1 This is Info file ./termcap.info, produced by Makeinfo-1.55 from the
2 input file ./termcap.texi.
4 This file documents the termcap library of the GNU system.
6 Copyright (C) 1988 Free Software Foundation, Inc.
8 Permission is granted to make and distribute verbatim copies of this
9 manual provided the copyright notice and this permission notice are
10 preserved on all copies.
12 Permission is granted to copy and distribute modified versions of
13 this manual under the conditions for verbatim copying, provided that
14 the entire resulting derived work is distributed under the terms of a
15 permission notice identical to this one.
17 Permission is granted to copy and distribute translations of this
18 manual into another language, under the above conditions for modified
19 versions, except that this permission notice may be stated in a
20 translation approved by the Foundation.
23 File: termcap.info, Node: Top, Next: Introduction, Prev: (dir), Up: (dir)
27 * Introduction:: What is termcap? Why this manual?
28 * Library:: The termcap library functions.
29 * Data Base:: What terminal descriptions in `/etc/termcap' look like.
30 * Capabilities:: Definitions of the individual terminal capabilities:
31 how to write them in descriptions, and how to use
32 their values to do display updating.
33 * Summary:: Brief table of capability names and their meanings.
34 * Var Index:: Index of C functions and variables.
35 * Cap Index:: Index of termcap capabilities.
36 * Index:: Concept index.
38 -- The Detailed Node Listing --
42 * Preparation:: Preparing to use the termcap library.
43 * Find:: Finding the description of the terminal being used.
44 * Interrogate:: Interrogating the description for particular capabilities.
45 * Initialize:: Initialization for output using termcap.
46 * Padding:: Outputting padding.
47 * Parameters:: Encoding parameters such as cursor positions.
51 * Why Pad:: Explanation of padding.
52 * Not Enough:: When there is not enough padding.
53 * Describe Padding:: The data base says how much padding a terminal needs.
54 * Output Padding:: Using `tputs' to output the needed padding.
58 * Encode Parameters:: The language for encoding parameters.
59 * Using Parameters:: Outputting a string command with parameters.
61 Sending Display Commands with Parameters
63 * tparam:: The general case, for GNU termcap only.
64 * tgoto:: The special case of cursor motion.
66 The Format of the Data Base
68 * Format:: Overall format of a terminal description.
69 * Capability Format:: Format of capabilities within a description.
70 * Naming:: Naming conventions for terminal types.
71 * Inheriting:: Inheriting part of a description from
72 a related terminal type.
73 * Changing:: When changes in the data base take effect.
75 Definitions of the Terminal Capabilities
77 * Basic:: Basic characteristics.
78 * Screen Size:: Screen size, and what happens when it changes.
79 * Cursor Motion:: Various ways to move the cursor.
80 * Wrapping:: What happens if you write a character in the last column.
81 * Scrolling:: Pushing text up and down on the screen.
82 * Windows:: Limiting the part of the window that output affects.
83 * Clearing:: Erasing one or many lines.
84 * Insdel Line:: Making new blank lines in mid-screen; deleting lines.
85 * Insdel Char:: Inserting and deleting characters within a line.
86 * Standout:: Highlighting some of the text.
87 * Underlining:: Underlining some of the text.
88 * Cursor Visibility:: Making the cursor more or less easy to spot.
89 * Bell:: Attracts user's attention; not localized on the screen.
90 * Keypad:: Recognizing when function keys or arrows are typed.
91 * Meta Key:: META acts like an extra shift key.
92 * Initialization:: Commands used to initialize or reset the terminal.
93 * Pad Specs:: Info for the kernel on how much padding is needed.
94 * Status Line:: A status line displays "background" information.
95 * Half-Line:: Moving by half-lines, for superscripts and subscripts.
96 * Printer:: Controlling auxiliary printers of display terminals.
99 File: termcap.info, Node: Introduction, Next: Library, Prev: Top, Up: Top
104 "Termcap" is a library and data base that enables programs to use
105 display terminals in a terminal-independent manner. It originated in
108 The termcap data base describes the capabilities of hundreds of
109 different display terminals in great detail. Some examples of the
110 information recorded for a terminal could include how many columns wide
111 it is, what string to send to move the cursor to an arbitrary position
112 (including how to encode the row and column numbers), how to scroll the
113 screen up one or several lines, and how much padding is needed for such
114 a scrolling operation.
116 The termcap library is provided for easy access this data base in
117 programs that want to do terminal-independent character-based display
120 This manual describes the GNU version of the termcap library, which
121 has some extensions over the Unix version. All the extensions are
122 identified as such, so this manual also tells you how to use the Unix
125 The GNU version of the termcap library is available free as source
126 code, for use in free programs, and runs on Unix and VMS systems (at
127 least). You can find it in the GNU Emacs distribution in the files
128 `termcap.c' and `tparam.c'.
130 This manual was written for the GNU project, whose goal is to
131 develop a complete free operating system upward-compatible with Unix
132 for user programs. The project is approximately two thirds complete.
