1 \input texinfo @c -*-texinfo-*-
3 @setfilename standards.info
4 @settitle GNU Coding Standards
5 @c This date is automagically updated when you save this file:
6 @set lastupdate October 31, 2008
9 @dircategory GNU organization
11 * Standards: (standards). GNU coding standards.
14 @c @setchapternewpage odd
15 @setchapternewpage off
17 @c Put everything in one index (arbitrarily chosen to be the concept index).
23 @c This is used by a cross ref in make-stds.texi
27 The GNU coding standards, last updated @value{lastupdate}.
29 Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
30 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software
33 Permission is granted to copy, distribute and/or modify this document
34 under the terms of the GNU Free Documentation License, Version 1.2
35 or any later version published by the Free Software Foundation;
36 with no Invariant Sections, with no
37 Front-Cover Texts, and with no Back-Cover Texts.
38 A copy of the license is included in the section entitled ``GNU
39 Free Documentation License''.
43 @title GNU Coding Standards
44 @author Richard Stallman, et al.
45 @author last updated @value{lastupdate}
47 @vskip 0pt plus 1filll
54 @node Top, Preface, (dir), (dir)
61 * Preface:: About the GNU Coding Standards.
62 * Legal Issues:: Keeping free software free.
63 * Design Advice:: General program design.
64 * Program Behavior:: Program behavior for all programs
65 * Writing C:: Making the best use of C.
66 * Documentation:: Documenting programs.
67 * Managing Releases:: The release process.
68 * References:: Mentioning non-free software or documentation.
69 * GNU Free Documentation License:: Copying and sharing this manual.
75 @chapter About the GNU Coding Standards
77 The GNU Coding Standards were written by Richard Stallman and other GNU
78 Project volunteers. Their purpose is to make the GNU system clean,
79 consistent, and easy to install. This document can also be read as a
80 guide to writing portable, robust and reliable programs. It focuses on
81 programs written in C, but many of the rules and principles are useful
82 even if you write in another programming language. The rules often
83 state reasons for writing in a certain way.
85 This release of the GNU Coding Standards was last updated
88 @cindex where to obtain @code{standards.texi}
89 @cindex downloading this manual
90 If you did not obtain this file directly from the GNU project and
91 recently, please check for a newer version. You can get the GNU
92 Coding Standards from the GNU web server in many
93 different formats, including the Texinfo source, PDF, HTML, DVI, plain
94 text, and more, at: @uref{http://www.gnu.org/prep/standards/}.
96 Corrections or suggestions for this document should be sent to
97 @email{bug-standards@@gnu.org}. If you make a suggestion, please include a
98 suggested new wording for it; our time is limited. We prefer a context
99 diff to the @file{standards.texi} or @file{make-stds.texi} files, but if
100 you don't have those files, please mail your suggestion anyway.
102 These standards cover the minimum of what is important when writing a
103 GNU package. Likely, the need for additional standards will come up.
104 Sometimes, you might suggest that such standards be added to this
105 document. If you think your standards would be generally useful, please
108 You should also set standards for your package on many questions not
109 addressed or not firmly specified here. The most important point is to
110 be self-consistent---try to stick to the conventions you pick, and try
111 to document them as much as possible. That way, your program will be
112 more maintainable by others.
114 The GNU Hello program serves as an example of how to follow the GNU
115 coding standards for a trivial program.
116 @uref{http://www.gnu.org/software/hello/hello.html}.
119 @chapter Keeping Free Software Free
120 @cindex legal aspects
122 This chapter discusses how you can make sure that GNU software
123 avoids legal difficulties, and other related issues.
126 * Reading Non-Free Code:: Referring to proprietary programs.
127 * Contributions:: Accepting contributions.
128 * Trademarks:: How we deal with trademark issues.
131 @node Reading Non-Free Code
132 @section Referring to Proprietary Programs
133 @cindex proprietary programs
134 @cindex avoiding proprietary code
136 Don't in any circumstances refer to Unix source code for or during
137 your work on GNU! (Or to any other proprietary programs.)
139 If you have a vague recollection of the internals of a Unix program,
140 this does not absolutely mean you can't write an imitation of it, but
141 do try to organize the imitation internally along different lines,
142 because this is likely to make the details of the Unix version
143 irrelevant and dissimilar to your results.
145 For example, Unix utilities were generally optimized to minimize
146 memory use; if you go for speed instead, your program will be very
147 different. You could keep the entire input file in memory and scan it
148 there instead of using stdio. Use a smarter algorithm discovered more
149 recently than the Unix program. Eliminate use of temporary files. Do
150 it in one pass instead of two (we did this in the assembler).
152 Or, on the contrary, emphasize simplicity instead of speed. For some
153 applications, the speed of today's computers makes simpler algorithms
156 Or go for generality. For example, Unix programs often have static
157 tables or fixed-size strings, which make for arbitrary limits; use
158 dynamic allocation instead. Make sure your program handles NULs and
159 other funny characters in the input files. Add a programming language
160 for extensibility and write part of the program in that language.
162 Or turn some parts of the program into independently usable libraries.
163 Or use a simple garbage collector instead of tracking precisely when
164 to free memory, or use a new GNU facility such as obstacks.
167 @section Accepting Contributions
169 @cindex accepting contributions
171 If the program you are working on is copyrighted by the Free Software
172 Foundation, then when someone else sends you a piece of code to add to
173 the program, we need legal papers to use it---just as we asked you to
174 sign papers initially. @emph{Each} person who makes a nontrivial
175 contribution to a program must sign some sort of legal papers in order
176 for us to have clear title to the program; the main author alone is not
179 So, before adding in any contributions from other people, please tell
180 us, so we can arrange to get the papers. Then wait until we tell you
181 that we have received the signed papers, before you actually use the
184 This applies both before you release the program and afterward. If
185 you receive diffs to fix a bug, and they make significant changes, we
186 need legal papers for that change.
188 This also applies to comments and documentation files. For copyright
189 law, comments and code are just text. Copyright applies to all kinds of
190 text, so we need legal papers for all kinds.
192 We know it is frustrating to ask for legal papers; it's frustrating for
193 us as well. But if you don't wait, you are going out on a limb---for
194 example, what if the contributor's employer won't sign a disclaimer?
195 You might have to take that code out again!
197 You don't need papers for changes of a few lines here or there, since
198 they are not significant for copyright purposes. Also, you don't need
199 papers if all you get from the suggestion is some ideas, not actual code
200 which you use. For example, if someone sent you one implementation, but
201 you write a different implementation of the same idea, you don't need to
204 The very worst thing is if you forget to tell us about the other
205 contributor. We could be very embarrassed in court some day as a
208 We have more detailed advice for maintainers of programs; if you have
209 reached the stage of actually maintaining a program for GNU (whether
210 released or not), please ask us for a copy. It is also available
211 online for your perusal: @uref{http://www.gnu.org/prep/maintain/}.
217 Please do not include any trademark acknowledgements in GNU software
218 packages or documentation.
220 Trademark acknowledgements are the statements that such-and-such is a
221 trademark of so-and-so. The GNU Project has no objection to the basic
222 idea of trademarks, but these acknowledgements feel like kowtowing,
223 and there is no legal requirement for them, so we don't use them.
225 What is legally required, as regards other people's trademarks, is to
226 avoid using them in ways which a reader might reasonably understand as
227 naming or labeling our own programs or activities. For example, since
228 ``Objective C'' is (or at least was) a trademark, we made sure to say
229 that we provide a ``compiler for the Objective C language'' rather
230 than an ``Objective C compiler''. The latter would have been meant as
231 a shorter way of saying the former, but it does not explicitly state
232 the relationship, so it could be misinterpreted as using ``Objective
233 C'' as a label for the compiler rather than for the language.
235 Please don't use ``win'' as an abbreviation for Microsoft Windows in
236 GNU software or documentation. In hacker terminology, calling
237 something a ``win'' is a form of praise. If you wish to praise
238 Microsoft Windows when speaking on your own, by all means do so, but
239 not in GNU software. Usually we write the name ``Windows'' in full,
240 but when brevity is very important (as in file names and sometimes
241 symbol names), we abbreviate it to ``w''. For instance, the files and
242 functions in Emacs that deal with Windows start with @samp{w32}.
245 @chapter General Program Design
246 @cindex program design
248 This chapter discusses some of the issues you should take into
249 account when designing your program.
251 @c Standard or ANSI C
253 @c In 1989 the American National Standards Institute (ANSI) standardized
254 @c C as standard X3.159-1989. In December of that year the
255 @c International Standards Organization ISO adopted the ANSI C standard
256 @c making minor changes. In 1990 ANSI then re-adopted ISO standard
257 @c C. This version of C is known as either ANSI C or Standard C.
259 @c A major revision of the C Standard appeared in 1999.
262 * Source Language:: Which languages to use.
263 * Compatibility:: Compatibility with other implementations.
264 * Using Extensions:: Using non-standard features.
265 * Standard C:: Using standard C features.
266 * Conditional Compilation:: Compiling code only if a conditional is true.
269 @node Source Language
270 @section Which Languages to Use
271 @cindex programming languages
273 When you want to use a language that gets compiled and runs at high
274 speed, the best language to use is C. Using another language is like
275 using a non-standard feature: it will cause trouble for users. Even if
276 GCC supports the other language, users may find it inconvenient to have
277 to install the compiler for that other language in order to build your
278 program. For example, if you write your program in C++, people will
279 have to install the GNU C++ compiler in order to compile your program.
281 C has one other advantage over C++ and other compiled languages: more
282 people know C, so more people will find it easy to read and modify the
283 program if it is written in C.
285 So in general it is much better to use C, rather than the
286 comparable alternatives.
288 But there are two exceptions to that conclusion:
292 It is no problem to use another language to write a tool specifically
293 intended for use with that language. That is because the only people
294 who want to build the tool will be those who have installed the other
298 If an application is of interest only to a narrow part of the community,
299 then the question of which language it is written in has less effect on
300 other people, so you may as well please yourself.
303 Many programs are designed to be extensible: they include an interpreter
304 for a language that is higher level than C. Often much of the program
305 is written in that language, too. The Emacs editor pioneered this
309 @cindex GNOME and Guile
310 The standard extensibility interpreter for GNU software is Guile
311 (@uref{http://www.gnu.org/@/software/@/guile/}), which implements the
312 language Scheme (an especially clean and simple dialect of Lisp).
