1 A Hacker's Guide to NCURSES
6 * Objective of the Package
8 + How to Design Extensions
9 * Portability and Configuration
10 * Documentation Conventions
12 * A Tour of the Ncurses Library
17 + Output and Screen Updating
18 * The Forms and Menu Libraries
19 * A Tour of the Terminfo Compiler
20 + Translation of Non-use Capabilities
21 + Use Capability Resolution
22 + Source-Form Translation
24 * Style Tips for Developers
29 This document is a hacker's tour of the ncurses library and utilities.
30 It discusses design philosophy, implementation methods, and the
31 conventions used for coding and documentation. It is recommended
32 reading for anyone who is interested in porting, extending or
33 improving the package.
35 Objective of the Package
37 The objective of the ncurses package is to provide a free software API
38 for character-cell terminals and terminal emulators with the following
40 * Source-compatible with historical curses implementations
41 (including the original BSD curses and System V curses.
42 * Conformant with the XSI Curses standard issued as part of XPG4 by
44 * High-quality -- stable and reliable code, wide portability, good
45 packaging, superior documentation.
46 * Featureful -- should eliminate as much of the drudgery of C
47 interface programming as possible, freeing programmers to think at
48 a higher level of design.
50 These objectives are in priority order. So, for example, source
51 compatibility with older version must trump featurefulness -- we
52 cannot add features if it means breaking the portion of the API
53 corresponding to historical curses versions.
57 We used System V curses as a model, reverse-engineering their API, in
58 order to fulfill the first two objectives.
60 System V curses implementations can support BSD curses programs with
61 just a recompilation, so by capturing the System V API we also capture
64 More importantly for the future, the XSI Curses standard issued by
65 X/Open is explicitly and closely modeled on System V. So conformance
66 with System V took us most of the way to base-level XSI conformance.
68 How to Design Extensions
70 The third objective (standards conformance) requires that it be easy
71 to condition source code using ncurses so that the absence of
72 nonstandard extensions does not break the code.
74 Accordingly, we have a policy of associating with each nonstandard
75 extension a feature macro, so that ncurses client code can use this
76 macro to condition in or out the code that requires the ncurses
79 For example, there is a macro NCURSES_MOUSE_VERSION which XSI Curses
80 does not define, but which is defined in the ncurses library header.
81 You can use this to condition the calls to the mouse API calls.
83 Portability and Configuration
85 Code written for ncurses may assume an ANSI-standard C compiler and
86 POSIX-compatible OS interface. It may also assume the presence of a
87 System-V-compatible select(2) call.
89 We encourage (but do not require) developers to make the code friendly
90 to less-capable UNIX environments wherever possible.
92 We encourage developers to support OS-specific optimizations and
93 methods not available under POSIX/ANSI, provided only that:
94 * All such code is properly conditioned so the build process does
95 not attempt to compile it under a plain ANSI/POSIX environment.
96 * Adding such implementation methods does not introduce
97 incompatibilities in the ncurses API between platforms.
99 We use GNU autoconf(1) as a tool to deal with portability issues. The
100 right way to leverage an OS-specific feature is to modify the autoconf
101 specification files (configure.in and aclocal.m4) to set up a new
102 feature macro, which you then use to condition your code.
104 Documentation Conventions
106 There are three kinds of documentation associated with this package.
107 Each has a different preferred format:
108 * Package-internal files (README, INSTALL, TO-DO etc.)
110 * Everything else (i.e., narrative documentation).
112 Our conventions are simple:
113 1. Maintain package-internal files in plain text. The expected viewer
114 for them more(1) or an editor window; there is no point in
116 2. Mark up manual pages in the man macros. These have to be viewable
117 through traditional man(1) programs.
118 3. Write everything else in HTML.
120 When in doubt, HTMLize a master and use lynx(1) to generate plain
121 ASCII (as we do for the announcement document).
123 The reason for choosing HTML is that it is (a) well-adapted for
124 on-line browsing through viewers that are everywhere; (b) more easily
125 readable as plain text than most other mark-ups, if you do not have a
126 viewer; and (c) carries enough information that you can generate a
127 nice-looking printed version from it. Also, of course, it make
128 exporting things like the announcement document to WWW pretty trivial.