133 For more information on the GNU project, including the GNU Emacs editor
134 and the mostly-portable optimizing C compiler, send one dollar to
136 Free Software Foundation
141 File: termcap.info, Node: Library, Next: Data Base, Prev: Introduction, Up: Top
146 The termcap library is the application programmer's interface to the
147 termcap data base. It contains functions for the following purposes:
149 * Finding the description of the user's terminal type (`tgetent').
151 * Interrogating the description for information on various topics
152 (`tgetnum', `tgetflag', `tgetstr').
154 * Computing and performing padding (`tputs').
156 * Encoding numeric parameters such as cursor positions into the
157 terminal-specific form required for display commands (`tparam',
162 * Preparation:: Preparing to use the termcap library.
163 * Find:: Finding the description of the terminal being used.
164 * Interrogate:: Interrogating the description for particular capabilities.
165 * Initialize:: Initialization for output using termcap.
166 * Padding:: Outputting padding.
167 * Parameters:: Encoding parameters such as cursor positions.
170 File: termcap.info, Node: Preparation, Next: Find, Up: Library
172 Preparing to Use the Termcap Library
173 ====================================
175 To use the termcap library in a program, you need two kinds of
178 * The compiler needs declarations of the functions and variables in
181 On GNU systems, it suffices to include the header file `termcap.h'
182 in each source file that uses these functions and variables.
184 On Unix systems, there is often no such header file. Then you must
185 explictly declare the variables as external. You can do likewise
186 for the functions, or let them be implicitly declared and cast
187 their values from type `int' to the appropriate type.
189 We illustrate the declarations of the individual termcap library
190 functions with ANSI C prototypes because they show how to pass the
191 arguments. If you are not using the GNU C compiler, you probably
192 cannot use function prototypes, so omit the argument types and
193 names from your declarations.
195 * The linker needs to search the library. Usually either
196 `-ltermcap' or `-ltermlib' as an argument when linking will do
200 File: termcap.info, Node: Find, Next: Interrogate, Prev: Preparation, Up: Library
202 Finding a Terminal Description: `tgetent'
203 =========================================
205 An application program that is going to use termcap must first look
206 up the description of the terminal type in use. This is done by calling
207 `tgetent', whose declaration in ANSI Standard C looks like:
209 int tgetent (char *BUFFER, char *TERMTYPE);
211 This function finds the description and remembers it internally so that
212 you can interrogate it about specific terminal capabilities (*note
215 The argument TERMTYPE is a string which is the name for the type of
216 terminal to look up. Usually you would obtain this from the environment
217 variable `TERM' using `getenv ("TERM")'.
219 If you are using the GNU version of termcap, you can alternatively
220 ask `tgetent' to allocate enough space. Pass a null pointer for
221 BUFFER, and `tgetent' itself allocates the storage using `malloc'.
222 There is no way to get the address that was allocated, and you
223 shouldn't try to free the storage.
225 With the Unix version of termcap, you must allocate space for the
226 description yourself and pass the address of the space as the argument
227 BUFFER. There is no way you can tell how much space is needed, so the
228 convention is to allocate a buffer 2048 characters long and assume that
229 is enough. (Formerly the convention was to allocate 1024 characters and
230 assume that was enough. But one day, for one kind of terminal, that was
233 No matter how the space to store the description has been obtained,
234 termcap records its address internally for use when you later
235 interrogate the description with `tgetnum', `tgetstr' or `tgetflag'. If
236 the buffer was allocated by termcap, it will be freed by termcap too if
237 you call `tgetent' again. If the buffer was provided by you, you must
238 make sure that its contents remain unchanged for as long as you still
239 plan to interrogate the description.
241 The return value of `tgetent' is -1 if there is some difficulty
242 accessing the data base of terminal types, 0 if the data base is
243 accessible but the specified type is not defined in it, and some other
246 Here is how you might use the function `tgetent':
249 static char term_buffer[2048];
251 #define term_buffer 0
254 init_terminal_data ()
256 char *termtype = getenv ("TERM");
260 fatal ("Specify a terminal type with `setenv TERM <yourtype>'.\n");
262 success = tgetent (term_buffer, termtype);
264 fatal ("Could not access the termcap data base.\n");
266 fatal ("Terminal type `%s' is not defined.\n", termtype);
269 Here we assume the function `fatal' prints an error message and exits.
271 If the environment variable `TERMCAP' is defined, its value is used
272 to override the terminal type data base. The function `tgetent' checks
273 the value of `TERMCAP' automatically. If the value starts with `/'
274 then it is taken as a file name to use as the data base file, instead
275 of `/etc/termcap' which is the standard data base. If the value does
276 not start with `/' then it is itself used as the terminal description,
277 provided that the terminal type TERMTYPE is among the types it claims
278 to apply to. *Note Data Base::, for information on the format of a
279 terminal description.
282 File: termcap.info, Node: Interrogate, Next: Initialize, Prev: Find, Up: Library
284 Interrogating the Terminal Description
285 ======================================
287 Each piece of information recorded in a terminal description is
288 called a "capability". Each defined terminal capability has a
289 two-letter code name and a specific meaning. For example, the number
290 of columns is named `co'. *Note Capabilities::, for definitions of all
291 the standard capability names.