313 Guile also includes bindings for GTK+/GNOME, making it practical to
314 write modern GUI functionality within Guile. We don't reject programs
315 written in other ``scripting languages'' such as Perl and Python, but
316 using Guile is very important for the overall consistency of the GNU
321 @section Compatibility with Other Implementations
322 @cindex compatibility with C and @sc{posix} standards
323 @cindex @sc{posix} compatibility
325 With occasional exceptions, utility programs and libraries for GNU
326 should be upward compatible with those in Berkeley Unix, and upward
327 compatible with Standard C if Standard C specifies their
328 behavior, and upward compatible with @sc{posix} if @sc{posix} specifies
331 When these standards conflict, it is useful to offer compatibility
332 modes for each of them.
334 @cindex options for compatibility
335 Standard C and @sc{posix} prohibit many kinds of extensions. Feel
336 free to make the extensions anyway, and include a @samp{--ansi},
337 @samp{--posix}, or @samp{--compatible} option to turn them off.
338 However, if the extension has a significant chance of breaking any real
339 programs or scripts, then it is not really upward compatible. So you
340 should try to redesign its interface to make it upward compatible.
342 @cindex @code{POSIXLY_CORRECT}, environment variable
343 Many GNU programs suppress extensions that conflict with @sc{posix} if the
344 environment variable @code{POSIXLY_CORRECT} is defined (even if it is
345 defined with a null value). Please make your program recognize this
346 variable if appropriate.
348 When a feature is used only by users (not by programs or command
349 files), and it is done poorly in Unix, feel free to replace it
350 completely with something totally different and better. (For example,
351 @code{vi} is replaced with Emacs.) But it is nice to offer a compatible
352 feature as well. (There is a free @code{vi} clone, so we offer it.)
354 Additional useful features are welcome regardless of whether
355 there is any precedent for them.
357 @node Using Extensions
358 @section Using Non-standard Features
359 @cindex non-standard extensions
361 Many GNU facilities that already exist support a number of convenient
362 extensions over the comparable Unix facilities. Whether to use these
363 extensions in implementing your program is a difficult question.
365 On the one hand, using the extensions can make a cleaner program.
366 On the other hand, people will not be able to build the program
367 unless the other GNU tools are available. This might cause the
368 program to work on fewer kinds of machines.
370 With some extensions, it might be easy to provide both alternatives.
371 For example, you can define functions with a ``keyword'' @code{INLINE}
372 and define that as a macro to expand into either @code{inline} or
373 nothing, depending on the compiler.
375 In general, perhaps it is best not to use the extensions if you can
376 straightforwardly do without them, but to use the extensions if they
377 are a big improvement.
379 An exception to this rule are the large, established programs (such as
380 Emacs) which run on a great variety of systems. Using GNU extensions in
381 such programs would make many users unhappy, so we don't do that.
383 Another exception is for programs that are used as part of compilation:
384 anything that must be compiled with other compilers in order to
385 bootstrap the GNU compilation facilities. If these require the GNU
386 compiler, then no one can compile them without having them installed
387 already. That would be extremely troublesome in certain cases.
390 @section Standard C and Pre-Standard C
391 @cindex @sc{ansi} C standard
393 1989 Standard C is widespread enough now that it is ok to use its
394 features in new programs. There is one exception: do not ever use the
395 ``trigraph'' feature of Standard C.
397 1999 Standard C is not widespread yet, so please do not require its
398 features in programs. It is ok to use its features if they are present.
400 However, it is easy to support pre-standard compilers in most programs,
401 so if you know how to do that, feel free. If a program you are
402 maintaining has such support, you should try to keep it working.
404 @cindex function prototypes
405 To support pre-standard C, instead of writing function definitions in
406 standard prototype form,
415 write the definition in pre-standard style like this,
425 and use a separate declaration to specify the argument prototype:
431 You need such a declaration anyway, in a header file, to get the benefit
432 of prototypes in all the files where the function is called. And once
433 you have the declaration, you normally lose nothing by writing the
434 function definition in the pre-standard style.
436 This technique does not work for integer types narrower than @code{int}.
437 If you think of an argument as being of a type narrower than @code{int},
438 declare it as @code{int} instead.
440 There are a few special cases where this technique is hard to use. For
441 example, if a function argument needs to hold the system type
442 @code{dev_t}, you run into trouble, because @code{dev_t} is shorter than
443 @code{int} on some machines; but you cannot use @code{int} instead,
444 because @code{dev_t} is wider than @code{int} on some machines. There
445 is no type you can safely use on all machines in a non-standard
446 definition. The only way to support non-standard C and pass such an
447 argument is to check the width of @code{dev_t} using Autoconf and choose
448 the argument type accordingly. This may not be worth the trouble.
450 In order to support pre-standard compilers that do not recognize
451 prototypes, you may want to use a preprocessor macro like this:
454 /* Declare the prototype for a general external function. */
455 #if defined (__STDC__) || defined (WINDOWSNT)
456 #define P_(proto) proto
462 @node Conditional Compilation
463 @section Conditional Compilation
465 When supporting configuration options already known when building your
466 program we prefer using @code{if (... )} over conditional compilation,
467 as in the former case the compiler is able to perform more extensive
468 checking of all possible code paths.
470 For example, please write
490 A modern compiler such as GCC will generate exactly the same code in
491 both cases, and we have been using similar techniques with good success
492 in several projects. Of course, the former method assumes that
493 @code{HAS_FOO} is defined as either 0 or 1.
495 While this is not a silver bullet solving all portability problems,
496 and is not always appropriate, following this policy would have saved
497 GCC developers many hours, or even days, per year.
499 In the case of function-like macros like @code{REVERSIBLE_CC_MODE} in
500 GCC which cannot be simply used in @code{if( ...)} statements, there is
501 an easy workaround. Simply introduce another macro
502 @code{HAS_REVERSIBLE_CC_MODE} as in the following example:
505 #ifdef REVERSIBLE_CC_MODE
506 #define HAS_REVERSIBLE_CC_MODE 1
508 #define HAS_REVERSIBLE_CC_MODE 0
512 @node Program Behavior
513 @chapter Program Behavior for All Programs
515 This chapter describes conventions for writing robust
516 software. It also describes general standards for error messages, the
517 command line interface, and how libraries should behave.
520 * Non-GNU Standards:: We consider standards such as POSIX;
521 we don't "obey" them.
522 * Semantics:: Writing robust programs.
523 * Libraries:: Library behavior.
524 * Errors:: Formatting error messages.
525 * User Interfaces:: Standards about interfaces generally.
526 * Graphical Interfaces:: Standards for graphical interfaces.
527 * Command-Line Interfaces:: Standards for command line interfaces.
528 * Option Table:: Table of long options.
529 * OID Allocations:: Table of OID slots for GNU.
530 * Memory Usage:: When and how to care about memory needs.
531 * File Usage:: Which files to use, and where.
534 @node Non-GNU Standards
535 @section Non-GNU Standards
537 The GNU Project regards standards published by other organizations as
538 suggestions, not orders. We consider those standards, but we do not
539 ``obey'' them. In developing a GNU program, you should implement
540 an outside standard's specifications when that makes the GNU system
541 better overall in an objective sense. When it doesn't, you shouldn't.
543 In most cases, following published standards is convenient for
544 users---it means that their programs or scripts will work more
545 portably. For instance, GCC implements nearly all the features of
546 Standard C as specified by that standard. C program developers would
547 be unhappy if it did not. And GNU utilities mostly follow
548 specifications of POSIX.2; shell script writers and users would be
549 unhappy if our programs were incompatible.
551 But we do not follow either of these specifications rigidly, and there
552 are specific points on which we decided not to follow them, so as to
553 make the GNU system better for users.
555 For instance, Standard C says that nearly all extensions to C are
556 prohibited. How silly! GCC implements many extensions, some of which
557 were later adopted as part of the standard. If you want these
558 constructs to give an error message as ``required'' by the standard,
559 you must specify @samp{--pedantic}, which was implemented only so that
560 we can say ``GCC is a 100% implementation of the standard,'' not
561 because there is any reason to actually use it.
563 POSIX.2 specifies that @samp{df} and @samp{du} must output sizes by
564 default in units of 512 bytes. What users want is units of 1k, so
565 that is what we do by default. If you want the ridiculous behavior
566 ``required'' by POSIX, you must set the environment variable
567 @samp{POSIXLY_CORRECT} (which was originally going to be named
568 @samp{POSIX_ME_HARDER}).
570 GNU utilities also depart from the letter of the POSIX.2 specification
571 when they support long-named command-line options, and intermixing
572 options with ordinary arguments. This minor incompatibility with
573 POSIX is never a problem in practice, and it is very useful.
575 In particular, don't reject a new feature, or remove an old one,
576 merely because a standard says it is ``forbidden'' or ``deprecated.''
579 @section Writing Robust Programs
581 @cindex arbitrary limits on data
582 Avoid arbitrary limits on the length or number of @emph{any} data
583 structure, including file names, lines, files, and symbols, by allocating
584 all data structures dynamically. In most Unix utilities, ``long lines
585 are silently truncated''. This is not acceptable in a GNU utility.
587 @cindex @code{NUL} characters
588 Utilities reading files should not drop NUL characters, or any other
589 nonprinting characters @emph{including those with codes above 0177}.
590 The only sensible exceptions would be utilities specifically intended
591 for interface to certain types of terminals or printers
592 that can't handle those characters.
593 Whenever possible, try to make programs work properly with
594 sequences of bytes that represent multibyte characters, using encodings
595 such as UTF-8 and others.
597 @cindex error messages
598 Check every system call for an error return, unless you know you wish to
599 ignore errors. Include the system error text (from @code{perror} or
600 equivalent) in @emph{every} error message resulting from a failing
601 system call, as well as the name of the file if any and the name of the
602 utility. Just ``cannot open foo.c'' or ``stat failed'' is not
605 @cindex @code{malloc} return value
606 @cindex memory allocation failure
607 Check every call to @code{malloc} or @code{realloc} to see if it
608 returned zero. Check @code{realloc} even if you are making the block
609 smaller; in a system that rounds block sizes to a power of 2,
610 @code{realloc} may get a different block if you ask for less space.