132 The reporting address for bugs is bug-ncurses@gnu.org. This is a
133 majordomo list; to join, write to bug-ncurses-request@gnu.org with a
134 message containing the line:
135 subscribe <name>@<host.domain>
137 The ncurses code is maintained by a small group of volunteers. While
138 we try our best to fix bugs promptly, we simply do not have a lot of
139 hours to spend on elementary hand-holding. We rely on intelligent
140 cooperation from our users. If you think you have found a bug in
141 ncurses, there are some steps you can take before contacting us that
142 will help get the bug fixed quickly.
144 In order to use our bug-fixing time efficiently, we put people who
145 show us they have taken these steps at the head of our queue. This
146 means that if you do not, you will probably end up at the tail end and
147 have to wait a while.
148 1. Develop a recipe to reproduce the bug.
149 Bugs we can reproduce are likely to be fixed very quickly, often
150 within days. The most effective single thing you can do to get a
151 quick fix is develop a way we can duplicate the bad behavior --
152 ideally, by giving us source for a small, portable test program
153 that breaks the library. (Even better is a keystroke recipe using
154 one of the test programs provided with the distribution.)
155 2. Try to reproduce the bug on a different terminal type.
156 In our experience, most of the behaviors people report as library
157 bugs are actually due to subtle problems in terminal descriptions.
158 This is especially likely to be true if you are using a
159 traditional asynchronous terminal or PC-based terminal emulator,
160 rather than xterm or a UNIX console entry.
161 It is therefore extremely helpful if you can tell us whether or
162 not your problem reproduces on other terminal types. Usually you
163 will have both a console type and xterm available; please tell us
164 whether or not your bug reproduces on both.
165 If you have xterm available, it is also good to collect xterm
166 reports for different window sizes. This is especially true if you
167 normally use an unusual xterm window size -- a surprising number
168 of the bugs we have seen are either triggered or masked by these.
169 3. Generate and examine a trace file for the broken behavior.
170 Recompile your program with the debugging versions of the
171 libraries. Insert a trace() call with the argument set to
172 TRACE_UPDATE. (See "Writing Programs with NCURSES" for details on
173 trace levels.) Reproduce your bug, then look at the trace file to
174 see what the library was actually doing.
175 Another frequent cause of apparent bugs is application coding
176 errors that cause the wrong things to be put on the virtual
177 screen. Looking at the virtual-screen dumps in the trace file will
178 tell you immediately if this is happening, and save you from the
179 possible embarrassment of being told that the bug is in your code
180 and is your problem rather than ours.
181 If the virtual-screen dumps look correct but the bug persists, it
182 is possible to crank up the trace level to give more and more
183 information about the library's update actions and the control
184 sequences it issues to perform them. The test directory of the
185 distribution contains a tool for digesting these logs to make them
186 less tedious to wade through.
187 Often you will find terminfo problems at this stage by noticing
188 that the escape sequences put out for various capabilities are
189 wrong. If not, you are likely to learn enough to be able to
190 characterize any bug in the screen-update logic quite exactly.
191 4. Report details and symptoms, not just interpretations.
192 If you do the preceding two steps, it is very likely that you will
193 discover the nature of the problem yourself and be able to send us
194 a fix. This will create happy feelings all around and earn you
195 good karma for the first time you run into a bug you really cannot
196 characterize and fix yourself.
197 If you are still stuck, at least you will know what to tell us.
198 Remember, we need details. If you guess about what is safe to
199 leave out, you are too likely to be wrong.
200 If your bug produces a bad update, include a trace file. Try to
201 make the trace at the least voluminous level that pins down the
202 bug. Logs that have been through tracemunch are OK, it does not
203 throw away any information (actually they are better than
204 un-munched ones because they are easier to read).
205 If your bug produces a core-dump, please include a symbolic stack
206 trace generated by gdb(1) or your local equivalent.
207 Tell us about every terminal on which you have reproduced the bug
208 -- and every terminal on which you cannot. Ideally, sent us
209 terminfo sources for all of these (yours might differ from ours).
210 Include your ncurses version and your OS/machine type, of course!
211 You can find your ncurses version in the curses.h file.
213 If your problem smells like a logic error or in cursor movement or
214 scrolling or a bad capability, there are a couple of tiny test frames
215 for the library algorithms in the progs directory that may help you
216 isolate it. These are not part of the normal build, but do have their
217 own make productions.