293 Once you have found the proper terminal description with `tgetent'
294 (*note Find::.), your application program must "interrogate" it for
295 various terminal capabilities. You must specify the two-letter code of
296 the capability whose value you seek.
298 Capability values can be numeric, boolean (capability is either
299 present or absent) or strings. Any particular capability always has
300 the same value type; for example, `co' always has a numeric value,
301 while `am' (automatic wrap at margin) is always a flag, and `cm'
302 (cursor motion command) always has a string value. The documentation
303 of each capability says which type of value it has.
305 There are three functions to use to get the value of a capability,
306 depending on the type of value the capability has. Here are their
307 declarations in ANSI C:
309 int tgetnum (char *NAME);
310 int tgetflag (char *NAME);
311 char *tgetstr (char *NAME, char **AREA);
314 Use `tgetnum' to get a capability value that is numeric. The
315 argument NAME is the two-letter code name of the capability. If
316 the capability is present, `tgetnum' returns the numeric value
317 (which is nonnegative). If the capability is not mentioned in the
318 terminal description, `tgetnum' returns -1.
321 Use `tgetflag' to get a boolean value. If the capability NAME is
322 present in the terminal description, `tgetflag' returns 1;
323 otherwise, it returns 0.
326 Use `tgetstr' to get a string value. It returns a pointer to a
327 string which is the capability value, or a null pointer if the
328 capability is not present in the terminal description.
330 There are two ways `tgetstr' can find space to store the string
333 * You can ask `tgetstr' to allocate the space. Pass a null
334 pointer for the argument AREA, and `tgetstr' will use
335 `malloc' to allocate storage big enough for the value.
336 Termcap will never free this storage or refer to it again; you
337 should free it when you are finished with it.
339 This method is more robust, since there is no need to guess
340 how much space is needed. But it is supported only by the GNU
343 * You can provide the space. Provide for the argument AREA the
344 address of a pointer variable of type `char *'. Before
345 calling `tgetstr', initialize the variable to point at
346 available space. Then `tgetstr' will store the string value
347 in that space and will increment the pointer variable to
348 point after the space that has been used. You can use the
349 same pointer variable for many calls to `tgetstr'.
351 There is no way to determine how much space is needed for a
352 single string, and no way for you to prevent or handle
353 overflow of the area you have provided. However, you can be
354 sure that the total size of all the string values you will
355 obtain from the terminal description is no greater than the
356 size of the description (unless you get the same capability
357 twice). You can determine that size with `strlen' on the
358 buffer you provided to `tgetent'. See below for an example.
360 Providing the space yourself is the only method supported by
361 the Unix version of termcap.
363 Note that you do not have to specify a terminal type or terminal
364 description for the interrogation functions. They automatically use the
365 description found by the most recent call to `tgetent'.
367 Here is an example of interrogating a terminal description for
368 various capabilities, with conditionals to select between the Unix and
369 GNU methods of providing buffer space.
373 char *cl_string, *cm_string;
378 char PC; /* For tputs. */
379 char *BC; /* For tgoto. */
382 interrogate_terminal ()
385 /* Here we assume that an explicit term_buffer
386 was provided to tgetent. */
388 = (char *) malloc (strlen (term_buffer));
389 #define BUFFADDR &buffer
396 /* Extract information we will use. */
397 cl_string = tgetstr ("cl", BUFFADDR);
398 cm_string = tgetstr ("cm", BUFFADDR);
399 auto_wrap = tgetflag ("am");
400 height = tgetnum ("li");
401 width = tgetnum ("co");
403 /* Extract information that termcap functions use. */
404 temp = tgetstr ("pc", BUFFADDR);
405 PC = temp ? *temp : 0;
406 BC = tgetstr ("le", BUFFADDR);
407 UP = tgetstr ("up", BUFFADDR);
410 *Note Padding::, for information on the variable `PC'. *Note Using
411 Parameters::, for information on `UP' and `BC'.
414 File: termcap.info, Node: Initialize, Next: Padding, Prev: Interrogate, Up: Library
416 Initialization for Use of Termcap
417 =================================
419 Before starting to output commands to a terminal using termcap, an
420 application program should do two things:
422 * Initialize various global variables which termcap library output
423 functions refer to. These include `PC' and `ospeed' for padding
424 (*note Output Padding::.) and `UP' and `BC' for cursor motion
427 * Tell the kernel to turn off alteration and padding of
428 horizontal-tab characters sent to the terminal.
430 To turn off output processing in Berkeley Unix you would use `ioctl'
431 with code `TIOCLSET' to set the bit named `LLITOUT', and clear the bits
432 `ANYDELAY' using `TIOCSETN'. In POSIX or System V, you must clear the
433 bit named `OPOST'. Refer to the system documentation for details.
435 If you do not set the terminal flags properly, some older terminals
436 will not work. This is because their commands may contain the
437 characters that normally signify newline, carriage return and
438 horizontal tab--characters which the kernel thinks it ought to modify
441 When you change the kernel's terminal flags, you must arrange to
442 restore them to their normal state when your program exits. This
443 implies that the program must catch fatal signals such as `SIGQUIT' and
444 `SIGINT' and restore the old terminal flags before actually terminating.