612 In Unix, @code{realloc} can destroy the storage block if it returns
613 zero. GNU @code{realloc} does not have this bug: if it fails, the
614 original block is unchanged. Feel free to assume the bug is fixed. If
615 you wish to run your program on Unix, and wish to avoid lossage in this
616 case, you can use the GNU @code{malloc}.
618 You must expect @code{free} to alter the contents of the block that was
619 freed. Anything you want to fetch from the block, you must fetch before
622 If @code{malloc} fails in a noninteractive program, make that a fatal
623 error. In an interactive program (one that reads commands from the
624 user), it is better to abort the command and return to the command
625 reader loop. This allows the user to kill other processes to free up
626 virtual memory, and then try the command again.
628 @cindex command-line arguments, decoding
629 Use @code{getopt_long} to decode arguments, unless the argument syntax
630 makes this unreasonable.
632 When static storage is to be written in during program execution, use
633 explicit C code to initialize it. Reserve C initialized declarations
634 for data that will not be changed.
637 Try to avoid low-level interfaces to obscure Unix data structures (such
638 as file directories, utmp, or the layout of kernel memory), since these
639 are less likely to work compatibly. If you need to find all the files
640 in a directory, use @code{readdir} or some other high-level interface.
641 These are supported compatibly by GNU.
643 @cindex signal handling
644 The preferred signal handling facilities are the BSD variant of
645 @code{signal}, and the @sc{posix} @code{sigaction} function; the
646 alternative USG @code{signal} interface is an inferior design.
648 Nowadays, using the @sc{posix} signal functions may be the easiest way
649 to make a program portable. If you use @code{signal}, then on GNU/Linux
650 systems running GNU libc version 1, you should include
651 @file{bsd/signal.h} instead of @file{signal.h}, so as to get BSD
652 behavior. It is up to you whether to support systems where
653 @code{signal} has only the USG behavior, or give up on them.
655 @cindex impossible conditions
656 In error checks that detect ``impossible'' conditions, just abort.
657 There is usually no point in printing any message. These checks
658 indicate the existence of bugs. Whoever wants to fix the bugs will have
659 to read the source code and run a debugger. So explain the problem with
660 comments in the source. The relevant data will be in variables, which
661 are easy to examine with the debugger, so there is no point moving them
664 Do not use a count of errors as the exit status for a program.
665 @emph{That does not work}, because exit status values are limited to 8
666 bits (0 through 255). A single run of the program might have 256
667 errors; if you try to return 256 as the exit status, the parent process
668 will see 0 as the status, and it will appear that the program succeeded.
670 @cindex temporary files
671 @cindex @code{TMPDIR} environment variable
672 If you make temporary files, check the @code{TMPDIR} environment
673 variable; if that variable is defined, use the specified directory
674 instead of @file{/tmp}.
676 In addition, be aware that there is a possible security problem when
677 creating temporary files in world-writable directories. In C, you can
678 avoid this problem by creating temporary files in this manner:
681 fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0600);
685 or by using the @code{mkstemps} function from libiberty.
687 In bash, use @code{set -C} to avoid this problem.
690 @section Library Behavior
693 Try to make library functions reentrant. If they need to do dynamic
694 storage allocation, at least try to avoid any nonreentrancy aside from
695 that of @code{malloc} itself.
697 Here are certain name conventions for libraries, to avoid name
700 Choose a name prefix for the library, more than two characters long.
701 All external function and variable names should start with this
702 prefix. In addition, there should only be one of these in any given
703 library member. This usually means putting each one in a separate
706 An exception can be made when two external symbols are always used
707 together, so that no reasonable program could use one without the
708 other; then they can both go in the same file.
710 External symbols that are not documented entry points for the user
711 should have names beginning with @samp{_}. The @samp{_} should be
712 followed by the chosen name prefix for the library, to prevent
713 collisions with other libraries. These can go in the same files with
714 user entry points if you like.
716 Static functions and variables can be used as you like and need not
717 fit any naming convention.
720 @section Formatting Error Messages
721 @cindex formatting error messages
722 @cindex error messages, formatting
724 Error messages from compilers should look like this:
727 @var{source-file-name}:@var{lineno}: @var{message}
731 If you want to mention the column number, use one of these formats:
734 @var{source-file-name}:@var{lineno}:@var{column}: @var{message}
735 @var{source-file-name}:@var{lineno}.@var{column}: @var{message}
740 Line numbers should start from 1 at the beginning of the file, and
741 column numbers should start from 1 at the beginning of the line. (Both
742 of these conventions are chosen for compatibility.) Calculate column
743 numbers assuming that space and all ASCII printing characters have
744 equal width, and assuming tab stops every 8 columns.
746 The error message can also give both the starting and ending positions
747 of the erroneous text. There are several formats so that you can
748 avoid redundant information such as a duplicate line number.
749 Here are the possible formats:
752 @var{source-file-name}:@var{lineno-1}.@var{column-1}-@var{lineno-2}.@var{column-2}: @var{message}
753 @var{source-file-name}:@var{lineno-1}.@var{column-1}-@var{column-2}: @var{message}
754 @var{source-file-name}:@var{lineno-1}-@var{lineno-2}: @var{message}
758 When an error is spread over several files, you can use this format:
761 @var{file-1}:@var{lineno-1}.@var{column-1}-@var{file-2}:@var{lineno-2}.@var{column-2}: @var{message}
764 Error messages from other noninteractive programs should look like this:
767 @var{program}:@var{source-file-name}:@var{lineno}: @var{message}
771 when there is an appropriate source file, or like this:
774 @var{program}: @var{message}
778 when there is no relevant source file.
780 If you want to mention the column number, use this format:
783 @var{program}:@var{source-file-name}:@var{lineno}:@var{column}: @var{message}
786 In an interactive program (one that is reading commands from a
787 terminal), it is better not to include the program name in an error
788 message. The place to indicate which program is running is in the
789 prompt or with the screen layout. (When the same program runs with
790 input from a source other than a terminal, it is not interactive and
791 would do best to print error messages using the noninteractive style.)
793 The string @var{message} should not begin with a capital letter when
794 it follows a program name and/or file name, because that isn't the
795 beginning of a sentence. (The sentence conceptually starts at the
796 beginning of the line.) Also, it should not end with a period.
798 Error messages from interactive programs, and other messages such as
799 usage messages, should start with a capital letter. But they should not
802 @node User Interfaces
803 @section Standards for Interfaces Generally
805 @cindex program name and its behavior
806 @cindex behavior, dependent on program's name
807 Please don't make the behavior of a utility depend on the name used
808 to invoke it. It is useful sometimes to make a link to a utility
809 with a different name, and that should not change what it does.
811 Instead, use a run time option or a compilation switch or both
812 to select among the alternate behaviors.
814 @cindex output device and program's behavior
815 Likewise, please don't make the behavior of the program depend on the
816 type of output device it is used with. Device independence is an
817 important principle of the system's design; do not compromise it merely
818 to save someone from typing an option now and then. (Variation in error
819 message syntax when using a terminal is ok, because that is a side issue
820 that people do not depend on.)
822 If you think one behavior is most useful when the output is to a
823 terminal, and another is most useful when the output is a file or a
824 pipe, then it is usually best to make the default behavior the one that
825 is useful with output to a terminal, and have an option for the other
828 Compatibility requires certain programs to depend on the type of output
829 device. It would be disastrous if @code{ls} or @code{sh} did not do so
830 in the way all users expect. In some of these cases, we supplement the
831 program with a preferred alternate version that does not depend on the
832 output device type. For example, we provide a @code{dir} program much
833 like @code{ls} except that its default output format is always
837 @node Graphical Interfaces
838 @section Standards for Graphical Interfaces
839 @cindex graphical user interface
842 When you write a program that provides a graphical user interface,
843 please make it work with X Windows and the GTK+ toolkit unless the
844 functionality specifically requires some alternative (for example,
845 ``displaying jpeg images while in console mode'').
847 In addition, please provide a command-line interface to control the
848 functionality. (In many cases, the graphical user interface can be a
849 separate program which invokes the command-line program.) This is
850 so that the same jobs can be done from scripts.
854 Please also consider providing a CORBA interface (for use from GNOME), a
855 library interface (for use from C), and perhaps a keyboard-driven
856 console interface (for use by users from console mode). Once you are
857 doing the work to provide the functionality and the graphical interface,
858 these won't be much extra work.
861 @node Command-Line Interfaces
862 @section Standards for Command Line Interfaces
863 @cindex command-line interface
866 It is a good idea to follow the @sc{posix} guidelines for the
867 command-line options of a program. The easiest way to do this is to use
868 @code{getopt} to parse them. Note that the GNU version of @code{getopt}
869 will normally permit options anywhere among the arguments unless the
870 special argument @samp{--} is used. This is not what @sc{posix}
871 specifies; it is a GNU extension.
873 @cindex long-named options
874 Please define long-named options that are equivalent to the
875 single-letter Unix-style options. We hope to make GNU more user
876 friendly this way. This is easy to do with the GNU function
879 One of the advantages of long-named options is that they can be
880 consistent from program to program. For example, users should be able
881 to expect the ``verbose'' option of any GNU program which has one, to be
882 spelled precisely @samp{--verbose}. To achieve this uniformity, look at
883 the table of common long-option names when you choose the option names
884 for your program (@pxref{Option Table}).
886 It is usually a good idea for file names given as ordinary arguments to
887 be input files only; any output files would be specified using options
888 (preferably @samp{-o} or @samp{--output}). Even if you allow an output
889 file name as an ordinary argument for compatibility, try to provide an
890 option as another way to specify it. This will lead to more consistency
891 among GNU utilities, and fewer idiosyncrasies for users to remember.
893 @cindex standard command-line options
894 @cindex options, standard command-line
895 @cindex CGI programs, standard options for
896 @cindex PATH_INFO, specifying standard options as
897 All programs should support two standard options: @samp{--version}
898 and @samp{--help}. CGI programs should accept these as command-line
899 options, and also if given as the @env{PATH_INFO}; for instance,
900 visiting @url{http://example.org/p.cgi/--help} in a browser should
901 output the same information as invoking @samp{p.cgi --help} from the
905 * --version:: The standard output for --version.
