of the above directives is displayed literally, if a new directive is subsequently introduced which does match, the displayed prompt will change, so it is better to always use %% to display a literal %. .sp Also note that not all terminals support all of these text attributes, and that some substitute a different attribute for missing ones. .RE .sp .ne 2 .na \fB\fBGL_LITERAL_PROMPT\fR\fR .ad .RS 21n In this style, the prompt string is printed literally. This is the default style. .RE .SS "Alternate Configuration Sources" .sp .LP By default users have the option of configuring the behavior of \fBgl_get_line()\fR with a configuration file called \fB\&.teclarc\fR 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 \fBgl_configure_getline()\fR function allows the application to control where configuration information is read from. .sp .LP The \fBgl_configure_getline()\fR function allows the configuration commands that would normally be read from a user's \fB~/.teclarc\fR 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 \fBgl_get_line()\fR, the default behavior of reading \fB~/.teclarc\fR on the first call to \fBgl_get_line()\fR is disabled, so all configurations must be achieved using the configuration sources specified with this function. .sp .LP If \fIapp_string\fR != \fINULL\fR, 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 \fIapp_file\fR != \fINULL\fR then it is interpreted as the full pathname of an application-specific configuration file. If user_file != \fINULL\fR then it is interpreted as the full path name of a user-specific configuration file, such as \fB~/.teclarc\fR. For example, in the call .sp .in +2 .nf gl_configure_getline(gl, "edit-mode vi \en nobeep", "/usr/share/myapp/teclarc", "~/.teclarc"); .fi .in -2 .sp .LP The \fIapp_string\fR argument causes the calling application to start in \fBvi\fR(1) edit-mode, instead of the default \fBemacs\fR 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 \fB/usr/share/myapp/teclarc\fR, then finally reads user-specific configuration commands from an optional \fB\&.teclarc\fR file in the user's home directory. Note that the arguments are listed in ascending order of priority, with the contents of \fIapp_string\fR being potentially over riden by commands in \fIapp_file\fR, and commands in \fIapp_file\fR potentially being overriden by commands in \fIuser_file\fR. .sp .LP You can call this function as many times as needed, the results being cumulative, but note that copies of any file names specified with the \fIapp_file\fR and \fIuser_file\fR 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. .sp .LP Individual key sequences can also be bound and unbound using the \fBgl_bind_keyseq()\fR function. The \fIorigin\fR argument specifies the priority of the binding, according to whom it is being established for, and must be one of the following two values. .sp .ne 2 .na \fB\fBGL_USER_KEY\fR\fR .ad .RS 15n The user requested this key-binding. .RE .sp .ne 2 .na \fB\fBGL_APP_KEY\fR\fR .ad .RS 15n This is a default binding set by the application. .RE .sp .LP When both user and application bindings for a given key sequence have been specified, the user binding takes precedence. The application's binding is subsequently reinstated if the user's binding is later unbound with either another call to this function, or a call to \fBgl_configure_getline()\fR. .sp .LP The \fIkeyseq\fR argument specifies the key sequence to be bound or unbound, and is expressed in the same way as in a \fB~/.teclarc\fR configuration file. The \fIaction\fR argument must either be a string containing the name of the action to bind the key sequence to, or it must be \fINULL\fR or \fB""\fR to unbind the key sequence. .SS "Customized Word Completion" .sp .LP If in your application you would like to have TAB completion complete other things in addition to or instead of filenames, you can arrange this by registering an alternate completion callback function with a call to the \fBgl_customize_completion()\fR function. .sp .LP The \fIdata\fR 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 \fImatch_fn\fR argument specifies the callback function to be called. The \fICplMatchFn\fR function type is defined in <\fBlibtecla.h\fR>, as is a \fBCPL_MATCH_FN()\fR macro that you can use to declare and prototype callback functions. The declaration and responsibilities of callback functions are described in depth on the \fBcpl_complete_word\fR(3TECLA) manual page. .sp .LP The callback function is responsible for looking backwards in the input line from the point at which the user pressed TAB, to find the start of the word being completed. It then must lookup possible completions of this word, and record them one by one in the \fBWordCompletion\fR object that is passed to it as an argument, by calling the \fBcpl_add_completion()\fR function. If the callback function wants to provide filename completion in addition to its own specific completions, it has the option of itself calling the builtin filename completion callback. This also is documented on the \fBcpl_complete_word\fR(3TECLA) manual page. .sp .LP If you would like \fBgl_get_line()\fR to return the current input line when a successful completion is been made, you can arrange this when you call \fBcpl_add_completion()\fR by making the last character of the continuation suffix a newline character. The input line will be updated to display the completion, together with any contiuation suffix up to the newline character, and \fBgl_get_line()\fR will return this input line. .sp .LP If your callback function needs to write something to the terminal, it must call \fBgl_normal_io()\fR before doing so. This will start a new line after the input line that is currently being edited, reinstate normal terminal I/O, and notify \fBgl_get_line()\fR that the input line will need to be redrawn when the callback returns. .SS "Adding Completion Actions" .sp .LP 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 \fBgl_completion_action()\fR function. .sp .LP The \fIdata\fR and \fImatch_fn\fR arguments are as described on the \fBcpl_complete_word\fR(3TECLA) manual page, and specify the callback function that should be invoked to identify possible completions. The \fIlist_only\fR 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 \fIname\fR 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 \fIkeyseq\fR argument specifies the default key sequence to bind the action to. If this is \fINULL\fR, no new key sequence will be bound to the action. .sp .LP Beware that in order for the user to be able to change the key sequence that is bound to actions that are installed in this manner, you shouldcall \fBgl_completion_action()\fR to install a given action for the first time between calling \fBnew_GetLine()\fR and the first call to \fBgl_get_line()\fR. Otherwise, when the user's configuration file is read on the first call to \fBgl_get_line()\fR, the name of the your additional action will not be known, and any reference to it in the configuration file will generate an error. .sp .LP As discussed for \fBgl_customize_completion()\fR, if your callback function needs to write anything to the terminal, it must call \fBgl_normal_io()\fR before doing so. .SS "Defining Custom Actions" .sp .LP 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 \fBgl_register_action()\fR function is provided. .sp .LP The \fBgl_register_action()\fR function lets the application register an external function, \fIfn\fR, that will thereafter be called whenever either the specified key sequence, \fIkeyseq\fR, is entered by the user, or the user enters any other key sequence that the user subsequently binds to the specified action name, \fIname\fR, in their configuration file. The \fIdata\fR argument can be a pointer to anything that the application wants to have passed to the action function, \fIfn\fR, whenever that function is invoked. .sp .LP The action function, \fIfn\fR, should be declared using the \fBGL_ACTION_FN()\fR macro, which is defined in <\fBlibtecla.h\fR>. .sp .in +2 .nf #define GL_ACTION_FN(fn) GlAfterAction (fn)(GetLine *gl, \e void *data, int count, size_t curpos, \e const char *line) .fi .in -2 .sp .LP The \fIgl\fR and \fIdata\fR arguments are those that were previously passed to \fBgl_register_action()\fR when the action function was registered. The \fIcount\fR 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 does not enter a number, then the \fIcount\fR 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 \fIcount\fR argument, or use its value for a different purpose. .sp .LP A copy of the current input line is passed in the read-only \fIline\fR argument. The current cursor position within this string is given by the index contained in the \fIcurpos\fR argument. Note that direct manipulation of the input line and the cursor position is not permitted because the rules dictated by various modes (such as \fBvi\fR mode versus \fBemacs\fR mode, no-echo mode, and insert mode versus overstrike mode) make it too complex for an application writer to write a conforming editing action, as well as constrain future changes to the internals of \fBgl_get_line()\fR. A potential solution to this dilemma would be to allow the action function to edit the line using the existing editing actions. This is currently under consideration. .sp .LP 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 \fBgl_normal_io()\fR 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 \fBstdio\fR facilities. The latter includes such things as restoring the normal mapping of \en to \er\en, 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 is not necessary for the action function to restore the original editing environment before it returns. This is done automatically by \fBgl_get_line()\fR after the action function returns. The following is a simple example of an action function which writes the sentence "Hello world" on a new terminal line after the line being edited. When this function returns, the input line is redrawn on the line that follows the "Hello world" line, and line editing resumes. .sp .in +2 .nf static GL_ACTION_FN(say_hello_fn) { if(gl_normal_io(gl)) /* Temporarily suspend editing */ return GLA_ABORT; printf("Hello world\en"); return GLA_CONTINUE; } .fi .in -2 .sp .LP Action functions must return one of the following values, to tell \fBgl_get_line()\fR how to proceed. .sp .ne 2 .na \fB\fBGLA_ABORT\fR\fR .ad .RS 16n Cause \fBgl_get_line()\fR to return \fINULL\fR. .RE .sp .ne 2 .na \fB\fBGLA_RETURN\fR\fR .ad .RS 16n Cause \fBgl_get_line()\fR to return the completed input line .RE .sp .ne 2 .na \fB\fBGLA_CONTINUE\fR\fR .ad .RS 16n Resume command-line editing. .RE .sp .LP Note that the \fIname\fR argument of \fBgl_register_action()\fR specifies the name by which a user can refer to the action in their configuration file. This allows them to re-bind the action to an alternate key-sequence. In order for this to work, it is necessary to call \fBgl_register_action()\fR between calling \fBnew_GetLine()\fR and the first call to \fBgl_get_line()\fR. .SS "History Files" .sp .LP To save the contents of the history buffer before quitting your application and subsequently restore them when you next start the application, the \fBgl_save_history()\fR and \fBgl_load_history()\fR functions are provided. .sp .LP The \fIfilename\fR 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 \fB~/.myapp_history\fR or \fB$HOME/.myapp_history\fR. .sp .LP Along with each history line, additional information about it, such as its nesting level and when it was entered by the user, is recorded as a comment preceding the line in the history file. Writing this as a 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 \fBgl_load_history()\fR that you used when you called \fBgl_save_history()\fR to write the history file. .sp .LP The \fImax_lines\fR argument must be either -1 to specify that all lines in the history list be saved, or a positive number specifying a ceiling on how many of the most recent lines should be saved. .sp .LP Both fuctions return non-zero on error, after writing an error message to \fBstderr\fR. Note that \fBgl_load_history()\fR does not consider the non-existence of a file to be an error. .SS "Multiple History Lists" .sp .LP If your application uses a single \fBGetLine\fR object for entering many different types of input lines, you might want \fBgl_get_line()\fR 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, \fBgl_get_line()\fR marks lines being recorded in the history list with an integer identifier chosen by the application. Initially this identifier is set to 0 by \fBnew_GetLine()\fR, but it can be changed subsequently by calling \fBgl_group_history()\fR. .sp .LP The integer identifier ID can be any number chosen by the application, but note that \fBgl_save_history()\fR and \fBgl_load_history()\fR preserve the association between identifiers and historical input lines between program invocations, so you should choose fixed identifiers for the different types of input line used by your application. .sp .LP Whenever \fBgl_get_line()\fR 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. .SS "Displaying History" .sp .LP The history list can be displayed by calling \fBgl_show_history()\fR. This function displays the current contents of the history list to the \fBstdio\fR output stream \fIfp\fR. If the \fImax_lines\fR argument is greater than or equal to zero, then no more than this number of the most recent lines will be displayed. If the \fIall_groups\fR argument is non-zero, lines from all history groups are displayed. Otherwise only those of the currently selected history group are displayed. The format string argument, \fIfmt\fR, determines how the line is displayed. This can contain arbitrary characters which are written verbatim, interleaved with any of the following format directives: .sp .ne 2 .na \fB\fB%D\fR\fR .ad .RS 6n The date on which the line was originally entered, formatted like 2001-11-20. .RE .sp .ne 2 .na \fB\fB%T\fR\fR .ad .RS 6n The time of day when the line was entered, formatted like 23:59:59. .RE .sp .ne 2 .na \fB\fB%N\fR\fR .ad .RS 6n The sequential entry number of the line in the history buffer. .RE .sp .ne 2 .na \fB\fB%G\fR\fR .ad .RS 6n The number of the history group which the line belongs to. .RE .sp .ne 2 .na \fB\fB%%\fR\fR .ad .RS 6n A literal % character. .RE .sp .ne 2 .na \fB\fB%H\fR\fR .ad .RS 6n The history line itself. .RE .sp .LP Thus a format string like "%D %T %H0" would output