446 Modern terminals' commands do not use these special characters, so
447 if you do not care about problems with old terminals, you can leave the
448 kernel's terminal flags unaltered.
451 File: termcap.info, Node: Padding, Next: Parameters, Prev: Initialize, Up: Library
456 "Padding" means outputting null characters following a terminal
457 display command that takes a long time to execute. The terminal
458 description says which commands require padding and how much; the
459 function `tputs', described below, outputs a terminal command while
460 extracting from it the padding information, and then outputs the
461 padding that is necessary.
465 * Why Pad:: Explanation of padding.
466 * Not Enough:: When there is not enough padding.
467 * Describe Padding:: The data base says how much padding a terminal needs.
468 * Output Padding:: Using `tputs' to output the needed padding.
471 File: termcap.info, Node: Why Pad, Next: Not Enough, Up: Padding
476 Most types of terminal have commands that take longer to execute
477 than they do to send over a high-speed line. For example, clearing the
478 screen may take 20msec once the entire command is received. During
479 that time, on a 9600 bps line, the terminal could receive about 20
480 additional output characters while still busy clearing the screen.
481 Every terminal has a certain amount of buffering capacity to remember
482 output characters that cannot be processed yet, but too many slow
483 commands in a row can cause the buffer to fill up. Then any additional
484 output that cannot be processed immediately will be lost.
486 To avoid this problem, we normally follow each display command with
487 enough useless charaters (usually null characters) to fill up the time
488 that the display command needs to execute. This does the job if the
489 terminal throws away null characters without using up space in the
490 buffer (which most terminals do). If enough padding is used, no output
491 can ever be lost. The right amount of padding avoids loss of output
492 without slowing down operation, since the time used to transmit padding
493 is time that nothing else could be done.
495 The number of padding characters needed for an operation depends on
496 the line speed. In fact, it is proportional to the line speed. A 9600
497 baud line transmits about one character per msec, so the clear screen
498 command in the example above would need about 20 characters of padding.
499 At 1200 baud, however, only about 3 characters of padding are needed
503 File: termcap.info, Node: Not Enough, Next: Describe Padding, Prev: Why Pad, Up: Padding
505 When There Is Not Enough Padding
506 --------------------------------
508 There are several common manifestations of insufficient padding.
510 * Emacs displays `I-search: ^Q-' at the bottom of the screen.
512 This means that the terminal thought its buffer was getting full of
513 display commands, so it tried to tell the computer to stop sending
516 * The screen is garbled intermittently, or the details of garbling
517 vary when you repeat the action. (A garbled screen could be due
518 to a command which is simply incorrect, or to user option in the
519 terminal which doesn't match the assumptions of the terminal
520 description, but this usually leads to reproducible failure.)
522 This means that the buffer did get full, and some commands were
523 lost. Many changeable factors can change which ones are lost.
525 * Screen is garbled at high output speeds but not at low speeds.
526 Padding problems nearly always go away at low speeds, usually even
529 This means that a high enough speed permits commands to arrive
530 faster than they can be executed.
532 Although any obscure command on an obscure terminal might lack
533 padding, in practice problems arise most often from the clearing
534 commands `cl' and `cd' (*note Clearing::.), the scrolling commands `sf'
535 and `sr' (*note Scrolling::.), and the line insert/delete commands `al'
536 and `dl' (*note Insdel Line::.).
538 Occasionally the terminal description fails to define `sf' and some
539 programs will use `do' instead, so you may get a problem with `do'. If
540 so, first define `sf' just like `do', then add some padding to `sf'.
542 The best strategy is to add a lot of padding at first, perhaps 200
543 msec. This is much more than enough; in fact, it should cause a
544 visible slowdown. (If you don't see a slowdown, the change has not
545 taken effect; *note Changing::..) If this makes the problem go away,
546 you have found the right place to add padding; now reduce the amount
547 until the problem comes back, then increase it again. If the problem
548 remains, either it is in some other capability or it is not a matter of
551 Keep in mind that on many terminals the correct padding for
552 insert/delete line or for scrolling is cursor-position dependent. If
553 you get problems from scrolling a large region of the screen but not
554 from scrolling a small part (just a few lines moving), it may mean that
555 fixed padding should be replaced with position-dependent padding.
558 File: termcap.info, Node: Describe Padding, Next: Output Padding, Prev: Not Enough, Up: Padding
560 Specifying Padding in a Terminal Description
561 --------------------------------------------
563 In the terminal description, the amount of padding required by each
564 display command is recorded as a sequence of digits at the front of the
565 command. These digits specify the padding time in milliseconds (msec).
566 They can be followed optionally by a decimal point and one more digit,
567 which is a number of tenths of msec.
569 Sometimes the padding needed by a command depends on the cursor
570 position. For example, the time taken by an "insert line" command is
571 usually proportional to the number of lines that need to be moved down
572 or cleared. An asterisk (`*') following the padding time says that the
573 time should be multiplied by the number of screen lines affected by the
578 is used to describe the "insert line" command for a certain terminal.