906 * --help:: The standard output for --help.
910 @subsection @option{--version}
912 @cindex @samp{--version} output
914 The standard @code{--version} option should direct the program to
915 print information about its name, version, origin and legal status,
916 all on standard output, and then exit successfully. Other options and
917 arguments should be ignored once this is seen, and the program should
918 not perform its normal function.
920 @cindex canonical name of a program
921 @cindex program's canonical name
922 The first line is meant to be easy for a program to parse; the version
923 number proper starts after the last space. In addition, it contains
924 the canonical name for this program, in this format:
931 The program's name should be a constant string; @emph{don't} compute it
932 from @code{argv[0]}. The idea is to state the standard or canonical
933 name for the program, not its file name. There are other ways to find
934 out the precise file name where a command is found in @code{PATH}.
936 If the program is a subsidiary part of a larger package, mention the
937 package name in parentheses, like this:
940 emacsserver (GNU Emacs) 19.30
944 If the package has a version number which is different from this
945 program's version number, you can mention the package version number
946 just before the close-parenthesis.
948 If you @emph{need} to mention the version numbers of libraries which
949 are distributed separately from the package which contains this program,
950 you can do so by printing an additional line of version info for each
951 library you want to mention. Use the same format for these lines as for
954 Please do not mention all of the libraries that the program uses ``just
955 for completeness''---that would produce a lot of unhelpful clutter.
956 Please mention library version numbers only if you find in practice that
957 they are very important to you in debugging.
959 The following line, after the version number line or lines, should be a
960 copyright notice. If more than one copyright notice is called for, put
961 each on a separate line.
963 Next should follow a line stating the license, preferably using one of
964 abbrevations below, and a brief statement that the program is free
965 software, and that users are free to copy and change it. Also mention
966 that there is no warranty, to the extent permitted by law. See
967 recommended wording below.
969 It is ok to finish the output with a list of the major authors of the
970 program, as a way of giving credit.
972 Here's an example of output that follows these rules:
976 Copyright (C) 2007 Free Software Foundation, Inc.
977 License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
978 This is free software: you are free to change and redistribute it.
979 There is NO WARRANTY, to the extent permitted by law.
982 You should adapt this to your program, of course, filling in the proper
983 year, copyright holder, name of program, and the references to
984 distribution terms, and changing the rest of the wording as necessary.
986 This copyright notice only needs to mention the most recent year in
987 which changes were made---there's no need to list the years for previous
988 versions' changes. You don't have to mention the name of the program in
989 these notices, if that is inconvenient, since it appeared in the first
990 line. (The rules are different for copyright notices in source files;
991 @pxref{Copyright Notices,,,maintain,Information for GNU Maintainers}.)
993 Translations of the above lines must preserve the validity of the
994 copyright notices (@pxref{Internationalization}). If the translation's
995 character set supports it, the @samp{(C)} should be replaced with the
996 copyright symbol, as follows:
999 (the official copyright symbol, which is the letter C in a circle);
1005 Write the word ``Copyright'' exactly like that, in English. Do not
1006 translate it into another language. International treaties recognize
1007 the English word ``Copyright''; translations into other languages do not
1008 have legal significance.
1010 Finally, here is the table of our suggested license abbreviations.
1011 Any abbreviation can be followed by @samp{v@var{version}[+]}, meaning
1012 that particular version, or later versions with the @samp{+}, as shown
1015 In the case of exceptions for extra permissions with the GPL, we use
1016 @samp{/} for a separator; the version number can follow the license
1017 abbreviation as usual, as in the examples below.
1021 GNU General Public License, @url{http://www.gnu.org/@/licenses/@/gpl.html}.
1024 GNU Lesser General Public License, @url{http://www.gnu.org/@/licenses/@/lgpl.html}.
1027 GNU GPL with the exception for Guile; for example, GPLv3+/Guile means
1028 the GNU GPL version 3 or later, with the extra exception for Guile.
1031 GNU GPL with the exception for Ada.
1034 The Apache Software Foundation license,
1035 @url{http://www.apache.org/@/licenses}.
1038 The Artistic license used for Perl, @url{http://www.perlfoundation.org/@/legal}.
1041 The Expat license, @url{http://www.jclark.com/@/xml/@/copying.txt}.
1044 The Mozilla Public License, @url{http://www.mozilla.org/@/MPL/}.
1047 The original (4-clause) BSD license, incompatible with the GNU GPL
1048 @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#6}.
1051 The license used for PHP, @url{http://www.php.net/@/license/}.
1054 The non-license that is being in the public domain,
1055 @url{http://www.gnu.org/@/licenses/@/license-list.html#PublicDomain}.
1058 The license for Python, @url{http://www.python.org/@/2.0.1/@/license.html}.
1061 The revised (3-clause) BSD, compatible with the GNU GPL,
1062 @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#5}.
1065 The simple non-copyleft license used for most versions of the X Window
1066 system, @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#3}.
1069 The license for Zlib, @url{http://www.gzip.org/@/zlib/@/zlib_license.html}.
1073 More information about these licenses and many more are on the GNU
1074 licensing web pages,
1075 @url{http://www.gnu.org/@/licenses/@/license-list.html}.
1079 @subsection @option{--help}
1081 @cindex @samp{--help} output
1083 The standard @code{--help} option should output brief documentation
1084 for how to invoke the program, on standard output, then exit
1085 successfully. Other options and arguments should be ignored once this
1086 is seen, and the program should not perform its normal function.
1088 @cindex address for bug reports
1090 Near the end of the @samp{--help} option's output there should be a line
1091 that says where to mail bug reports. It should have this format:
1094 Report bugs to @var{mailing-address}.
1099 @section Table of Long Options
1100 @cindex long option names
1101 @cindex table of long options
1103 Here is a table of long options used by GNU programs. It is surely
1104 incomplete, but we aim to list all the options that a new program might
1105 want to be compatible with. If you use names not already in the table,
1106 please send @email{bug-standards@@gnu.org} a list of them, with their
1107 meanings, so we can update the table.
1109 @c Please leave newlines between items in this table; it's much easier
1110 @c to update when it isn't completely squashed together and unreadable.
1111 @c When there is more than one short option for a long option name, put
1112 @c a semicolon between the lists of the programs that use them, not a
1113 @c period. --friedman
1117 @samp{-N} in @code{tar}.
1120 @samp{-a} in @code{du}, @code{ls}, @code{nm}, @code{stty}, @code{uname},
1121 and @code{unexpand}.
1124 @samp{-a} in @code{diff}.
1127 @samp{-A} in @code{ls}.
1130 @samp{-a} in @code{etags}, @code{tee}, @code{time};
1131 @samp{-r} in @code{tar}.
1134 @samp{-a} in @code{cp}.
1137 @samp{-n} in @code{shar}.
1140 @samp{-l} in @code{m4}.
1143 @samp{-a} in @code{diff}.
1146 @samp{-v} in @code{gawk}.
1149 @samp{-W} in @code{make}.
1152 @samp{-o} in @code{make}.
1155 @samp{-a} in @code{recode}.
1158 @samp{-a} in @code{wdiff}.
1160 @item auto-reference
1161 @samp{-A} in @code{ptx}.
1164 @samp{-n} in @code{wdiff}.
1167 For server programs, run in the background.
1169 @item backward-search
1170 @samp{-B} in @code{ctags}.
1173 @samp{-f} in @code{shar}.
1182 @samp{-b} in @code{tac}.
1185 @samp{-b} in @code{cpio} and @code{diff}.
1188 @samp{-b} in @code{shar}.
1191 Used in @code{cpio} and @code{tar}.
1194 @samp{-b} in @code{head} and @code{tail}.
1197 @samp{-b} in @code{ptx}.
1200 Used in various programs to make output shorter.
1203 @samp{-c} in @code{head}, @code{split}, and @code{tail}.
1206 @samp{-C} in @code{etags}.
1209 @samp{-A} in @code{tar}.
1212 Used in various programs to specify the directory to use.
1215 @samp{-c} in @code{chgrp} and @code{chown}.
1218 @samp{-F} in @code{ls}.
1221 @samp{-c} in @code{recode}.
1224 @samp{-c} in @code{su};
1228 @samp{-d} in @code{tar}.
1231 Used in @code{gawk}.
1234 @samp{-Z} in @code{tar} and @code{shar}.
1237 @samp{-A} in @code{tar}.
1240 @samp{-w} in @code{tar}.
1243 Used in @code{diff}.
1246 @samp{-W copyleft} in @code{gawk}.
1249 @samp{-C} in @code{ptx}, @code{recode}, and @code{wdiff};
1250 @samp{-W copyright} in @code{gawk}.
1256 @samp{-q} in @code{who}.
1259 @samp{-l} in @code{du}.
1262 Used in @code{tar} and @code{cpio}.
1265 @samp{-c} in @code{shar}.
1268 @samp{-x} in @code{ctags}.
1271 @samp{-d} in @code{touch}.
1274 @samp{-d} in @code{make} and @code{m4};
1278 @samp{-D} in @code{m4}.
1281 @samp{-d} in Bison and @code{ctags}.
1284 @samp{-D} in @code{tar}.
1287 @samp{-L} in @code{chgrp}, @code{chown}, @code{cpio}, @code{du},
1288 @code{ls}, and @code{tar}.
1290 @item dereference-args
1291 @samp{-D} in @code{du}.
1294 Specify an I/O device (special file name).
1297 @samp{-d} in @code{recode}.
1299 @item dictionary-order
1300 @samp{-d} in @code{look}.
1303 @samp{-d} in @code{tar}.
1306 @samp{-n} in @code{csplit}.
1309 Specify the directory to use, in various programs. In @code{ls}, it
1310 means to show directories themselves rather than their contents. In
1311 @code{rm} and @code{ln}, it means to not treat links to directories
1315 @samp{-x} in @code{strip}.
1317 @item discard-locals
1318 @samp{-X} in @code{strip}.
1321 @samp{-n} in @code{make}.
1324 @samp{-e} in @code{diff}.
1326 @item elide-empty-files
1327 @samp{-z} in @code{csplit}.
1330 @samp{-x} in @code{wdiff}.