219 The most important of these is mvcur, a test frame for the
220 cursor-movement optimization code. With this program, you can see
221 directly what control sequences will be emitted for any given cursor
222 movement or scroll/insert/delete operations. If you think you have got
223 a bad capability identified, you can disable it and test again. The
224 program is command-driven and has on-line help.
226 If you think the vertical-scroll optimization is broken, or just want
227 to understand how it works better, build hashmap and read the header
228 comments of hardscroll.c and hashmap.c; then try it out. You can also
229 test the hardware-scrolling optimization separately with hardscroll.
231 A Tour of the Ncurses Library
235 Most of the library is superstructure -- fairly trivial convenience
236 interfaces to a small set of basic functions and data structures used
237 to manipulate the virtual screen (in particular, none of this code
238 does any I/O except through calls to more fundamental modules
239 described below). The files
241 lib_addch.c lib_bkgd.c lib_box.c lib_chgat.c lib_clear.c
242 lib_clearok.c lib_clrbot.c lib_clreol.c lib_colorset.c lib_data.c
243 lib_delch.c lib_delwin.c lib_echo.c lib_erase.c lib_gen.c
244 lib_getstr.c lib_hline.c lib_immedok.c lib_inchstr.c lib_insch.c
245 lib_insdel.c lib_insstr.c lib_instr.c lib_isendwin.c lib_keyname.c
246 lib_leaveok.c lib_move.c lib_mvwin.c lib_overlay.c lib_pad.c
247 lib_printw.c lib_redrawln.c lib_scanw.c lib_screen.c lib_scroll.c
248 lib_scrollok.c lib_scrreg.c lib_set_term.c lib_slk.c
249 lib_slkatr_set.c lib_slkatrof.c lib_slkatron.c lib_slkatrset.c
250 lib_slkattr.c lib_slkclear.c lib_slkcolor.c lib_slkinit.c
251 lib_slklab.c lib_slkrefr.c lib_slkset.c lib_slktouch.c lib_touch.c
252 lib_unctrl.c lib_vline.c lib_wattroff.c lib_wattron.c lib_window.c
254 are all in this category. They are very unlikely to need change,
255 barring bugs or some fundamental reorganization in the underlying data
258 These files are used only for debugging support:
260 lib_trace.c lib_traceatr.c lib_tracebits.c lib_tracechr.c
261 lib_tracedmp.c lib_tracemse.c trace_buf.c
263 It is rather unlikely you will ever need to change these, unless you
264 want to introduce a new debug trace level for some reason.
266 There is another group of files that do direct I/O via tputs(),
267 computations on the terminal capabilities, or queries to the OS
268 environment, but nevertheless have only fairly low complexity. These
271 lib_acs.c lib_beep.c lib_color.c lib_endwin.c lib_initscr.c
272 lib_longname.c lib_newterm.c lib_options.c lib_termcap.c lib_ti.c
273 lib_tparm.c lib_tputs.c lib_vidattr.c read_entry.c.
275 They are likely to need revision only if ncurses is being ported to an
276 environment without an underlying terminfo capability representation.
278 These files have serious hooks into the tty driver and signal
281 lib_kernel.c lib_baudrate.c lib_raw.c lib_tstp.c lib_twait.c
283 If you run into porting snafus moving the package to another UNIX, the
284 problem is likely to be in one of these files. The file lib_print.c
285 uses sleep(2) and also falls in this category.
287 Almost all of the real work is done in the files
289 hardscroll.c hashmap.c lib_addch.c lib_doupdate.c lib_getch.c
290 lib_mouse.c lib_mvcur.c lib_refresh.c lib_setup.c lib_vidattr.c
292 Most of the algorithmic complexity in the library lives in these
293 files. If there is a real bug in ncurses itself, it is probably here.
294 We will tour some of these files in detail below (see The Engine
297 Finally, there is a group of files that is actually most of the
298 terminfo compiler. The reason this code lives in the ncurses library
299 is to support fallback to /etc/termcap. These files include
301 alloc_entry.c captoinfo.c comp_captab.c comp_error.c comp_hash.c
302 comp_parse.c comp_scan.c parse_entry.c read_termcap.c write_entry.c
304 We will discuss these in the compiler tour.
310 All ncurses input funnels through the function wgetch(), defined in
311 lib_getch.c. This function is tricky; it has to poll for keyboard and
312 mouse events and do a running match of incoming input against the set
313 of defined special keys.
315 The central data structure in this module is a FIFO queue, used to
316 match multiple-character input sequences against special-key
317 capabilities; also to implement pushback via ungetch().