579 The padding required is 1.3 msec per line affected. The command itself
582 The padding time specified in this way tells `tputs' how many pad
583 characters to output. *Note Output Padding::.
585 Two special capability values affect padding for all commands.
586 These are the `pc' and `pb'. The variable `pc' specifies the character
587 to pad with, and `pb' the speed below which no padding is needed. The
588 defaults for these variables, a null character and 0, are correct for
589 most terminals. *Note Pad Specs::.
592 File: termcap.info, Node: Output Padding, Prev: Describe Padding, Up: Padding
594 Performing Padding with `tputs'
595 -------------------------------
597 Use the termcap function `tputs' to output a string containing an
598 optional padding spec of the form described above (*note Describe
599 Padding::.). The function `tputs' strips off and decodes the padding
600 spec, outputs the rest of the string, and then outputs the appropriate
601 padding. Here is its declaration in ANSI C:
606 int tputs (char *STRING, int NLINES, int (*OUTFUN) ());
608 Here STRING is the string (including padding spec) to be output;
609 NLINES is the number of lines affected by the operation, which is used
610 to multiply the amount of padding if the padding spec ends with a `*'.
611 Finally, OUTFUN is a function (such as `fputchar') that is called to
612 output each character. When actually called, OUTFUN should expect one
613 argument, a character.
615 The operation of `tputs' is controlled by two global variables,
616 `ospeed' and `PC'. The value of `ospeed' is supposed to be the
617 terminal output speed, encoded as in the `ioctl' system call which gets
618 the speed information. This is needed to compute the number of padding
619 characters. The value of `PC' is the character used for padding.
621 You are responsible for storing suitable values into these variables
622 before using `tputs'. The value stored into the `PC' variable should be
623 taken from the `pc' capability in the terminal description (*note Pad
624 Specs::.). Store zero in `PC' if there is no `pc' capability.
626 The argument NLINES requires some thought. Normally, it should be
627 the number of lines whose contents will be cleared or moved by the
628 command. For cursor motion commands, or commands that do editing
629 within one line, use the value 1. For most commands that affect
630 multiple lines, such as `al' (insert a line) and `cd' (clear from the
631 cursor to the end of the screen), NLINES should be the screen height
632 minus the current vertical position (origin 0). For multiple insert
633 and scroll commands such as `AL' (insert multiple lines), that same
634 value for NLINES is correct; the number of lines being inserted is not
637 If a "scroll window" feature is used to reduce the number of lines
638 affected by a command, the value of NLINES should take this into
639 account. This is because the delay time required depends on how much
640 work the terminal has to do, and the scroll window feature reduces the
641 work. *Note Scrolling::.
643 Commands such as `ic' and `dc' (insert or delete characters) are
644 problematical because the padding needed by these commands is
645 proportional to the number of characters affected, which is the number
646 of columns from the cursor to the end of the line. It would be nice to
647 have a way to specify such a dependence, and there is no need for
648 dependence on vertical position in these commands, so it is an obvious
649 idea to say that for these commands NLINES should really be the number
650 of columns affected. However, the definition of termcap clearly says
651 that NLINES is always the number of lines affected, even in this case,
652 where it is always 1. It is not easy to change this rule now, because
653 too many programs and terminal descriptions have been written to follow
656 Because NLINES is always 1 for the `ic' and `dc' strings, there is
657 no reason for them to use `*', but some of them do. These should be
658 corrected by deleting the `*'. If, some day, such entries have
659 disappeared, it may be possible to change to a more useful convention
660 for the NLINES argument for these operations without breaking any
664 File: termcap.info, Node: Parameters, Prev: Padding, Up: Library
666 Filling In Parameters
667 =====================
669 Some terminal control strings require numeric "parameters". For
670 example, when you move the cursor, you need to say what horizontal and
671 vertical positions to move it to. The value of the terminal's `cm'
672 capability, which says how to move the cursor, cannot simply be a
673 string of characters; it must say how to express the cursor position
674 numbers and where to put them within the command.
676 The specifications of termcap include conventions as to which
677 string-valued capabilities require parameters, how many parameters, and
678 what the parameters mean; for example, it defines the `cm' string to
679 take two parameters, the vertical and horizontal positions, with 0,0
680 being the upper left corner. These conventions are described where the
681 individual commands are documented.
683 Termcap also defines a language used within the capability
684 definition for specifying how and where to encode the parameters for
685 output. This language uses character sequences starting with `%'.
686 (This is the same idea as `printf', but the details are different.)
687 The language for parameter encoding is described in this section.
689 A program that is doing display output calls the functions `tparam'
690 or `tgoto' to encode parameters according to the specifications. These
691 functions produce a string containing the actual commands to be output
692 (as well a padding spec which must be processed with `tputs'; *note
697 * Encode Parameters:: The language for encoding parameters.
698 * Using Parameters:: Outputting a string command with parameters.