something like: .sp .in +2 .nf 2001-11-20 10:23:34 Hello world .fi .in -2 .sp .LP Note the inclusion of an explicit newline character in the format string. .SS "Looking Up History" .sp .LP The \fBgl_lookup_history()\fR function allows the calling application to look up lines in the history list. .sp .LP The \fIid\fR argument indicates which line to look up, where the first line that was entered in the history list after \fBnew_GetLine()\fR 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 \fBgl_range_of_history()\fR function. If the requested line is in the history list, the details of the line are recorded in the variable pointed to by the \fIhline\fR argument, and 1 is returned. Otherwise 0 is returned, and the variable pointed to by \fIhline\fR is left unchanged. .sp .LP Beware that the string returned in \fIhline\fR->\fIline\fR 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 \fIgl\fR as its argument. Therefore you should make a private copy of this string if you need to keep it. .SS "Manual History Archival" .sp .LP By default, whenever a line is entered by the user, it is automatically appended to the history list, just before \fBgl_get_line()\fR 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 \fBgl_automatic_history()\fR function. .sp .LP If this function is called with its \fIenable\fR argument set to 0, \fBgl_get_line()\fR will not automatically archive subsequently entered lines. Automatic archiving can be reenabled at a later time by calling this function again, with its \fIenable\fR argument set to 1. While automatic history archiving is disabled, the calling application can use the \fBgl_append_history()\fR to append lines to the history list as needed. .sp .LP The \fIline\fR argument specifies the line to be added to the history list. This must be a normal '\e0 ' 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 '\e0 ' terminator. If the line is longer than the maximum input line length that was specified when \fBnew_GetLine()\fR was called, it will be truncated to the actual \fBgl_get_line()\fR line length when the line is recalled. .sp .LP If successful, \fBgl_append_history()\fR returns 0. Otherwise it returns non-zero and sets \fBerrno\fR to one of the following values. .sp .ne 2 .na \fB\fBEINVAL\fR\fR .ad .RS 10n One of the arguments passed to \fBgl_append_history()\fR was \fINULL\fR. .RE .sp .ne 2 .na \fB\fBENOMEM\fR\fR .ad .RS 10n The specified line was longer than the allocated size of the history buffer (as specified when \fBnew_GetLine()\fR was called), so it could not be archived. .RE .sp .LP A textual description of the error can optionally be obtained by calling \fBgl_error_message()\fR. 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 \fBgl_append_history()\fR. .SS "Miscellaneous History Configuration" .sp .LP If you wish to change the size of the history buffer that was originally specified in the call to \fBnew_GetLine()\fR, you can do so with the \fBgl_resize_history()\fR function. .sp .LP The \fIhistlen\fR argument specifies the new size in bytes, and if you specify this as 0, the buffer will be deleted. .sp .LP As mentioned in the discussion of \fBnew_GetLine()\fR, the number of lines that can be stored in the history buffer, depends on the lengths of the individual lines. For example, a 1000 byte buffer could equally store 10 lines of average length 100 bytes, or 20 lines of average length 50 bytes. Although the buffer is never expanded when new lines are added, a list of pointers into the buffer does get expanded when needed to accomodate the number of lines currently stored in the buffer. To place an upper limit on the number of lines in the buffer, and thus a ceiling on the amount of memory used in this list, you can call the \fBgl_limit_history()\fR function. .sp .LP The \fImax_lines\fR 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 \fImax_lines\fR most recently appended lines are kept in the buffer. Older lines are discarded. .sp .LP To discard lines from the history buffer, use the \fBgl_clear_history()\fR function. .sp .LP The \fIall_groups\fR argument tells the function whether to delete just the lines associated with the current history group (see \fBgl_group_history()\fR) or all historical lines in the buffer. .sp .LP The \fBgl_toggle_history()\fR function allows you to toggle history on and off without losing the current contents of the history list. .sp .LP Setting the \fIenable\fR 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. .SS "Querying History Information" .sp .LP The configured state of the history list can be queried with the \fBgl_history_state()\fR function. On return, the status information is recorded in the variable pointed to by the \fIstate\fR argument. .sp .LP The \fBgl_range_of_history()\fR function returns the number and range of lines in the history list. The return values are recorded in the variable pointed to by the range argument. If the \fInlines\fR member of this structure is greater than zero, then the oldest and newest members report the range of lines in the list, and \fInewest\fR=\fIoldest\fR+\fInlines\fR-1. Otherwise they are both zero. .sp .LP The \fBgl_size_of_history()\fR function returns the total size of the history buffer and the amount of the buffer that is currently occupied. .sp .LP On return, the size information is recorded in the variable pointed to by the \fIsize\fR argument. .SS "Changing Terminals" .sp .LP The \fBnew_GetLine()\fR constructor function assumes that input is to be read from \fBstdin\fR and output written to \fBstdout\fR. The following function allows you to switch to different input and output streams. .sp .LP The \fIgl\fR argument is the object that was returned by \fBnew_GetLine()\fR. The \fIinput_fp\fR argument specifies the stream to read from, and \fIoutput_fp\fR specifies the stream to be written to. Only if both of these refer to a terminal, will interactive terminal input be enabled. Otherwise \fBgl_get_line()\fR will simply call \fBfgets()\fR to read command input. If both streams refer to a terminal, then they must refer to the same terminal, and the type of this terminal must be specified with the \fIterm\fR argument. The value of the \fIterm\fR argument is looked up in the terminal information database (\fBterminfo\fR or \fBtermcap\fR), in order to determine which special control sequences are needed to control various aspects of the terminal. \fBnew_GetLine()\fR for example, passes the return value of \fBgetenv\fR("TERM") in this argument. Note that if one or both of \fIinput_fp\fR and \fIoutput_fp\fR do not refer to a terminal, then it is legal to pass \fINULL\fR instead of a terminal type. .sp .LP Note that if you want to pass file descriptors to \fBgl_change_terminal()\fR, you can do this by creating \fBstdio\fR stream wrappers using the POSIX \fBfdopen\fR(3C) function. .SS "External Event Handling" .sp .LP By default, \fBgl_get_line()\fR does not return until either a complete input line has been entered by the user, or an error occurs. In programs that need to watch for I/O from other sources than the terminal, there are two options. .RS +4 .TP .ie t \(bu .el o Use the functions described in the \fBgl_io_mode\fR(3TECLA) manual page to switch \fBgl_get_line()\fR