319 The wgetch() code distinguishes between function key sequences and the
320 same sequences typed manually by doing a timed wait after each input
321 character that could lead a function key sequence. If the entire
322 sequence takes less than 1 second, it is assumed to have been
323 generated by a function key press.
325 Hackers bruised by previous encounters with variant select(2) calls
326 may find the code in lib_twait.c interesting. It deals with the
327 problem that some BSD selects do not return a reliable time-left
328 value. The function timed_wait() effectively simulates a System V
333 If the mouse interface is active, wgetch() polls for mouse events each
334 call, before it goes to the keyboard for input. It is up to
335 lib_mouse.c how the polling is accomplished; it may vary for different
338 Under xterm, however, mouse event notifications come in via the
339 keyboard input stream. They are recognized by having the kmous
340 capability as a prefix. This is kind of klugey, but trying to wire in
341 recognition of a mouse key prefix without going through the
342 function-key machinery would be just too painful, and this turns out
343 to imply having the prefix somewhere in the function-key capabilities
344 at terminal-type initialization.
346 This kluge only works because kmous is not actually used by any
347 historic terminal type or curses implementation we know of. Best guess
348 is it is a relic of some forgotten experiment in-house at Bell Labs
349 that did not leave any traces in the publicly-distributed System V
350 terminfo files. If System V or XPG4 ever gets serious about using it
351 again, this kluge may have to change.
353 Here are some more details about mouse event handling:
355 The lib_mouse()code is logically split into a lower level that accepts
356 event reports in a device-dependent format and an upper level that
357 parses mouse gestures and filters events. The mediating data structure
358 is a circular queue of event structures.
360 Functionally, the lower level's job is to pick up primitive events and
361 put them on the circular queue. This can happen in one of two ways:
362 either (a) _nc_mouse_event() detects a series of incoming mouse
363 reports and queues them, or (b) code in lib_getch.c detects the kmous
364 prefix in the keyboard input stream and calls _nc_mouse_inline to
365 queue up a series of adjacent mouse reports.
367 In either case, _nc_mouse_parse() should be called after the series is
368 accepted to parse the digested mouse reports (low-level events) into a
369 gesture (a high-level or composite event).
371 Output and Screen Updating
373 With the single exception of character echoes during a wgetnstr() call
374 (which simulates cooked-mode line editing in an ncurses window), the
375 library normally does all its output at refresh time.
377 The main job is to go from the current state of the screen (as
378 represented in the curscr window structure) to the desired new state
379 (as represented in the newscr window structure), while doing as little
382 The brains of this operation are the modules hashmap.c, hardscroll.c
383 and lib_doupdate.c; the latter two use lib_mvcur.c. Essentially, what
384 happens looks like this:
386 The hashmap.c module tries to detect vertical motion changes between
387 the real and virtual screens. This information is represented by the
388 oldindex members in the newscr structure. These are modified by
389 vertical-motion and clear operations, and both are re-initialized
390 after each update. To this change-journalling information, the hashmap
391 code adds deductions made using a modified Heckel algorithm on hash
392 values generated from the line contents.
394 The hardscroll.c module computes an optimum set of scroll, insertion,
395 and deletion operations to make the indices match. It calls
396 _nc_mvcur_scrolln() in lib_mvcur.c to do those motions.
398 Then lib_doupdate.c goes to work. Its job is to do line-by-line
399 transformations of curscr lines to newscr lines. Its main tool is the
400 routine mvcur() in lib_mvcur.c. This routine does cursor-movement
401 optimization, attempting to get from given screen location A to given
402 location B in the fewest output characters possible.
404 If you want to work on screen optimizations, you should use the fact
405 that (in the trace-enabled version of the library) enabling the
406 TRACE_TIMES trace level causes a report to be emitted after each
407 screen update giving the elapsed time and a count of characters
408 emitted during the update. You can use this to tell when an update
409 optimization improves efficiency.
411 In the trace-enabled version of the library, it is also possible to
412 disable and re-enable various optimizations at runtime by tweaking the
413 variable _nc_optimize_enable. See the file include/curses.h.in for
414 mask values, near the end.