701 File: termcap.info, Node: Encode Parameters, Next: Using Parameters, Up: Parameters
703 Describing the Encoding
704 -----------------------
706 A terminal command string that requires parameters contains special
707 character sequences starting with `%' to say how to encode the
708 parameters. These sequences control the actions of `tparam' and
711 The parameters values passed to `tparam' or `tgoto' are considered
712 to form a vector. A pointer into this vector determines the next
713 parameter to be processed. Some of the `%'-sequences encode one
714 parameter and advance the pointer to the next parameter. Other
715 `%'-sequences alter the pointer or alter the parameter values without
718 For example, the `cm' string for a standard ANSI terminal is written
719 as `\E[%i%d;%dH'. (`\E' stands for ESC.) `cm' by convention always
720 requires two parameters, the vertical and horizontal goal positions, so
721 this string specifies the encoding of two parameters. Here `%i'
722 increments the two values supplied, and each `%d' encodes one of the
723 values in decimal. If the cursor position values 20,58 are encoded
724 with this string, the result is `\E[21;59H'.
726 First, here are the `%'-sequences that generate output. Except for
727 `%%', each of them encodes one parameter and advances the pointer to
728 the following parameter.
731 Output a single `%'. This is the only way to represent a literal
732 `%' in a terminal command with parameters. `%%' does not use up a
736 As in `printf', output the next parameter in decimal.
739 Like `%02d' in `printf': output the next parameter in decimal, and
740 always use at least two digits.
743 Like `%03d' in `printf': output the next parameter in decimal, and
744 always use at least three digits. Note that `%4' and so on are
748 Output the next parameter as a single character whose ASCII code is
749 the parameter value. Like `%c' in `printf'.
752 Add the next parameter to the character CHAR, and output the
753 resulting character. For example, `%+ ' represents 0 as a space,
756 The following `%'-sequences specify alteration of the parameters
757 (their values, or their order) rather than encoding a parameter for
758 output. They generate no output; they are used only for their side
759 effects on the parameters. Also, they do not advance the "next
760 parameter" pointer except as explicitly stated. Only `%i', `%r' and
761 `%>' are defined in standard Unix termcap. The others are GNU
765 Increment the next two parameters. This is used for terminals that
766 expect cursor positions in origin 1. For example, `%i%d,%d' would
767 output two parameters with `1' for 0, `2' for 1, etc.
770 Interchange the next two parameters. This is used for terminals
771 whose cursor positioning command expects the horizontal position
775 Skip the next parameter. Do not output anything.
778 Back up one parameter. The last parameter used will become once
779 again the next parameter to be output, and the next output command
780 will use it. Using `%b' more than once, you can back up any
781 number of parameters, and you can refer to each parameter any
785 Conditionally increment the next parameter. Here C1 and C2 are
786 characters which stand for their ASCII codes as numbers. If the
787 next parameter is greater than the ASCII code of C1, the ASCII
788 code of C2 is added to it.
791 Perform arithmetic on the next parameter, do not use it up, and do
792 not output anything. Here OP specifies the arithmetic operation,
793 while TYPE and POS together specify the other operand.
795 Spaces are used above to separate the operands for clarity; the
796 spaces don't appear in the data base, where this sequence is
797 exactly five characters long.
799 The character OP says what kind of arithmetic operation to
800 perform. It can be any of these characters:
803 assign a value to the next parameter, ignoring its old value.
804 The new value comes from the other operand.
807 add the other operand to the next parameter.
810 subtract the other operand from the next parameter.
813 multiply the next parameter by the other operand.
816 divide the next parameter by the other operand.
818 The "other operand" may be another parameter's value or a constant;
819 the character TYPE says which. It can be:
822 Use another parameter. The character POS says which
823 parameter to use. Subtract 64 from its ASCII code to get the
824 position of the desired parameter relative to this one. Thus,
825 the character `A' as POS means the parameter after the next
826 one; the character `?' means the parameter before the next
830 Use a constant value. The character POS specifies the value
831 of the constant. The 0200 bit is cleared out, so that 0200
832 can be used to represent zero.
834 The following `%'-sequences are special purpose hacks to compensate
835 for the weird designs of obscure terminals. They modify the next
836 parameter or the next two parameters but do not generate output and do
837 not use up any parameters. `%m' is a GNU extension; the others are
838 defined in standard Unix termcap.
841 Exclusive-or the next parameter with 0140, and likewise the
842 parameter after next.
845 Complement all the bits of the next parameter and the parameter
849 Encode the next parameter in BCD. It alters the value of the
850 parameter by adding six times the quotient of the parameter by ten.
851 Here is a C statement that shows how the new value is computed:
853 PARM = (PARM / 10) * 16 + PARM % 10;
856 Transform the next parameter as needed by Delta Data terminals.
857 This involves subtracting twice the remainder of the parameter by
860 PARM -= 2 * (PARM % 16);
863 File: termcap.info, Node: Using Parameters, Prev: Encode Parameters, Up: Parameters
865 Sending Display Commands with Parameters
866 ----------------------------------------
868 The termcap library functions `tparam' and `tgoto' serve as the
869 analog of `printf' for terminal string parameters. The newer function
870 `tparam' is a GNU extension, more general but missing from Unix
871 termcap. The original parameter-encoding function is `tgoto', which is
872 preferable for cursor motion.