into non-blocking server mode. In this mode, \fBgl_get_line()\fR 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 \fBgl_get_line()\fR. .RE .RS +4 .TP .ie t \(bu .el o While \fBgl_get_line()\fR is waiting for keyboard input from the user, you can ask it to also watch for activity on arbitrary file descriptors, such as network sockets or pipes, and have it call functions of your choosing when activity is seen. This works on any system that has the select system call, which is most, if not all flavors of UNIX. .RE .sp .LP Registering a file descriptor to be watched by \fBgl_get_line()\fR involves calling the \fBgl_watch_fd()\fR function. If this returns non-zero, then it means that either your arguments are invalid, or that this facility is not supported on the host system. .sp .LP The \fIfd\fR 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: .sp .ne 2 .na \fB\fBGLFD_READ\fR\fR .ad .RS 15n Watch for the arrival of data to be read. .RE .sp .ne 2 .na \fB\fBGLFD_WRITE\fR\fR .ad .RS 15n Watch for the ability to write to the file descriptor without blocking. .RE .sp .ne 2 .na \fB\fBGLFD_URGENT\fR\fR .ad .RS 15n Watch for the arrival of urgent out-of-band data on the file descriptor. .RE .sp .LP The \fIcallback\fR argument is the function to call when the selected activity is seen. It should be defined with the following macro, which is defined in libtecla.h. .sp .in +2 .nf #define GL_FD_EVENT_FN(fn) GlFdStatus (fn)(GetLine *gl, \ void *data, int fd, GlFdEvent event) .fi .in -2 .sp .LP The data argument of the \fBgl_watch_fd()\fR function is passed to the callback function for its own use, and can point to anything you like, including \fINULL\fR. The file descriptor and the event argument are also passed to the callback function, and this potentially allows the same callback function to be registered to more than one type of event and/or more than one file descriptor. The return value of the callback function should be one of the following values. .sp .ne 2 .na \fB\fBGLFD_ABORT\fR\fR .ad .RS 17n Tell \fBgl_get_line()\fR to abort. When this happens, \fBgl_get_line()\fR returns \fINULL\fR, and a following call to \fBgl_return_status()\fR will return \fBGLR_FDABORT\fR. Note that if the application needs \fBerrno\fR always to have a meaningful value when \fBgl_get_line()\fR returns \fINULL\fR, the callback function should set \fBerrno\fR appropriately. .RE .sp .ne 2 .na \fB\fBGLFD_REFRESH\fR\fR .ad .RS 17n Redraw the input line then continue waiting for input. Return this if your callback wrote to the terminal. .RE .sp .ne 2 .na \fB\fBGLFD_CONTINUE\fR\fR .ad .RS 17n Continue to wait for input, without redrawing the line. .RE .sp .LP Note that before calling the callback, \fBgl_get_line()\fR blocks most signals and leaves its own signal handlers installed, so if you need to catch a particular signal you will need to both temporarily install your own signal handler, and unblock the signal. Be sure to re-block the signal (if it was originally blocked) and reinstate the original signal handler, if any, before returning. .sp .LP Your callback should not try to read from the terminal, which is left in raw mode as far as input is concerned. You can write to the terminal as usual, since features like conversion of newline to carriage-return/linefeed are re-enabled while the callback is running. If your callback function does write to the terminal, be sure to output a newline first, and when your callback returns, tell \fBgl_get_line()\fR that the input line needs to be redrawn, by returning the \fBGLFD_REFRESH\fR status code. .sp .LP To remove a callback function that you previously registered for a given file descriptor and event, simply call \fBgl_watch_fd()\fR with the same \fIfd\fR and \fIevent\fR arguments, but with a \fIcallback\fR argument of 0. The \fIdata\fR argument is ignored in this case. .SS "Setting An Inactivity Timeout" .sp .LP The \fBgl_inactivity_timeout()\fR 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 \fBgl_watch_fd()\fR. .sp .LP The timeout is specified in the form of an integral number of seconds and an integral number of nanoseconds, specified by the \fIsec\fR and \fInsec\fR arguments, respectively. Subsequently, whenever no activity is seen for this time period, the function specified by the \fIcallback\fR argument is called. The \fIdata\fR argument of \fBgl_inactivity_timeout()\fR is passed to this callback function whenever it is invoked, and can thus be used to pass arbitrary application-specific information to the callback. The following macro is provided in <\fBlibtecla.h\fR> for applications to use to declare and prototype timeout callback functions. .sp .in +2 .nf #define GL_TIMEOUT_FN(fn) GlAfterTimeout (fn)(GetLine *gl, void *data) .fi .in -2 .sp .LP On returning, the application's callback is expected to return one of the following enumerators to tell \fBgl_get_line()\fR how to procede after the timeout has been handled by the callback. .sp .ne 2 .na \fB\fBGLTO_ABORT\fR\fR .ad .RS 17n Tell \fBgl_get_line()\fR to abort. When this happens, \fBgl_get_line()\fR will return \fINULL\fR, and a following call to \fBgl_return_status()\fR will return \fBGLR_TIMEOUT\fR. Note that if the application needs \fBerrno\fR always to have a meaningful value when \fBgl_get_line()\fR returns \fINULL\fR, the callback function should set \fBerrno\fR appropriately. .RE .sp .ne 2 .na \fB\fBGLTO_REFRESH\fR\fR .ad .RS 17n Redraw the input line, then continue waiting for input. You should return this value if your callback wrote to the terminal. .RE .sp .ne 2 .na \fB\fBGLTO_CONTINUE\fR\fR .ad .RS 17n 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 \fBgl_io_mode\fR(3TECLA)), \fBgl_get_line()\fR acts as though I/O blocked. This means that \fBgl_get_line()\fR will immediately return \fINULL\fR, and a following call to \fBgl_return_status()\fR will return \fBGLR_BLOCKED\fR. .RE .sp .LP Note that before calling the callback, \fBgl_get_line()\fR blocks most signals and leaves its own signal handlers installed, so if you need to catch a particular signal you will need to both temporarily install your own signal handler and unblock the signal. Be sure to re-block the signal (if it was originally blocked) and reinstate the original signal handler, if any, before returning. .sp .LP Your callback should not try to read from the terminal, which is left in raw mode as far as input is concerned. You can however write to the terminal as usual, since features like conversion of newline to carriage-return/linefeed are re-enabled while the callback is running. If your callback function does write to the terminal, be sure to output a newline first, and when your callback returns, tell \fBgl_get_line()\fR that the input line needs to be redrawn, by returning the \fBGLTO_REFRESH\fR status code. .sp .LP Finally, note that although the timeout arguments include a nanosecond component, few computer clocks presently have resolutions that are finer than a few milliseconds, so asking for less than a few milliseconds is equivalent to requesting zero seconds on many systems. If this would be a problem, you should base your timeout selection on the actual resolution of the host clock (for example, by calling \fBsysconf\fR(\fB_SC_CLK_TCK\fR)). .sp .LP To turn off timeouts, simply call \fBgl_inactivity_timeout()\fR with a \fIcallback\fR argument of 0. The \fIdata\fR argument is ignored in this case. .SS "Signal Handling Defaults" .sp .LP By default, the \fBgl_get_line()\fR function intercepts a number of signals. This is particularly important for signals that would by default terminate the process, since the terminal needs to be restored to a usable state before this happens. This section describes the signals that are trapped by default and how \fBgl_get_line()\fR responds to them. Changing these defaults is the topic of the following section. .sp .LP When the following subset of signals are caught, \fBgl_get_line()\fR first restores the terminal settings and signal handling to how they were before \fBgl_get_line()\fR was called, resends the signal to allow the calling application's signal handlers to handle it, then, if the process still exists, returns \fINULL\fR and sets \fBerrno\fR as specified below. .sp .ne 2 .na \fB\fBSIGINT\fR\fR .ad .RS 11n This signal is generated both by the keyboard interrupt key (usually \fB^C\fR), and the keyboard break key. The \fBerrno\fR value is \fBEINTR\fR. .RE .sp .ne 2 .na \fB\fBSIGHUP\fR\fR .ad .RS 11n This signal is generated when the controlling terminal exits. The \fBerrno\fR value is \fBENOTTY\fR. .RE .sp .ne 2 .na \fB\fBSIGPIPE\fR\fR .ad .RS 11n This signal is generated when a program attempts to write to a pipe whose remote end is not being read by any process. This can happen for example if you have called \fBgl_change_terminal()\fR to redirect output to a pipe hidden under a pseudo terminal. The \fBerrno\fR value is \fBEPIPE\fR. .RE .sp .ne 2 .na \fB\fBSIGQUIT\fR\fR .ad .RS 11n This signal is generated by the keyboard quit key (usually \fB^\\fR). The \fBerrno\fR value is \fBEINTR\fR. .RE .sp .ne 2 .na \fB\fBSIGABRT\fR\fR .ad .RS 11n This signal is generated by the standard C, abort function. By default it both terminates the process and generates a core dump. The \fBerrno\fR value is \fBEINTR\fR. .RE .sp .ne 2 .na \fB\fBSIGTERM\fR\fR .ad .RS 11n This is the default signal that the UNIX kill command sends to processes. The \fBerrno\fR value is \fBEINTR\fR. .RE .sp .LP 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 \fBSIGQUIT\fR signal. In other words, if the calling application does not override the default handler by supplying its own signal handler, receipt of the corresponding signal will terminate the application before \fBgl_get_line()\fR returns. .sp .LP If \fBgl_get_line()\fR aborts with \fBerrno\fR set to \fBEINTR\fR, you can find out what signal caused it to abort, by calling the \fBgl_last_signal()\fR function. This returns the numeric code (for example, \fBSIGINT\fR) of the last signal that was received during the most recent call to \fBgl_get_line()\fR, or -1 if no signals were received. .sp .LP On systems that support it, when a \fBSIGWINCH\fR (window change) signal is received, \fBgl_get_line()\fR queries the terminal to find out its new size, redraws the current input line to accomodate the new size, then returns to waiting for keyboard input from the user. Unlike other signals, this signal is not resent to the application. .sp .LP Finally, the following signals cause \fBgl_get_line()\fR to first restore the terminal and signal environment to that which prevailed before \fBgl_get_line()\fR was called, then resend the signal to the application. If the process still exists after the signal has been delivered, then \fBgl_get_line()\fR then re-establishes its own signal handlers, switches the terminal back to raw mode, redisplays the input line, and goes back to awaiting terminal input from the user. .sp .ne 2 .na \fB\fBSIGCONT\fR\fR .ad .RS 13n This signal is generated when a suspended process is resumed. .RE .sp .ne 2 .na \fB\fBSIGPOLL\fR\fR .ad .RS 13n On SVR4 systems, this signal notifies the process of an asynchronous I/O event. Note that under 4.3+BSD, \fBSIGIO\fR and \fBSIGPOLL\fR are the same. On other systems, \fBSIGIO\fR is ignored by default, so \fBgl_get_line()\fR does not trap it by default. .RE .sp .ne 2 .na \fB\fBSIGPWR\fR\fR .ad .RS 13n This signal is generated when a power failure occurs (presumably when the system is on a UPS). .RE .sp .ne 2 .na \fB\fBSIGALRM\fR\fR .ad .RS 13n This signal is generated when a timer expires. .RE .sp .ne 2 .na \fB\fBSIGUSR1\fR\fR .ad .RS 13n An application specific signal. .RE .sp .ne 2 .na \fB\fBSIGUSR2\fR\fR .ad .RS 13n Another application specific signal. .RE .sp .ne 2 .na \fB\fBSIGVTALRM\fR\fR .ad .RS 13n This signal is generated when a virtual timer expires. See \fBsetitimer\fR(2). .RE .sp .ne 2 .na \fB\fBSIGXCPU\fR\fR .ad .RS 13n This signal is generated when a process exceeds its soft CPU time limit. .RE .sp .ne 2 .na \fB\fBSIGXFSZ\fR\fR .ad .RS 13n This signal is generated when a process exceeds its soft file-size limit. .RE .sp .ne 2 .na \fB\fBSIGTSTP\fR\fR .ad .RS 13n This signal is generated by the terminal suspend key, which is usually \fB^Z\fR, or the delayed terminal suspend key, which is usually \fB^Y\fR. .RE .sp .ne 2 .na \fB\fBSIGTTIN\fR\fR .ad .RS 13n This signal is generated if the program attempts to read from the terminal while the program is running in the background. .RE .sp .ne 2 .na \fB\fBSIGTTOU\fR\fR .ad .RS 13n This signal is generated if the program attempts to write to the terminal while the program is running in the background. .RE .sp .LP Obviously not all of the above signals are supported on all systems, so code to support them is conditionally compiled into the tecla library. .sp .LP Note that if \fBSIGKILL\fR or \fBSIGPOLL\fR, which by definition cannot be caught, or any of the hardware generated exception signals, such as \fBSIGSEGV\fR, \fBSIGBUS\fR, and \fBSIGFPE\fR, are received and unhandled while \fBgl_get_line()\fR 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. .SS "Customized Signal Handling" .sp .LP The previous section listed the signals that \fBgl_get_line()\fR 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 \fBgl_get_line()\fR should respond to a given signal. .sp .LP If you do not need \fBgl_get_line()\fR to do anything in response to a signal that it normally traps, you can tell to \fBgl_get_line()\fR to ignore that signal by calling \fBgl_ignore_signal()\fR. .sp .LP The \fIsigno\fR argument is the number of the signal (for example, \fBSIGINT\fR) that you want to have ignored. If the specified signal is not currently one of those being trapped, this function does nothing. .sp .LP The \fBgl_trap_signal()\fR function allows you to either add a new signal to the list that \fBgl_get_line()\fR traps or modify how it responds to a signal that it already traps. .sp .LP The \fIsigno\fR argument is the number of the signal that you want to have trapped. The \fIflags\fR argument is a set of flags that determine the environment in which the application's signal handler is invoked. The \fIafter\fR argument tells \fBgl_get_line()\fR what to do after the application's signal handler returns. The \fIerrno_value\fR tells \fBgl_get_line()\fR what to set \fBerrno\fR to if told to abort. .sp .LP The \fIflags\fR argument is a bitwise OR of zero or more of the following enumerators: .sp .ne 2 .na \fB\fBGLS_RESTORE_SIG\fR\fR .ad .RS 20n Restore the caller's signal environment while handling the signal. .RE .sp .ne 2 .na \fB\fBGLS_RESTORE_TTY\fR\fR .ad .RS 20n Restore the caller's terminal settings while handling the signal. .RE .sp .ne 2 .na \fB\fBGLS_RESTORE_LINE\fR\fR .ad .RS 20n Move the cursor to the start of the line following the input line before invoking the application's signal handler. .RE .sp .ne 2 .na \fB\fBGLS_REDRAW_LINE\fR\fR .ad .RS 20n Redraw the input line when the application's signal handler returns. .RE .sp .ne 2 .na \fB\fBGLS_UNBLOCK_SIG\fR\fR .ad .RS 20n Normally, if the calling program has a signal blocked (see \fBsigprocmask\fR(2)), \fBgl_get_line()\fR does not trap that signal. This flag tells \fBgl_get_line()\fR to trap the signal and unblock it for the duration of the call to \fBgl_get_line()\fR. .RE .sp .ne 2 .na \fB\fBGLS_DONT_FORWARD\fR\fR .ad .RS 20n If this flag is included, the signal will not be forwarded to the signal handler of the calling program. .RE .sp .LP Two commonly useful flag combinations are also enumerated as follows: .sp .ne 2 .na \fB\fBGLS_RESTORE_ENV\fR\fR .ad .RS 21n \fBGLS_RESTORE_SIG\fR | \fBGLS_RESTORE_TTY\fR |\fBGLS_REDRAW_LINE\fR .RE .sp .ne 2 .na \fB\fBGLS_SUSPEND_INPUT\fR\fR .ad .RS 21n \fBGLS_RESTORE_ENV\fR | \fBGLS_RESTORE_LINE\fR .RE .sp .LP If your signal handler, or the default system signal handler for this signal, if you have not overridden it, never either writes to the terminal, nor suspends or terminates the calling program, then you can safely set the \fIflags\fR argument to 0. .RS +4 .TP .ie t \(bu .el o The cursor does not get left in the middle of the input line. .RE .RS +4 .TP .ie t \(bu .el o So that the user can type in input and have it echoed. .RE .RS +4 .TP .ie t \(bu .el o So that you do not need to end each output line with \er\en, instead of just \en. .RE .sp .LP The \fBGL_RESTORE_ENV\fR combination is the same as \fBGL_SUSPEND_INPUT\fR, except that it does not move the cursor. If your signal handler does not read or write anything to the terminal, the user will not see any visible indication that a signal was caught. This can be useful if you have a signal handler that only occasionally writes to the terminal, where using \fBGL_SUSPEND_LINE\fR would cause the input line to be unnecessarily duplicated when nothing had been written to the terminal. Such a signal handler, when it does write to the terminal, should be sure to start a new line at the start of its first write, by writing a new line before returning. If the signal arrives while the user is entering a line that only occupies a signal terminal line, or if the cursor is on the last terminal line of a longer input line, this will have the same effect as \fBGL_SUSPEND_INPUT\fR. Otherwise it will start writing on a line that already contains part of the displayed input line. This does not do any harm, but it looks a bit ugly, which is why the \fBGL_SUSPEND_INPUT\fR combination is better if you know that you are always going to be writting to the terminal. .sp .LP The \fIafter\fR argument, which determines what \fBgl_get_line()\fR does after the application's signal handler returns (if it returns), can take any one of the following values: .sp .ne 2 .na \fB\fBGLS_RETURN\fR\fR .ad .RS 16n Return the completed input line, just as though the user had pressed the return key. .RE .sp .ne 2 .na \fB\fBGLS_ABORT\fR\fR .ad .RS 16n Cause \fBgl_get_line()\fR to abort. When this happens, \fBgl_get_line()\fR returns \fINULL\fR, and a following call to \fBgl_return_status()\fR will return \fBGLR_SIGNAL\fR. Note that if the application needs \fBerrno\fR always to have a meaningful value when \fBgl_get_line()\fR returns \fINULL\fR, the callback function should set \fBerrno\fR appropriately. .RE .sp .ne 2 .na \fB\fBGLS_CONTINUE\fR\fR .ad .RS 16n Resume command line editing. .RE .sp .LP The \fIerrno_value\fR argument is intended to be combined with the \fBGLS_ABORT\fR option, telling \fBgl_get_line()\fR what to set the standard \fBerrno\fR variable to before returning \fINULL\fR to the calling program. It can also, however, be used with the \fBGL_RETURN\fR option, in case you want to have a way to distinguish between an input line that was entered using the return key, and one that was entered by the receipt of a signal. .SS "Reliable Signal Handling" .sp .LP Signal handling is suprisingly hard to do reliably without race conditions. In \fBgl_get_line()\fR a lot of care has been taken to allow applications to perform reliable signal handling around \fBgl_get_line()\fR. This section explains how to make use of this. .sp .LP As an example of the problems that can arise if the application is not written correctly, imagine that one's application has a \fBSIGINT\fR signal handler that sets a global flag. Now suppose that the application tests this flag just before invoking \fBgl_get_line()\fR. If a \fBSIGINT\fR 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 \fBgl_get_line()\fR, then \fBgl_get_line()\fR will not see the signal, and will not be interrupted. As a result, the application will not be able to respond to the signal until the user gets around to finishing entering the input line and \fBgl_get_line()\fR returns. Depending on the application, this might or might not be a disaster, but at the very least it would puzzle the user. .sp .LP The way to avoid such problems is to do the following. .RS +4 .TP 1. If needed, use the \fBgl_trap_signal()\fR function to configure \fBgl_get_line()\fR to abort when important signals are caught. .RE .RS +4 .TP 2. Configure \fBgl_get_line()\fR such that if any of the signals that it catches are blocked when \fBgl_get_line()\fR is called, they will be unblocked automatically during times when \fBgl_get_line()\fR is waiting for I/O. This can be done either on a per signal basis, by calling the \fBgl_trap_signal()\fR function, and specifying the \fBGLS_UNBLOCK\fR attribute of the signal, or globally by calling the \fBgl_catch_blocked()\fR function. This function simply adds the \fBGLS_UNBLOCK\fR attribute to all of the signals that it is currently configured to trap. .RE .RS +4 .TP 3. Just before calling \fBgl_get_line()\fR, block delivery of all of the signals that \fBgl_get_line()\fR is configured to trap. This can be done using the POSIX sigprocmask function in conjunction with the \fBgl_list_signals()\fR function. This function returns the set of signals that it is currently configured to catch in the set argument, which is in the form required by \fBsigprocmask\fR(2). .RE .RS +4 .TP 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 \fBgl_get_line()\fR unblocks its signals while performing I/O. .RE .RS +4 .TP 5. Eventually \fBgl_get_line()\fR returns, either because a signal was caught, an error occurred, or the user finished entering their input line. .RE .RS +4 .TP 6. Now one would check the global signal flag again, and if it is set, respond to it, and zero the flag. .RE .RS +4 .TP 7. Use \fBsigprocmask()\fR to unblock the signals that were blocked in step 3. .RE .sp .LP The same technique can be used around certain POSIX signal-aware functions, such as \fBsigsetjmp\fR(3C) and \fBsigsuspend\fR(2), and in particular, the former of these two functions can be used in