1333 @samp{-z} in @code{wdiff}.
1335 @item entire-new-file
1336 @samp{-N} in @code{diff}.
1338 @item environment-overrides
1339 @samp{-e} in @code{make}.
1342 @samp{-e} in @code{xargs}.
1348 Used in @code{makeinfo}.
1351 @samp{-o} in @code{m4}.
1354 @samp{-b} in @code{ls}.
1357 @samp{-X} in @code{tar}.
1363 @samp{-x} in @code{xargs}.
1366 @samp{-e} in @code{unshar}.
1369 @samp{-t} in @code{diff}.
1372 @samp{-e} in @code{sed}.
1375 @samp{-g} in @code{nm}.
1378 @samp{-i} in @code{cpio};
1379 @samp{-x} in @code{tar}.
1382 @samp{-f} in @code{finger}.
1385 @samp{-f} in @code{su}.
1387 @item fatal-warnings
1388 @samp{-E} in @code{m4}.
1391 @samp{-f} in @code{gawk}, @code{info}, @code{make}, @code{mt},
1392 @code{sed}, and @code{tar}.
1394 @item field-separator
1395 @samp{-F} in @code{gawk}.
1401 @samp{-F} in @code{ls}.
1404 @samp{-T} in @code{tar}.
1407 Used in @code{makeinfo}.
1409 @item flag-truncation
1410 @samp{-F} in @code{ptx}.
1412 @item fixed-output-files
1416 @samp{-f} in @code{tail}.
1418 @item footnote-style
1419 Used in @code{makeinfo}.
1422 @samp{-f} in @code{cp}, @code{ln}, @code{mv}, and @code{rm}.
1425 @samp{-F} in @code{shar}.
1428 For server programs, run in the foreground;
1429 in other words, don't do anything special to run the server
1433 Used in @code{ls}, @code{time}, and @code{ptx}.
1436 @samp{-F} in @code{m4}.
1442 @samp{-g} in @code{ptx}.
1445 @samp{-x} in @code{tar}.
1448 @samp{-i} in @code{ul}.
1451 @samp{-g} in @code{recode}.
1454 @samp{-g} in @code{install}.
1457 @samp{-z} in @code{tar} and @code{shar}.
1460 @samp{-H} in @code{m4}.
1463 @samp{-h} in @code{objdump} and @code{recode}
1466 @samp{-H} in @code{who}.
1469 Used to ask for brief usage information.
1471 @item here-delimiter
1472 @samp{-d} in @code{shar}.
1474 @item hide-control-chars
1475 @samp{-q} in @code{ls}.
1478 In @code{makeinfo}, output HTML.
1481 @samp{-u} in @code{who}.
1484 @samp{-D} in @code{diff}.
1487 @samp{-I} in @code{ls};
1488 @samp{-x} in @code{recode}.
1490 @item ignore-all-space
1491 @samp{-w} in @code{diff}.
1493 @item ignore-backups
1494 @samp{-B} in @code{ls}.
1496 @item ignore-blank-lines
1497 @samp{-B} in @code{diff}.
1500 @samp{-f} in @code{look} and @code{ptx};
1501 @samp{-i} in @code{diff} and @code{wdiff}.
1504 @samp{-i} in @code{make}.
1507 @samp{-i} in @code{ptx}.
1509 @item ignore-indentation
1510 @samp{-I} in @code{etags}.
1512 @item ignore-init-file
1515 @item ignore-interrupts
1516 @samp{-i} in @code{tee}.
1518 @item ignore-matching-lines
1519 @samp{-I} in @code{diff}.
1521 @item ignore-space-change
1522 @samp{-b} in @code{diff}.
1525 @samp{-i} in @code{tar}.
1528 @samp{-i} in @code{etags};
1529 @samp{-I} in @code{m4}.
1532 @samp{-I} in @code{make}.
1535 @samp{-G} in @code{tar}.
1538 @samp{-i}, @samp{-l}, and @samp{-m} in Finger.
1541 In some programs, specify the name of the file to read as the user's
1545 @samp{-i} in @code{expand}.
1548 @samp{-T} in @code{diff}.
1551 @samp{-i} in @code{ls}.
1554 @samp{-i} in @code{cp}, @code{ln}, @code{mv}, @code{rm};
1555 @samp{-e} in @code{m4};
1556 @samp{-p} in @code{xargs};
1557 @samp{-w} in @code{tar}.
1560 @samp{-p} in @code{shar}.
1566 @samp{-j} in @code{make}.
1569 @samp{-n} in @code{make}.
1572 @samp{-k} in @code{make}.
1575 @samp{-k} in @code{csplit}.
1578 @samp{-k} in @code{du} and @code{ls}.
1581 @samp{-l} in @code{etags}.
1584 @samp{-l} in @code{wdiff}.
1586 @item level-for-gzip
1587 @samp{-g} in @code{shar}.
1590 @samp{-C} in @code{split}.
1593 Used in @code{split}, @code{head}, and @code{tail}.
1596 @samp{-l} in @code{cpio}.
1600 Used in @code{gawk}.
1603 @samp{-t} in @code{cpio};
1604 @samp{-l} in @code{recode}.
1607 @samp{-t} in @code{tar}.
1610 @samp{-N} in @code{ls}.
1613 @samp{-l} in @code{make}.
1619 Used in @code{uname}.
1622 @samp{-M} in @code{ptx}.
1625 @samp{-m} in @code{hello} and @code{uname}.
1627 @item make-directories
1628 @samp{-d} in @code{cpio}.
1631 @samp{-f} in @code{make}.
1637 @samp{-n} in @code{xargs}.
1640 @samp{-n} in @code{xargs}.
1643 @samp{-l} in @code{xargs}.
1646 @samp{-l} in @code{make}.
1649 @samp{-P} in @code{xargs}.
1652 @samp{-T} in @code{who}.
1655 @samp{-T} in @code{who}.
1658 @samp{-d} in @code{diff}.
1660 @item mixed-uuencode
1661 @samp{-M} in @code{shar}.
1664 @samp{-m} in @code{install}, @code{mkdir}, and @code{mkfifo}.
1666 @item modification-time
1667 @samp{-m} in @code{tar}.
1670 @samp{-M} in @code{tar}.
1676 @samp{-L} in @code{m4}.
1679 @samp{-a} in @code{shar}.
1682 @samp{-W} in @code{make}.
1684 @item no-builtin-rules
1685 @samp{-r} in @code{make}.
1687 @item no-character-count
1688 @samp{-w} in @code{shar}.
1690 @item no-check-existing
1691 @samp{-x} in @code{shar}.
1694 @samp{-3} in @code{wdiff}.
1697 @samp{-c} in @code{touch}.
1700 @samp{-D} in @code{etags}.
1703 @samp{-1} in @code{wdiff}.
1705 @item no-dereference
1706 @samp{-d} in @code{cp}.
1709 @samp{-2} in @code{wdiff}.
1712 @samp{-S} in @code{make}.
1718 @samp{-P} in @code{shar}.
1721 @samp{-e} in @code{gprof}.
1724 @samp{-R} in @code{etags}.
1727 @samp{-p} in @code{nm}.
1730 Don't print a startup splash screen.
1733 Used in @code{makeinfo}.
1736 @samp{-a} in @code{gprof}.
1739 @samp{-E} in @code{gprof}.
1742 @samp{-m} in @code{shar}.
1745 Used in @code{makeinfo}.
1748 Used in @code{emacsclient}.
1751 Used in various programs to inhibit warnings.
1754 @samp{-n} in @code{info}.
1757 @samp{-n} in @code{uname}.
1760 @samp{-f} in @code{cpio}.
1763 @samp{-n} in @code{objdump}.
1766 @samp{-0} in @code{xargs}.
1769 @samp{-n} in @code{cat}.
1771 @item number-nonblank
1772 @samp{-b} in @code{cat}.
1775 @samp{-n} in @code{nm}.
1777 @item numeric-uid-gid
1778 @samp{-n} in @code{cpio} and @code{ls}.
1784 @samp{-o} in @code{tar}.
1787 @samp{-o} in @code{make}.
1789 @item one-file-system
1790 @samp{-l} in @code{tar}, @code{cp}, and @code{du}.
1793 @samp{-o} in @code{ptx}.
1796 @samp{-f} in @code{gprof}.
1799 @samp{-F} in @code{gprof}.
1802 @samp{-o} in @code{getopt}, @code{fdlist}, @code{fdmount},
1803 @code{fdmountd}, and @code{fdumount}.
1806 In various programs, specify the output file name.
1809 @samp{-o} in @code{shar}.
1812 @samp{-o} in @code{rm}.
1815 @samp{-c} in @code{unshar}.
1818 @samp{-o} in @code{install}.
1821 @samp{-l} in @code{diff}.
1823 @item paragraph-indent
1824 Used in @code{makeinfo}.
1827 @samp{-p} in @code{mkdir} and @code{rmdir}.
1830 @samp{-p} in @code{ul}.
1833 @samp{-p} in @code{cpio}.
1836 @samp{-P} in @code{finger}.
1839 @samp{-c} in @code{cpio} and @code{tar}.
1842 Used in @code{gawk}.
1844 @item prefix-builtins
1845 @samp{-P} in @code{m4}.
1848 @samp{-f} in @code{csplit}.
1851 Used in @code{tar} and @code{cp}.
1853 @item preserve-environment
1854 @samp{-p} in @code{su}.
1856 @item preserve-modification-time
1857 @samp{-m} in @code{cpio}.
1859 @item preserve-order
1860 @samp{-s} in @code{tar}.
1862 @item preserve-permissions
1863 @samp{-p} in @code{tar}.
1866 @samp{-l} in @code{diff}.
1869 @samp{-L} in @code{cmp}.
1871 @item print-data-base
1872 @samp{-p} in @code{make}.
1874 @item print-directory
1875 @samp{-w} in @code{make}.
1877 @item print-file-name
1878 @samp{-o} in @code{nm}.
1881 @samp{-s} in @code{nm}.
1884 @samp{-p} in @code{wdiff}.
1887 @samp{-p} in @code{ed}.
1890 Specify an HTTP proxy.
1893 @samp{-X} in @code{shar}.
1896 @samp{-q} in @code{make}.