876 * tparam:: The general case, for GNU termcap only.
877 * tgoto:: The special case of cursor motion.
880 File: termcap.info, Node: tparam, Next: tgoto, Up: Using Parameters
885 The function `tparam' can encode display commands with any number of
886 parameters and allows you to specify the buffer space. It is the
887 preferred function for encoding parameters for all but the `cm'
888 capability. Its ANSI C declaration is as follows:
890 char *tparam (char *CTLSTRING, char *BUFFER, int SIZE, int PARM1,...)
892 The arguments are a control string CTLSTRING (the value of a terminal
893 capability, presumably), an output buffer BUFFER and SIZE, and any
894 number of integer parameters to be encoded. The effect of `tparam' is
895 to copy the control string into the buffer, encoding parameters
896 according to the `%' sequences in the control string.
898 You describe the output buffer by its address, BUFFER, and its size
899 in bytes, SIZE. If the buffer is not big enough for the data to be
900 stored in it, `tparam' calls `malloc' to get a larger buffer. In
901 either case, `tparam' returns the address of the buffer it ultimately
902 uses. If the value equals BUFFER, your original buffer was used.
903 Otherwise, a new buffer was allocated, and you must free it after you
904 are done with printing the results. If you pass zero for SIZE and
905 BUFFER, `tparam' always allocates the space with `malloc'.
907 All capabilities that require parameters also have the ability to
908 specify padding, so you should use `tputs' to output the string
909 produced by `tparam'. *Note Padding::. Here is an example.
915 buf = tparam (command, buffer, 40, parm);
916 tputs (buf, 1, fputchar);
921 If a parameter whose value is zero is encoded with `%.'-style
922 encoding, the result is a null character, which will confuse `tputs'.
923 This would be a serious problem, but luckily `%.' encoding is used only
924 by a few old models of terminal, and only for the `cm' capability. To
925 solve the problem, use `tgoto' rather than `tparam' to encode the `cm'
929 File: termcap.info, Node: tgoto, Prev: tparam, Up: Using Parameters
934 The special case of cursor motion is handled by `tgoto'. There are
935 two reasons why you might choose to use `tgoto':
937 * For Unix compatibility, because Unix termcap does not have
940 * For the `cm' capability, since `tgoto' has a special feature to
941 avoid problems with null characters, tabs and newlines on certain
942 old terminal types that use `%.' encoding for that capability.
944 Here is how `tgoto' might be declared in ANSI C:
946 char *tgoto (char *CSTRING, int HPOS, int VPOS)
948 There are three arguments, the terminal description's `cm' string and
949 the two cursor position numbers; `tgoto' computes the parametrized
950 string in an internal static buffer and returns the address of that
951 buffer. The next time you use `tgoto' the same buffer will be reused.
953 Parameters encoded with `%.' encoding can generate null characters,
954 tabs or newlines. These might cause trouble: the null character because
955 `tputs' would think that was the end of the string, the tab because the
956 kernel or other software might expand it into spaces, and the newline
957 becaue the kernel might add a carriage-return, or padding characters
958 normally used for a newline. To prevent such problems, `tgoto' is
959 careful to avoid these characters. Here is how this works: if the
960 target cursor position value is such as to cause a problem (that is to
961 say, zero, nine or ten), `tgoto' increments it by one, then compensates
962 by appending a string to move the cursor back or up one position.
964 The compensation strings to use for moving back or up are found in
965 global variables named `BC' and `UP'. These are actual external C
966 variables with upper case names; they are declared `char *'. It is up
967 to you to store suitable values in them, normally obtained from the
968 `le' and `up' terminal capabilities in the terminal description with
969 `tgetstr'. Alternatively, if these two variables are both zero, the
970 feature of avoiding nulls, tabs and newlines is turned off.
972 It is safe to use `tgoto' for commands other than `cm' only if you
973 have stored zero in `BC' and `UP'.
975 Note that `tgoto' reverses the order of its operands: the horizontal
976 position comes before the vertical position in the arguments to
977 `tgoto', even though the vertical position comes before the horizontal
978 in the parameters of the `cm' string. If you use `tgoto' with a
979 command such as `AL' that takes one parameter, you must pass the
980 parameter to `tgoto' as the "vertical position".
983 File: termcap.info, Node: Data Base, Next: Capabilities, Prev: Library, Up: Top
985 The Format of the Data Base
986 ***************************
988 The termcap data base of terminal descriptions is stored in the file
989 `/etc/termcap'. It contains terminal descriptions, blank lines, and
992 A terminal description starts with one or more names for the
993 terminal type. The information in the description is a series of
994 "capability names" and values. The capability names have standard
995 meanings (*note Capabilities::.) and their values describe the terminal.
999 * Format:: Overall format of a terminal description.
1000 * Capability Format:: Format of capabilities within a description.
1001 * Naming:: Naming conventions for terminal types.
1002 * Inheriting:: Inheriting part of a description from
1003 a related terminal type.