conjunction with \fBsiglongjmp\fR(3C) to implement race-condition free signal handling around other long-running system calls. The \fBgl_get_line()\fR function manages to reliably trap signals around calls to functions like \fBread\fR(2) and \fBselect\fR(3C) without race conditions. .sp .LP The \fBgl_get_line()\fR function first uses the POSIX \fBsigprocmask()\fR 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. .sp .LP Whenever \fBgl_get_line()\fR needs to call read or select to wait for input from the user, it first calls the POSIX \fBsigsetjmp()\fR function, being sure to specify a non-zero value for its \fIsavemask\fR argument. .sp .LP If \fBsigsetjmp()\fR returns zero, \fBgl_get_line()\fR then does the following. .RS +4 .TP 1. It uses the POSIX \fBsigaction\fR(2) function to register a temporary signal handler to all of the signals that it is configured to catch. This signal handler does two things. .RS +4 .TP a. It records the number of the signal that was received in a file-scope variable. .RE .RS +4 .TP b. It then calls the POSIX \fBsiglongjmp()\fR function using the buffer that was passed to \fBsigsetjmp()\fR for its first argument and a non-zero value for its second argument. .RE When this signal handler is registered, the \fIsa_mask\fR member of the \fBstruct sigaction\fR \fIact\fR argument of the call to \fBsigaction()\fR is configured to contain all of the signals that \fBgl_get_line()\fR is catching. This ensures that only one signal will be caught at once by our signal handler, which in turn ensures that multiple instances of our signal handler do not tread on each other's toes. .RE .RS +4 .TP 2. Now that the signal handler has been set up, \fBgl_get_line()\fR unblocks all of the signals that it is configured to catch. .RE .RS +4 .TP 3. It then calls the \fBread()\fR or \fBselect()\fR function to wait for keyboard input. .RE .RS +4 .TP 4. If this function returns (that is, no signal is received), \fBgl_get_line()\fR blocks delivery of the signals of interest again. .RE .RS +4 .TP 5. It then reinstates the signal handlers that were displaced by the one that was just installed. .RE .sp .LP Alternatively, if \fBsigsetjmp()\fR returns non-zero, this means that one of the signals being trapped was caught while the above steps were executing. When this happens, \fBgl_get_line()\fR does the following. .sp .LP First, note that when a call to \fBsiglongjmp()\fR causes \fBsigsetjmp()\fR to return, provided that the \fIsavemask\fR argument of \fBsigsetjmp()\fR was non-zero, the signal process mask is restored to how it was when \fBsigsetjmp()\fR was called. This is the important difference between \fBsigsetjmp()\fR and the older problematic \fBsetjmp\fR(3C), 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 \fBsigsetjmp()\fR 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. .RS +4 .TP 1. If so instructed by the \fBgl_get_line()\fR configuration attributes of the signal that was caught, \fBgl_get_line()\fR restores the terminal attributes to the state that they had when \fBgl_get_line()\fR 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. .RE .RS +4 .TP 2. It then reinstates the application's signal handlers. .RE .RS +4 .TP 3. Then it uses the C standard-library \fBraise\fR(3C) function to re-send the application the signal that was caught. .RE .RS +4 .TP 4. Next it unblocks delivery of the signal that we just sent. This results in the signal that was just sent by \fBraise()\fR being caught by the application's original signal handler, which can now handle it as it sees fit. .RE .RS +4 .TP 5. If the signal handler returns (that is, it does not terminate the process), \fBgl_get_line()\fR blocks delivery of the above signal again. .RE .RS +4 .TP 6. It then undoes any actions performed in the first of the above steps and redisplays the line, if the signal configuration calls for this. .RE .RS +4 .TP 7. \fBgl_get_line()\fR then either resumes trying to read a character, or aborts, depending on the configuration of the signal that was caught. .RE .sp .LP 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 \fBgl_get_line()\fR has complete control over its environment. .SS "The Terminal Size" .sp .LP On most systems the combination of the \fBTIOCGWINSZ\fR ioctl and the \fBSIGWINCH\fR signal is used to maintain an accurate idea of the terminal size. The terminal size is newly queried every time that \fBgl_get_line()\fR is called and whenever a \fBSIGWINCH\fR signal is received. .sp .LP On the few systems where this mechanism is not available, at startup \fBnew_GetLine()\fR first looks for the \fBLINES\fR and \fBCOLUMNS\fR environment variables. If these are not found, or they contain unusable values, then if a terminal information database like \fBterminfo\fR or \fBtermcap\fR is available, the default size of the terminal is looked up in this database. If this too fails to provide the terminal size, a default size of 80 columns by 24 lines is used. .sp .LP Even on systems that do support ioctl(\fBTIOCGWINSZ\fR), 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 \fBSIGWINCH\fR is sent to the process, and the dimensions returned by ioctl(\fBTIOCGWINSZ\fR) are not correct. The only way to handle such instances is to provide a way for the user to enter a command that tells the remote system what the new size is. This command would then call the \fBgl_set_term_size()\fR function to tell \fBgl_get_line()\fR about the change in size. .sp .LP The \fIncolumn\fR and \fInline\fR arguments are used to specify the new dimensions of the terminal, and must not be less than 1. On systems that do support ioctl(\fBTIOCGWINSZ\fR), this function first calls ioctl(\fBTIOCSWINSZ\fR) to tell the terminal driver about the change in size. In non-blocking server-I/O mode, if a line is currently being input, the input line is then redrawn to accomodate the changed size. Finally the new values are recorded in \fIgl\fR for future use by \fBgl_get_line()\fR. .sp .LP The \fBgl_terminal_size()\fR function allows you to query the current size of the terminal, and install an alternate fallback size for cases where the size is not available. Beware that the terminal size will not be available if reading from a pipe or a file, so the default values can be important even on systems that do support ways of finding out the terminal size. .sp .LP This function first updates \fBgl_get_line()\fR's fallback terminal dimensions, then records its findings in the return value. .sp .LP The \fIdef_ncolumn\fR and \fIdef_nline\fR arguments specify the default number of terminal columns and lines to use if the terminal size cannot be determined by ioctl(\fBTIOCGWINSZ\fR) or environment variables. .SS "Hiding What You Type" .sp .LP 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 \fBgl_echo_mode()\fR function allows you to toggle on and off the display and archival of any text that is subsequently entered in calls to \fBgl_get_line()\fR. .sp .LP The \fIenable\fR argument specifies whether entered text should be visible or not. If it is 0, then subsequently entered lines will not be visible on the terminal, and will not be recorded in the history list. If it is 1, then subsequent input lines will be displayed as they are entered, and provided that