1899 Used in many programs to inhibit the usual output. Every
1900 program accepting @samp{--quiet} should accept @samp{--silent} as a
1904 @samp{-Q} in @code{shar}
1907 @samp{-Q} in @code{ls}.
1910 @samp{-n} in @code{diff}.
1913 Used in @code{gawk}.
1915 @item read-full-blocks
1916 @samp{-B} in @code{tar}.
1922 @samp{-n} in @code{make}.
1925 @samp{-R} in @code{tar}.
1928 Used in @code{chgrp}, @code{chown}, @code{cp}, @code{ls}, @code{diff},
1932 @samp{-r} in @code{touch}.
1935 @samp{-r} in @code{ptx}.
1938 @samp{-r} in @code{tac} and @code{etags}.
1941 @samp{-r} in @code{uname}.
1944 @samp{-R} in @code{m4}.
1947 @samp{-r} in @code{objdump}.
1950 @samp{-r} in @code{cpio}.
1953 @samp{-i} in @code{xargs}.
1955 @item report-identical-files
1956 @samp{-s} in @code{diff}.
1958 @item reset-access-time
1959 @samp{-a} in @code{cpio}.
1962 @samp{-r} in @code{ls} and @code{nm}.
1965 @samp{-f} in @code{diff}.
1967 @item right-side-defs
1968 @samp{-R} in @code{ptx}.
1971 @samp{-s} in @code{tar}.
1973 @item same-permissions
1974 @samp{-p} in @code{tar}.
1977 @samp{-g} in @code{stty}.
1982 @item sentence-regexp
1983 @samp{-S} in @code{ptx}.
1986 @samp{-S} in @code{du}.
1989 @samp{-s} in @code{tac}.
1992 Used by @code{recode} to chose files or pipes for sequencing passes.
1995 @samp{-s} in @code{su}.
1998 @samp{-A} in @code{cat}.
2000 @item show-c-function
2001 @samp{-p} in @code{diff}.
2004 @samp{-E} in @code{cat}.
2006 @item show-function-line
2007 @samp{-F} in @code{diff}.
2010 @samp{-T} in @code{cat}.
2013 Used in many programs to inhibit the usual output.
2014 Every program accepting
2015 @samp{--silent} should accept @samp{--quiet} as a synonym.
2018 @samp{-s} in @code{ls}.
2021 Specify a file descriptor for a network server to use for its socket,
2022 instead of opening and binding a new socket. This provides a way to
2023 run, in a non-privileged process, a server that normally needs a
2024 reserved port number.
2030 @samp{-W source} in @code{gawk}.
2033 @samp{-S} in @code{tar}.
2035 @item speed-large-files
2036 @samp{-H} in @code{diff}.
2039 @samp{-E} in @code{unshar}.
2041 @item split-size-limit
2042 @samp{-L} in @code{shar}.
2045 @samp{-s} in @code{cat}.
2048 @samp{-w} in @code{wdiff}.
2051 @samp{-y} in @code{wdiff}.
2054 Used in @code{tar} and @code{diff} to specify which file within
2055 a directory to start processing with.
2058 @samp{-s} in @code{wdiff}.
2060 @item stdin-file-list
2061 @samp{-S} in @code{shar}.
2064 @samp{-S} in @code{make}.
2067 @samp{-s} in @code{recode}.
2070 @samp{-s} in @code{install}.
2073 @samp{-s} in @code{strip}.
2076 @samp{-S} in @code{strip}.
2079 @samp{-s} in @code{shar}.
2082 @samp{-S} in @code{cp}, @code{ln}, @code{mv}.
2085 @samp{-b} in @code{csplit}.
2088 @samp{-s} in @code{gprof}.
2091 @samp{-s} in @code{du}.
2094 @samp{-s} in @code{ln}.
2097 Used in GDB and @code{objdump}.
2100 @samp{-s} in @code{m4}.
2103 @samp{-s} in @code{uname}.
2106 @samp{-t} in @code{expand} and @code{unexpand}.
2109 @samp{-T} in @code{ls}.
2112 @samp{-T} in @code{tput} and @code{ul}.
2113 @samp{-t} in @code{wdiff}.
2116 @samp{-a} in @code{diff}.
2119 @samp{-T} in @code{shar}.
2122 Used in @code{ls} and @code{touch}.
2125 Specify how long to wait before giving up on some operation.
2128 @samp{-O} in @code{tar}.
2131 @samp{-c} in @code{du}.
2134 @samp{-t} in @code{make}, @code{ranlib}, and @code{recode}.
2137 @samp{-t} in @code{m4}.
2140 @samp{-t} in @code{hello};
2141 @samp{-W traditional} in @code{gawk};
2142 @samp{-G} in @code{ed}, @code{m4}, and @code{ptx}.
2148 @samp{-t} in @code{ctags}.
2150 @item typedefs-and-c++
2151 @samp{-T} in @code{ctags}.
2154 @samp{-t} in @code{ptx}.
2157 @samp{-z} in @code{tar}.
2160 @samp{-u} in @code{cpio}.
2163 @samp{-U} in @code{m4}.
2165 @item undefined-only
2166 @samp{-u} in @code{nm}.
2169 @samp{-u} in @code{cp}, @code{ctags}, @code{mv}, @code{tar}.
2172 Used in @code{gawk}; same as @samp{--help}.
2175 @samp{-B} in @code{shar}.
2177 @item vanilla-operation
2178 @samp{-V} in @code{shar}.
2181 Print more information about progress. Many programs support this.
2184 @samp{-W} in @code{tar}.
2187 Print the version number.
2189 @item version-control
2190 @samp{-V} in @code{cp}, @code{ln}, @code{mv}.
2193 @samp{-v} in @code{ctags}.
2196 @samp{-V} in @code{tar}.
2199 @samp{-W} in @code{make}.
2201 @item whole-size-limit
2202 @samp{-l} in @code{shar}.
2205 @samp{-w} in @code{ls} and @code{ptx}.
2208 @samp{-W} in @code{ptx}.
2211 @samp{-T} in @code{who}.
2214 @samp{-z} in @code{gprof}.
2217 @node OID Allocations
2218 @section OID Allocations
2219 @cindex OID allocations for GNU
2224 The OID (object identifier) 1.3.6.1.4.1.11591 has been assigned to the
2225 GNU Project (thanks to Werner Koch). These are used for SNMP, LDAP,
2226 X.509 certificates, and so on. The web site
2227 @url{http://www.alvestrand.no/objectid} has a (voluntary) listing of
2228 many OID assignments.
2230 If you need a new slot for your GNU package, write
2231 @email{maintainers@@gnu.org}. Here is a list of arcs currently
2235 @include gnu-oids.texi
2240 @section Memory Usage
2241 @cindex memory usage
2243 If a program typically uses just a few meg of memory, don't bother making any
2244 effort to reduce memory usage. For example, if it is impractical for
2245 other reasons to operate on files more than a few meg long, it is
2246 reasonable to read entire input files into memory to operate on them.
2248 However, for programs such as @code{cat} or @code{tail}, that can
2249 usefully operate on very large files, it is important to avoid using a
2250 technique that would artificially limit the size of files it can handle.
2251 If a program works by lines and could be applied to arbitrary
2252 user-supplied input files, it should keep only a line in memory, because
2253 this is not very hard and users will want to be able to operate on input
2254 files that are bigger than will fit in memory all at once.
2256 If your program creates complicated data structures, just make them in
2257 memory and give a fatal error if @code{malloc} returns zero.
2263 Programs should be prepared to operate when @file{/usr} and @file{/etc}
2264 are read-only file systems. Thus, if the program manages log files,
2265 lock files, backup files, score files, or any other files which are
2266 modified for internal purposes, these files should not be stored in
2267 @file{/usr} or @file{/etc}.
2269 There are two exceptions. @file{/etc} is used to store system
2270 configuration information; it is reasonable for a program to modify
2271 files in @file{/etc} when its job is to update the system configuration.
2272 Also, if the user explicitly asks to modify one file in a directory, it
2273 is reasonable for the program to store other files in the same
2277 @chapter Making The Best Use of C
2279 This chapter provides advice on how best to use the C language
2280 when writing GNU software.
2283 * Formatting:: Formatting your source code.
2284 * Comments:: Commenting your work.
2285 * Syntactic Conventions:: Clean use of C constructs.
2286 * Names:: Naming variables, functions, and files.
2287 * System Portability:: Portability among different operating systems.
2288 * CPU Portability:: Supporting the range of CPU types.
2289 * System Functions:: Portability and ``standard'' library functions.
2290 * Internationalization:: Techniques for internationalization.
2291 * Character Set:: Use ASCII by default.
2292 * Quote Characters:: Use `...' in the C locale.
2293 * Mmap:: How you can safely use @code{mmap}.
2297 @section Formatting Your Source Code
2298 @cindex formatting source code
2301 @cindex braces, in C source
2302 It is important to put the open-brace that starts the body of a C
2303 function in column one, so that they will start a defun. Several
2304 tools look for open-braces in column one to find the beginnings of C
2305 functions. These tools will not work on code not formatted that way.
2307 Avoid putting open-brace, open-parenthesis or open-bracket in column
2308 one when they are inside a function, so that they won't start a defun.
2309 The open-brace that starts a @code{struct} body can go in column one
2310 if you find it useful to treat that definition as a defun.
2312 It is also important for function definitions to start the name of the
2313 function in column one. This helps people to search for function
2314 definitions, and may also help certain tools recognize them. Thus,
2315 using Standard C syntax, the format is this:
2319 concat (char *s1, char *s2)
2326 or, if you want to use traditional C syntax, format the definition like
2331 concat (s1, s2) /* Name starts in column one here */
2333 @{ /* Open brace in column one here */
2338 In Standard C, if the arguments don't fit nicely on one line,
2343 lots_of_args (int an_integer, long a_long, short a_short,
2344 double a_double, float a_float)
2348 The rest of this section gives our recommendations for other aspects of
2349 C formatting style, which is also the default style of the @code{indent}
2350 program in version 1.2 and newer. It corresponds to the options
2353 -nbad -bap -nbc -bbo -bl -bli2 -bls -ncdb -nce -cp1 -cs -di2
2354 -ndj -nfc1 -nfca -hnl -i2 -ip5 -lp -pcs -psl -nsc -nsob
2357 We don't think of these recommendations as requirements, because it
2358 causes no problems for users if two different programs have different
2361 But whatever style you use, please use it consistently, since a mixture
2362 of styles within one program tends to look ugly. If you are
2363 contributing changes to an existing program, please follow the style of
2366 For the body of the function, our recommended style looks like this:
2378 return ++x + bar ();
2382 @cindex spaces before open-paren
2383 We find it easier to read a program when it has spaces before the
2384 open-parentheses and after the commas. Especially after the commas.