1004 * Changing:: When changes in the data base take effect.
1007 File: termcap.info, Node: Format, Next: Capability Format, Up: Data Base
1009 Terminal Description Format
1010 ===========================
1012 Aside from comments (lines starting with `#', which are ignored),
1013 each nonblank line in the termcap data base is a terminal description.
1014 A terminal description is nominally a single line, but it can be split
1015 into multiple lines by inserting the two characters `\ newline'. This
1016 sequence is ignored wherever it appears in a description.
1018 The preferred way to split the description is between capabilities:
1019 insert the four characters `: \ newline tab' immediately before any
1020 colon. This allows each sub-line to start with some indentation. This
1021 works because, after the `\ newline' are ignored, the result is `: tab
1022 :'; the first colon ends the preceding capability and the second colon
1023 starts the next capability. If you split with `\ newline' alone, you
1024 may not add any indentation after them.
1026 Here is a real example of a terminal description:
1029 :cr=^M:do=^J:nl=^J:bl=^G:\
1030 :le=^H:bs:cd=\EJ:ce=\EK:cl=\EH\EJ:\
1031 :cm=\EY%+ %+ :co#80:li#24:\
1032 :nd=\EC:ta=^I:pt:sr=\EI:up=\EA:\
1033 :ku=\EA:kd=\EB:kr=\EC:kl=\ED:kb=^H:
1035 Each terminal description begins with several names for the terminal
1036 type. The names are separated by `|' characters, and a colon ends the
1037 last name. The first name should be two characters long; it exists
1038 only for the sake of very old Unix systems and is never used in modern
1039 systems. The last name should be a fully verbose name such as "DEC
1040 vt52" or "Ann Arbor Ambassador with 48 lines". The other names should
1041 include whatever the user ought to be able to specify to get this
1042 terminal type, such as `vt52' or `aaa-48'. *Note Naming::, for
1043 information on how to choose terminal type names.
1045 After the terminal type names come the terminal capabilities,
1046 separated by colons and with a colon after the last one. Each
1047 capability has a two-letter name, such as `cm' for "cursor motion
1048 string" or `li' for "number of display lines".
1051 File: termcap.info, Node: Capability Format, Next: Naming, Prev: Format, Up: Data Base
1053 Writing the Capabilities
1054 ========================
1056 There are three kinds of capabilities: flags, numbers, and strings.
1057 Each kind has its own way of being written in the description. Each
1058 defined capability has by convention a particular kind of value; for
1059 example, `li' always has a numeric value and `cm' always a string value.
1061 A flag capability is thought of as having a boolean value: the value
1062 is true if the capability is present, false if not. When the
1063 capability is present, just write its name between two colons.
1065 A numeric capability has a value which is a nonnegative number.
1066 Write the capability name, a `#', and the number, between two colons.
1067 For example, `...:li#48:...' is how you specify the `li' capability for
1070 A string-valued capability has a value which is a sequence of
1071 characters. Usually these are the characters used to perform some
1072 display operation. Write the capability name, a `=', and the
1073 characters of the value, between two colons. For example,
1074 `...:cm=\E[%i%d;%dH:...' is how the cursor motion command for a
1075 standard ANSI terminal would be specified.
1077 Special characters in the string value can be expressed using
1078 `\'-escape sequences as in C; in addition, `\E' stands for ESC. `^' is
1079 also a kind of escape character; `^' followed by CHAR stands for the
1080 control-equivalent of CHAR. Thus, `^a' stands for the character
1081 control-a, just like `\001'. `\' and `^' themselves can be represented
1084 To include a colon in the string, you must write `\072'. You might
1085 ask, "Why can't `\:' be used to represent a colon?" The reason is that
1086 the interrogation functions do not count slashes while looking for a
1087 capability. Even if `:ce=ab\:cd:' were interpreted as giving the `ce'
1088 capability the value `ab:cd', it would also appear to define `cd' as a
1091 The string value will often contain digits at the front to specify
1092 padding (*note Padding::.) and/or `%'-sequences within to specify how
1093 to encode parameters (*note Parameters::.). Although these things are
1094 not to be output literally to the terminal, they are considered part of
1095 the value of the capability. They are special only when the string
1096 value is processed by `tputs', `tparam' or `tgoto'. By contrast, `\'
1097 and `^' are considered part of the syntax for specifying the characters
1100 Let's look at the VT52 example again:
1103 :cr=^M:do=^J:nl=^J:bl=^G:\
1104 :le=^H:bs:cd=\EJ:ce=\EK:cl=\EH\EJ:\
1105 :cm=\EY%+ %+ :co#80:li#24:\
1106 :nd=\EC:ta=^I:pt:sr=\EI:up=\EA:\
1107 :ku=\EA:kd=\EB:kr=\EC:kl=\ED:kb=^H:
1109 Here we see the numeric-valued capabilities `co' and `li', the flags
1110 `bs' and `pt', and many string-valued capabilities. Most of the
1111 strings start with ESC represented as `\E'. The rest contain control
1112 characters represented using `^'. The meanings of the individual
1113 capabilities are defined elsewhere (*note Capabilities::.).