416 The Forms and Menu Libraries
418 The forms and menu libraries should work reliably in any environment
419 you can port ncurses to. The only portability issue anywhere in them
420 is what flavor of regular expressions the built-in form field type
421 TYPE_REGEXP will recognize.
423 The configuration code prefers the POSIX regex facility, modeled on
424 System V's, but will settle for BSD regexps if the former is not
427 Historical note: the panels code was written primarily to assist in
428 porting u386mon 2.0 (comp.sources.misc v14i001-4) to systems lacking
429 panels support; u386mon 2.10 and beyond use it. This version has been
430 slightly cleaned up for ncurses.
432 A Tour of the Terminfo Compiler
434 The ncurses implementation of tic is rather complex internally; it has
435 to do a trying combination of missions. This starts with the fact
436 that, in addition to its normal duty of compiling terminfo sources
437 into loadable terminfo binaries, it has to be able to handle termcap
438 syntax and compile that too into terminfo entries.
440 The implementation therefore starts with a table-driven, dual-mode
441 lexical analyzer (in comp_scan.c). The lexer chooses its mode (termcap
442 or terminfo) based on the first "," or ":" it finds in each entry. The
443 lexer does all the work of recognizing capability names and values;
444 the grammar above it is trivial, just "parse entries till you run out
447 Translation of Non-use Capabilities
449 Translation of most things besides use capabilities is pretty
450 straightforward. The lexical analyzer's tokenizer hands each
451 capability name to a hash function, which drives a table lookup. The
452 table entry yields an index which is used to look up the token type in
453 another table, and controls interpretation of the value.
455 One possibly interesting aspect of the implementation is the way the
456 compiler tables are initialized. All the tables are generated by
457 various awk/sed/sh scripts from a master table include/Caps; these
458 scripts actually write C initializers which are linked to the
459 compiler. Furthermore, the hash table is generated in the same way, so
460 it doesn't have to be generated at compiler startup time (another
461 benefit of this organization is that the hash table can be in
462 shareable text space).
464 Thus, adding a new capability is usually pretty trivial, just a matter
465 of adding one line to the include/Caps file. We will have more to say
466 about this in the section on Source-Form Translation.
468 Use Capability Resolution
470 The background problem that makes tic tricky is not the capability
471 translation itself, it is the resolution of use capabilities. Older
472 versions would not handle forward use references for this reason (that
473 is, a using terminal always had to follow its use target in the source
474 file). By doing this, they got away with a simple implementation
475 tactic; compile everything as it blows by, then resolve uses from
478 This will not do for ncurses. The problem is that that the whole
479 compilation process has to be embeddable in the ncurses library so
480 that it can be called by the startup code to translate termcap entries
481 on the fly. The embedded version cannot go promiscuously writing
482 everything it translates out to disk -- for one thing, it will
483 typically be running with non-root permissions.
485 So our tic is designed to parse an entire terminfo file into a
486 doubly-linked circular list of entry structures in-core, and then do
487 use resolution in-memory before writing everything out. This design
488 has other advantages: it makes forward and back use-references equally
489 easy (so we get the latter for free), and it makes checking for name
490 collisions before they are written out easy to do.
492 And this is exactly how the embedded version works. But the
493 stand-alone user-accessible version of tic partly reverts to the
494 historical strategy; it writes to disk (not keeping in core) any entry
495 with no use references.
497 This is strictly a core-economy kluge, implemented because the
498 terminfo master file is large enough that some core-poor systems swap
499 like crazy when you compile it all in memory...there have been reports
500 of this process taking three hours, rather than the twenty seconds or
501 less typical on the author's development box.
503 So. The executable tic passes the entry-parser a hook that immediately
504 writes out the referenced entry if it has no use capabilities. The
505 compiler main loop refrains from adding the entry to the in-core list
506 when this hook fires. If some other entry later needs to reference an
507 entry that got written immediately, that is OK; the resolution code
508 will fetch it off disk when it cannot find it in core.
510 Name collisions will still be detected, just not as cleanly. The
511 write_entry() code complains before overwriting an entry that
512 postdates the time of tic's first call to write_entry(), Thus it will
513 complain about overwriting entries newly made during the tic run, but
514 not about overwriting ones that predate it.
516 Source-Form Translation
518 Another use of tic is to do source translation between various termcap
519 and terminfo formats. There are more variants out there than you might
520 think; the ones we know about are described in the captoinfo(1) manual
523 The translation output code (dump_entry() in ncurses/dump_entry.c) is
524 shared with the infocmp(1) utility. It takes the same internal
525 representation used to generate the binary form and dumps it to
526 standard output in a specified format.