2386 When you split an expression into multiple lines, split it
2387 before an operator, not after one. Here is the right way:
2389 @cindex expressions, splitting
2391 if (foo_this_is_long && bar > win (x, y, z)
2392 && remaining_condition)
2395 Try to avoid having two operators of different precedence at the same
2396 level of indentation. For example, don't write this:
2399 mode = (inmode[j] == VOIDmode
2400 || GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])
2401 ? outmode[j] : inmode[j]);
2404 Instead, use extra parentheses so that the indentation shows the nesting:
2407 mode = ((inmode[j] == VOIDmode
2408 || (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])))
2409 ? outmode[j] : inmode[j]);
2412 Insert extra parentheses so that Emacs will indent the code properly.
2413 For example, the following indentation looks nice if you do it by hand,
2416 v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
2417 + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000;
2421 but Emacs would alter it. Adding a set of parentheses produces
2422 something that looks equally nice, and which Emacs will preserve:
2425 v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
2426 + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000);
2429 Format do-while statements like this:
2441 Please use formfeed characters (control-L) to divide the program into
2442 pages at logical places (but not within a function). It does not matter
2443 just how long the pages are, since they do not have to fit on a printed
2444 page. The formfeeds should appear alone on lines by themselves.
2447 @section Commenting Your Work
2450 Every program should start with a comment saying briefly what it is for.
2451 Example: @samp{fmt - filter for simple filling of text}. This comment
2452 should be at the top of the source file containing the @samp{main}
2453 function of the program.
2455 Also, please write a brief comment at the start of each source file,
2456 with the file name and a line or two about the overall purpose of the
2459 Please write the comments in a GNU program in English, because English
2460 is the one language that nearly all programmers in all countries can
2461 read. If you do not write English well, please write comments in
2462 English as well as you can, then ask other people to help rewrite them.
2463 If you can't write comments in English, please find someone to work with
2464 you and translate your comments into English.
2466 Please put a comment on each function saying what the function does,
2467 what sorts of arguments it gets, and what the possible values of
2468 arguments mean and are used for. It is not necessary to duplicate in
2469 words the meaning of the C argument declarations, if a C type is being
2470 used in its customary fashion. If there is anything nonstandard about
2471 its use (such as an argument of type @code{char *} which is really the
2472 address of the second character of a string, not the first), or any
2473 possible values that would not work the way one would expect (such as,
2474 that strings containing newlines are not guaranteed to work), be sure
2477 Also explain the significance of the return value, if there is one.
2479 Please put two spaces after the end of a sentence in your comments, so
2480 that the Emacs sentence commands will work. Also, please write
2481 complete sentences and capitalize the first word. If a lower-case
2482 identifier comes at the beginning of a sentence, don't capitalize it!
2483 Changing the spelling makes it a different identifier. If you don't
2484 like starting a sentence with a lower case letter, write the sentence
2485 differently (e.g., ``The identifier lower-case is @dots{}'').
2487 The comment on a function is much clearer if you use the argument
2488 names to speak about the argument values. The variable name itself
2489 should be lower case, but write it in upper case when you are speaking
2490 about the value rather than the variable itself. Thus, ``the inode
2491 number NODE_NUM'' rather than ``an inode''.
2493 There is usually no purpose in restating the name of the function in
2494 the comment before it, because the reader can see that for himself.
2495 There might be an exception when the comment is so long that the function
2496 itself would be off the bottom of the screen.
2498 There should be a comment on each static variable as well, like this:
2501 /* Nonzero means truncate lines in the display;
2502 zero means continue them. */
2506 @cindex conditionals, comments for
2507 @cindex @code{#endif}, commenting
2508 Every @samp{#endif} should have a comment, except in the case of short
2509 conditionals (just a few lines) that are not nested. The comment should
2510 state the condition of the conditional that is ending, @emph{including
2511 its sense}. @samp{#else} should have a comment describing the condition
2512 @emph{and sense} of the code that follows. For example:
2520 #endif /* not foo */
2530 but, by contrast, write the comments this way for a @samp{#ifndef}:
2543 #endif /* not foo */
2547 @node Syntactic Conventions
2548 @section Clean Use of C Constructs
2549 @cindex syntactic conventions
2551 @cindex implicit @code{int}
2552 @cindex function argument, declaring
2553 Please explicitly declare the types of all objects. For example, you
2554 should explicitly declare all arguments to functions, and you should
2555 declare functions to return @code{int} rather than omitting the
2558 @cindex compiler warnings
2559 @cindex @samp{-Wall} compiler option
2560 Some programmers like to use the GCC @samp{-Wall} option, and change the
2561 code whenever it issues a warning. If you want to do this, then do.
2562 Other programmers prefer not to use @samp{-Wall}, because it gives
2563 warnings for valid and legitimate code which they do not want to change.
2564 If you want to do this, then do. The compiler should be your servant,
2567 Declarations of external functions and functions to appear later in the
2568 source file should all go in one place near the beginning of the file
2569 (somewhere before the first function definition in the file), or else
2570 should go in a header file. Don't put @code{extern} declarations inside
2573 @cindex temporary variables
2574 It used to be common practice to use the same local variables (with
2575 names like @code{tem}) over and over for different values within one
2576 function. Instead of doing this, it is better to declare a separate local
2577 variable for each distinct purpose, and give it a name which is
2578 meaningful. This not only makes programs easier to understand, it also
2579 facilitates optimization by good compilers. You can also move the
2580 declaration of each local variable into the smallest scope that includes
2581 all its uses. This makes the program even cleaner.
2583 Don't use local variables or parameters that shadow global identifiers.
2585 @cindex multiple variables in a line
2586 Don't declare multiple variables in one declaration that spans lines.
2587 Start a new declaration on each line, instead. For example, instead
2613 (If they are global variables, each should have a comment preceding it
2616 When you have an @code{if}-@code{else} statement nested in another
2617 @code{if} statement, always put braces around the @code{if}-@code{else}.
2618 Thus, never write like this:
2641 If you have an @code{if} statement nested inside of an @code{else}
2642 statement, either write @code{else if} on one line, like this,
2652 with its @code{then}-part indented like the preceding @code{then}-part,
2653 or write the nested @code{if} within braces like this:
2665 Don't declare both a structure tag and variables or typedefs in the
2666 same declaration. Instead, declare the structure tag separately
2667 and then use it to declare the variables or typedefs.
2669 Try to avoid assignments inside @code{if}-conditions (assignments
2670 inside @code{while}-conditions are ok). For example, don't write
2674 if ((foo = (char *) malloc (sizeof *foo)) == 0)
2675 fatal ("virtual memory exhausted");
2679 instead, write this:
2682 foo = (char *) malloc (sizeof *foo);
2684 fatal ("virtual memory exhausted");
2688 Don't make the program ugly to placate @code{lint}. Please don't insert any
2689 casts to @code{void}. Zero without a cast is perfectly fine as a null
2690 pointer constant, except when calling a varargs function.
2693 @section Naming Variables, Functions, and Files
2695 @cindex names of variables, functions, and files
2696 The names of global variables and functions in a program serve as
2697 comments of a sort. So don't choose terse names---instead, look for
2698 names that give useful information about the meaning of the variable or
2699 function. In a GNU program, names should be English, like other
2702 Local variable names can be shorter, because they are used only within
2703 one context, where (presumably) comments explain their purpose.
2705 Try to limit your use of abbreviations in symbol names. It is ok to
2706 make a few abbreviations, explain what they mean, and then use them
2707 frequently, but don't use lots of obscure abbreviations.
2709 Please use underscores to separate words in a name, so that the Emacs
2710 word commands can be useful within them. Stick to lower case; reserve
2711 upper case for macros and @code{enum} constants, and for name-prefixes
2712 that follow a uniform convention.
2714 For example, you should use names like @code{ignore_space_change_flag};
2715 don't use names like @code{iCantReadThis}.
2717 Variables that indicate whether command-line options have been
2718 specified should be named after the meaning of the option, not after
2719 the option-letter. A comment should state both the exact meaning of
2720 the option and its letter. For example,
2724 /* Ignore changes in horizontal whitespace (-b). */
2725 int ignore_space_change_flag;
2729 When you want to define names with constant integer values, use
2730 @code{enum} rather than @samp{#define}. GDB knows about enumeration
2733 @cindex file-name limitations
2735 You might want to make sure that none of the file names would conflict
2736 if the files were loaded onto an MS-DOS file system which shortens the
2737 names. You can use the program @code{doschk} to test for this.
2739 Some GNU programs were designed to limit themselves to file names of 14
2740 characters or less, to avoid file name conflicts if they are read into
2741 older System V systems. Please preserve this feature in the existing
2742 GNU programs that have it, but there is no need to do this in new GNU
2743 programs. @code{doschk} also reports file names longer than 14
2746 @node System Portability
2747 @section Portability between System Types
2748 @cindex portability, between system types
2750 In the Unix world, ``portability'' refers to porting to different Unix
2751 versions. For a GNU program, this kind of portability is desirable, but
2754 The primary purpose of GNU software is to run on top of the GNU kernel,
2755 compiled with the GNU C compiler, on various types of @sc{cpu}. So the
2756 kinds of portability that are absolutely necessary are quite limited.
2757 But it is important to support Linux-based GNU systems, since they
2758 are the form of GNU that is popular.
2760 Beyond that, it is good to support the other free operating systems
2761 (*BSD), and it is nice to support other Unix-like systems if you want
2762 to. Supporting a variety of Unix-like systems is desirable, although
2763 not paramount. It is usually not too hard, so you may as well do it.