history has not been turned off with a call to \fBgl_toggle_history()\fR, 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 through the return value. In all cases, the return value of the function is 0 if echoing was disabled before the function was called, and 1 if it was enabled. .sp .LP 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. .SS "Single Character Queries" .sp .LP Using \fBgl_get_line()\fR 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 \fBgl_query_char()\fR function has been provided for single character queries like this. .sp .LP 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, \fBgl_query_char()\fR 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 \fBgl_return_status()\fR, to find out what went wrong. This could, for example, have been the reception of a signal, or the optional inactivity timer going off. .sp .LP If the user simply hits enter, the value of the \fIdefchar\fR argument is substituted. This means that when the user hits either newline or return, the character specified in \fIdefchar\fR, 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 '\en' as the value of \fIdefchar\fR. .sp .LP If the entered character is an unprintable character, it is displayed symbolically. For example, control-A is displayed as \fB^A\fR, and characters beyond 127 are displayed in octal, preceded by a backslash. .sp .LP As with \fBgl_get_line()\fR, echoing of the entered character can be disabled using the \fBgl_echo_mode()\fR function. .sp .LP 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 \fBgl_query_char()\fR resumes waiting for the user to type a character. .sp .LP Note that in non-blocking server mode, if an incomplete input line is in the process of being read when \fBgl_query_char()\fR is called, the partial input line is discarded, and erased from the terminal, before the new prompt is displayed. The next call to \fBgl_get_line()\fR will thus start editing a new line. .SS "Reading Raw Characters" .sp .LP Whereas the \fBgl_query_char()\fR function visibly prompts the user for a character, and displays what they typed, the \fBgl_read_char()\fR 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 \fBgl_get_line()\fR, but also from callback functions that the application has registered to be called by \fBgl_get_line()\fR. .sp .LP On success, the return value of \fBgl_read_char()\fR is the character that was read. On failure, EOF is returned, and the \fBgl_return_status()\fR 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 \fBgl_get_line()\fR, or terminal I/O blocking, when in non-blocking server-I/O mode. .sp .LP Beware that certain keyboard keys, such as function keys, and cursor keys, usually generate at least three characters each, so a single call to \fBgl_read_char()\fR will not be enough to identify such keystrokes. .SS "Clearing The Terminal" .sp .LP The calling program can clear the terminal by calling \fBgl_erase_terminal()\fR. In non-blocking server-I/O mode, this function also arranges for the current input line to be redrawn from scratch when \fBgl_get_line()\fR is next called. .SS "Displaying Text Dynamically" .sp .LP Between calls to \fBgl_get_line()\fR, the \fBgl_display_text()\fR function provides a convenient way to display paragraphs of text, left-justified and split over one or more terminal lines according to the constraints of the current width of the terminal. Examples of the use of this function may be found in the demo programs, where it is used to display introductions. In those examples the advanced use of optional prefixes, suffixes and filled lines to draw a box around the text is also illustrated. .sp .LP If \fIgl\fR is not currently connected to a terminal, for example if the output of a program that uses \fBgl_get_line()\fR is being piped to another program or redirected to a file, then the value of the \fIdef_width\fR parameter is used as the terminal width. .sp .LP The \fIindentation\fR argument specifies the number of characters to use to indent each line of ouput. The \fIfill_char\fR argument specifies the character that will be used to perform this indentation. .sp .LP The \fIprefix\fR argument can be either \fINULL\fR or a string to place at the beginning of each new line (after any indentation). Similarly, the \fIsuffix\fR argument can be either \fINULL\fR or 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 by the \fIfill_char\fR argument. Normally the fill-character is a space. .sp .LP The \fIstart\fR argument tells \fBgl_display_text()\fR 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 \fBgl_display_text()\fR 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 \fBgl_display_text()\fR 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. .sp .LP On error, \fBgl_display_text()\fR returns -1. .SS "Callback Function Facilities" .sp .LP Unless otherwise stated, callback functions such as tab completion callbacks and event callbacks should not call any functions in this module. The following functions, however, are designed specifically to be used by callback functions. .sp .LP Calling the \fBgl_replace_prompt()\fR function from a callback tells \fBgl_get_line()\fR to display a different prompt when the callback returns. Except in non-blocking server mode, it has no effect if used between calls to \fBgl_get_line()\fR. In non-blocking server mode, when used between two calls to \fBgl_get_line()\fR 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 \fBgl_get_line()\fR. .SS "International Character Sets" .sp .LP Since \fBlibtecla\fR(3LIB) version 1.4.0, \fBgl_get_line()\fR has been 8-bit clean. This means that all 8-bit characters that are printable in the user's current locale are now displayed verbatim and included in the returned input line. Assuming that the calling program correctly contains a call like the following, .sp .in +2 .nf setlocale(LC_CTYPE, "") .fi .in -2 .sp .LP then the current locale is determined by the first of the environment variables \fBLC_CTYPE\fR, \fBLC_ALL\fR, and \fBLANG\fR that is found to contain a valid locale name. If none of these variables are defined, or the program neglects to call \fBsetlocale\fR(3C), then the default C locale is used, which is US 7-bit ASCII. On most UNIX-like platforms, you can get a list of valid locales by typing the command: .sp .in +2 .nf locale -a .fi .in -2 .sp .sp .LP at the shell prompt. Further documentation on how the user can make use of this to enter international characters can be found in the \fBtecla\fR(5) man page. .SS "Thread Safety" .sp .LP Unfortunately neither \fBterminfo\fR nor \fBtermcap\fR were designed to be reentrant, so you cannot 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, it is safe to use this module from a single thread of a multi-threaded program, provided that your other threads do not use any \fBtermcap\fR or \fBterminfo\fR functions. .SH ATTRIBUTES .sp .LP See \fBattributes\fR(5) for descriptions of the following attributes: .sp .sp .TS box; c | c l | l . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Committed _ MT-Level MT-Safe .TE .SH SEE ALSO .sp .LP \fBcpl_complete_word\fR(3TECLA), \fBef_expand_file\fR(3TECLA), \fBgl_io_mode\fR(3TECLA), \fBlibtecla\fR(3LIB), \fBpca_lookup_file\fR(3TECLA), \fBattributes\fR(5), \fBtecla\fR(5)