528 The include/Caps file has a header comment describing ways you can
529 specify source translations for nonstandard capabilities just by
530 altering the master table. It is possible to set up capability
531 aliasing or tell the compiler to plain ignore a given capability
532 without writing any C code at all.
534 For circumstances where you need to do algorithmic translation, there
535 are functions in parse_entry.c called after the parse of each entry
536 that are specifically intended to encapsulate such translations. This,
537 for example, is where the AIX box1 capability get translated to an
542 The infocmp utility is just a wrapper around the same entry-dumping
543 code used by tic for source translation. Perhaps the one interesting
544 aspect of the code is the use of a predicate function passed in to
545 dump_entry() to control which capabilities are dumped. This is
546 necessary in order to handle both the ordinary De-compilation case and
547 entry difference reporting.
549 The tput and clear utilities just do an entry load followed by a
550 tputs() of a selected capability.
552 Style Tips for Developers
554 See the TO-DO file in the top-level directory of the source
555 distribution for additions that would be particularly useful.
557 The prefix _nc_ should be used on library public functions that are
558 not part of the curses API in order to prevent pollution of the
559 application namespace. If you have to add to or modify the function
560 prototypes in curses.h.in, read ncurses/MKlib_gen.sh first so you can
561 avoid breaking XSI conformance. Please join the ncurses mailing list.
562 See the INSTALL file in the top level of the distribution for details
565 Look for the string FIXME in source files to tag minor bugs and
566 potential problems that could use fixing.
568 Do not try to auto-detect OS features in the main body of the C code.
569 That is the job of the configuration system.
571 To hold down complexity, do make your code data-driven. Especially, if
572 you can drive logic from a table filtered out of include/Caps, do it.
573 If you find you need to augment the data in that file in order to
574 generate the proper table, that is still preferable to ad-hoc code --
575 that is why the fifth field (flags) is there.
581 The following notes are intended to be a first step towards DOS and
582 Macintosh ports of the ncurses libraries.
584 The following library modules are "pure curses"; they operate only on
585 the curses internal structures, do all output through other curses
586 calls (not including tputs() and putp()) and do not call any other
587 UNIX routines such as signal(2) or the stdio library. Thus, they
588 should not need to be modified for single-terminal ports.
590 lib_addch.c lib_addstr.c lib_bkgd.c lib_box.c lib_clear.c
591 lib_clrbot.c lib_clreol.c lib_delch.c lib_delwin.c lib_erase.c
592 lib_inchstr.c lib_insch.c lib_insdel.c lib_insstr.c lib_keyname.c
593 lib_move.c lib_mvwin.c lib_newwin.c lib_overlay.c lib_pad.c
594 lib_printw.c lib_refresh.c lib_scanw.c lib_scroll.c lib_scrreg.c
595 lib_set_term.c lib_touch.c lib_tparm.c lib_tputs.c lib_unctrl.c
598 This module is pure curses, but calls outstr():
602 These modules are pure curses, except that they use tputs() and
605 lib_beep.c lib_color.c lib_endwin.c lib_options.c lib_slk.c
608 This modules assist in POSIX emulation on non-POSIX systems:
613 The following source files will not be needed for a
614 single-terminal-type port.
616 alloc_entry.c captoinfo.c clear.c comp_captab.c comp_error.c
617 comp_hash.c comp_main.c comp_parse.c comp_scan.c dump_entry.c
618 infocmp.c parse_entry.c read_entry.c tput.c write_entry.c
620 The following modules will use open()/read()/write()/close()/lseek()
621 on files, but no other OS calls.
624 used to read/write screen dumps
627 used to write trace data to the logfile
629 Modules that would have to be modified for a port start here:
631 The following modules are "pure curses" but contain assumptions
632 inappropriate for a memory-mapped port.
635 assumes there may be multiple terminals
638 assumes acs_map as a double indirection
641 assumes cursor moves have variable cost
644 assumes there may be multiple terminals
647 assumes there may be multiple terminals
649 The following modules use UNIX-specific calls:
663 various tty-manipulation and system calls
666 various tty-manipulation calls
669 various tty-manipulation calls
672 various tty-manipulation calls
675 signal-manipulation calls
678 gettimeofday(), select().
679 _________________________________________________________________
682 Eric S. Raymond <esr@snark.thyrsus.com>
684 (Note: This is not the bug address!)
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