2764 But you don't have to consider it an obligation, if it does turn out to
2768 The easiest way to achieve portability to most Unix-like systems is to
2769 use Autoconf. It's unlikely that your program needs to know more
2770 information about the host platform than Autoconf can provide, simply
2771 because most of the programs that need such knowledge have already been
2774 Avoid using the format of semi-internal data bases (e.g., directories)
2775 when there is a higher-level alternative (@code{readdir}).
2777 @cindex non-@sc{posix} systems, and portability
2778 As for systems that are not like Unix, such as MSDOS, Windows, VMS, MVS,
2779 and older Macintosh systems, supporting them is often a lot of work.
2780 When that is the case, it is better to spend your time adding features
2781 that will be useful on GNU and GNU/Linux, rather than on supporting
2782 other incompatible systems.
2784 If you do support Windows, please do not abbreviate it as ``win''. In
2785 hacker terminology, calling something a ``win'' is a form of praise.
2786 You're free to praise Microsoft Windows on your own if you want, but
2787 please don't do this in GNU packages. Instead of abbreviating
2788 ``Windows'' to ``win'', you can write it in full or abbreviate it to
2789 ``woe'' or ``w''. In GNU Emacs, for instance, we use @samp{w32} in
2790 file names of Windows-specific files, but the macro for Windows
2791 conditionals is called @code{WINDOWSNT}.
2793 It is a good idea to define the ``feature test macro''
2794 @code{_GNU_SOURCE} when compiling your C files. When you compile on GNU
2795 or GNU/Linux, this will enable the declarations of GNU library extension
2796 functions, and that will usually give you a compiler error message if
2797 you define the same function names in some other way in your program.
2798 (You don't have to actually @emph{use} these functions, if you prefer
2799 to make the program more portable to other systems.)
2801 But whether or not you use these GNU extensions, you should avoid
2802 using their names for any other meanings. Doing so would make it hard
2803 to move your code into other GNU programs.
2805 @node CPU Portability
2806 @section Portability between @sc{cpu}s
2808 @cindex data types, and portability
2809 @cindex portability, and data types
2810 Even GNU systems will differ because of differences among @sc{cpu}
2811 types---for example, difference in byte ordering and alignment
2812 requirements. It is absolutely essential to handle these differences.
2813 However, don't make any effort to cater to the possibility that an
2814 @code{int} will be less than 32 bits. We don't support 16-bit machines
2817 Similarly, don't make any effort to cater to the possibility that
2818 @code{long} will be smaller than predefined types like @code{size_t}.
2819 For example, the following code is ok:
2822 printf ("size = %lu\n", (unsigned long) sizeof array);
2823 printf ("diff = %ld\n", (long) (pointer2 - pointer1));
2826 1989 Standard C requires this to work, and we know of only one
2827 counterexample: 64-bit programs on Microsoft Windows. We will
2828 leave it to those who want to port GNU programs to that environment
2829 to figure out how to do it.
2831 Predefined file-size types like @code{off_t} are an exception: they are
2832 longer than @code{long} on many platforms, so code like the above won't
2833 work with them. One way to print an @code{off_t} value portably is to
2834 print its digits yourself, one by one.
2836 Don't assume that the address of an @code{int} object is also the
2837 address of its least-significant byte. This is false on big-endian
2838 machines. Thus, don't make the following mistake:
2843 while ((c = getchar ()) != EOF)
2844 write (file_descriptor, &c, 1);
2847 @noindent Instead, use @code{unsigned char} as follows. (The @code{unsigned}
2848 is for portability to unusual systems where @code{char} is signed and
2849 where there is integer overflow checking.)
2853 while ((c = getchar ()) != EOF)
2855 unsigned char u = c;
2856 write (file_descriptor, &u, 1);
2860 It used to be ok to not worry about the difference between pointers
2861 and integers when passing arguments to functions. However, on most
2862 modern 64-bit machines pointers are wider than @code{int}.
2863 Conversely, integer types like @code{long long int} and @code{off_t}
2864 are wider than pointers on most modern 32-bit machines. Hence it's
2865 often better nowadays to use prototypes to define functions whose
2866 argument types are not trivial.
2868 In particular, if functions accept varying argument counts or types
2869 they should be declared using prototypes containing @samp{...} and
2870 defined using @file{stdarg.h}. For an example of this, please see the
2871 @uref{http://www.gnu.org/software/gnulib/, Gnulib} error module, which
2872 declares and defines the following function:
2875 /* Print a message with `fprintf (stderr, FORMAT, ...)';
2876 if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM).
2877 If STATUS is nonzero, terminate the program with `exit (STATUS)'. */
2879 void error (int status, int errnum, const char *format, ...);
2882 A simple way to use the Gnulib error module is to obtain the two
2883 source files @file{error.c} and @file{error.h} from the Gnulib library
2884 source code repository at
2885 @uref{http://git.savannah.gnu.org/@/gitweb/@/?p=gnulib.git}.
2886 Here's a sample use:
2893 char *program_name = "myprogram";
2896 xfopen (char const *name)
2898 FILE *fp = fopen (name, "r");
2900 error (1, errno, "cannot read %s", name);
2905 @cindex casting pointers to integers
2906 Avoid casting pointers to integers if you can. Such casts greatly
2907 reduce portability, and in most programs they are easy to avoid. In the
2908 cases where casting pointers to integers is essential---such as, a Lisp
2909 interpreter which stores type information as well as an address in one
2910 word---you'll have to make explicit provisions to handle different word
2911 sizes. You will also need to make provision for systems in which the
2912 normal range of addresses you can get from @code{malloc} starts far away
2915 @node System Functions
2916 @section Calling System Functions
2917 @cindex library functions, and portability
2918 @cindex portability, and library functions
2920 C implementations differ substantially. Standard C reduces but does
2921 not eliminate the incompatibilities; meanwhile, many GNU packages still
2922 support pre-standard compilers because this is not hard to do. This
2923 chapter gives recommendations for how to use the more-or-less standard C
2924 library functions to avoid unnecessary loss of portability.
2928 Don't use the return value of @code{sprintf}. It returns the number of
2929 characters written on some systems, but not on all systems.
2932 Be aware that @code{vfprintf} is not always available.
2935 @code{main} should be declared to return type @code{int}. It should
2936 terminate either by calling @code{exit} or by returning the integer
2937 status code; make sure it cannot ever return an undefined value.
2939 @cindex declaration for system functions
2941 Don't declare system functions explicitly.
2943 Almost any declaration for a system function is wrong on some system.
2944 To minimize conflicts, leave it to the system header files to declare
2945 system functions. If the headers don't declare a function, let it
2948 While it may seem unclean to use a function without declaring it, in
2949 practice this works fine for most system library functions on the
2950 systems where this really happens; thus, the disadvantage is only
2951 theoretical. By contrast, actual declarations have frequently caused
2955 If you must declare a system function, don't specify the argument types.
2956 Use an old-style declaration, not a Standard C prototype. The more you
2957 specify about the function, the more likely a conflict.
2960 In particular, don't unconditionally declare @code{malloc} or
2963 Most GNU programs use those functions just once, in functions
2964 conventionally named @code{xmalloc} and @code{xrealloc}. These
2965 functions call @code{malloc} and @code{realloc}, respectively, and
2968 Because @code{xmalloc} and @code{xrealloc} are defined in your program,
2969 you can declare them in other files without any risk of type conflict.
2971 On most systems, @code{int} is the same length as a pointer; thus, the
2972 calls to @code{malloc} and @code{realloc} work fine. For the few
2973 exceptional systems (mostly 64-bit machines), you can use
2974 @strong{conditionalized} declarations of @code{malloc} and
2975 @code{realloc}---or put these declarations in configuration files
2976 specific to those systems.
2978 @cindex string library functions
2980 The string functions require special treatment. Some Unix systems have
2981 a header file @file{string.h}; others have @file{strings.h}. Neither
2982 file name is portable. There are two things you can do: use Autoconf to
2983 figure out which file to include, or don't include either file.
2986 If you don't include either strings file, you can't get declarations for
2987 the string functions from the header file in the usual way.
2989 That causes less of a problem than you might think. The newer standard
2990 string functions should be avoided anyway because many systems still
2991 don't support them. The string functions you can use are these:
2994 strcpy strncpy strcat strncat
2995 strlen strcmp strncmp
2999 The copy and concatenate functions work fine without a declaration as
3000 long as you don't use their values. Using their values without a
3001 declaration fails on systems where the width of a pointer differs from
3002 the width of @code{int}, and perhaps in other cases. It is trivial to
3003 avoid using their values, so do that.
3005 The compare functions and @code{strlen} work fine without a declaration
3006 on most systems, possibly all the ones that GNU software runs on.
3007 You may find it necessary to declare them @strong{conditionally} on a
3010 The search functions must be declared to return @code{char *}. Luckily,
3011 there is no variation in the data type they return. But there is
3012 variation in their names. Some systems give these functions the names
3013 @code{index} and @code{rindex}; other systems use the names
3014 @code{strchr} and @code{strrchr}. Some systems support both pairs of
3015 names, but neither pair works on all systems.
3017 You should pick a single pair of names and use it throughout your
3018 program. (Nowadays, it is better to choose @code{strchr} and
3019 @code{strrchr} for new programs, since those are the standard
3020 names.) Declare both of those names as functions returning @code{char
3021 *}. On systems which don't support those names, define them as macros
3022 in terms of the other pair. For example, here is what to put at the
3023 beginning of your file (or in a header) if you want to use the names
3024 @code{strchr} and @code{strrchr} throughout:
3028 #define strchr index
3030 #ifndef HAVE_STRRCHR
3031 #define strrchr rindex
3039 Here we assume that @code{HAVE_STRCHR} and @code{HAVE_STRRCHR} are
3040 macros defined in systems where the corresponding functions exist.
3041 One way to get them properly defined is to use Autoconf.
3043 @node Internationalization
3044 @section Internationalization
3045 @cindex internationalization
3048 GNU has a library called GNU gettext that makes it easy to translate the
3049 messages in a program into various languages. You should use this
3050 library in every program. Use English for the messages as they appear
3051 in the program, and let gettext provide the way to translate them into
3054 Using GNU gettext involves putting a call to the @code{gettext} macro
3055 around each string that might need translation---like this:
3058 printf (gettext ("Processing file `%s'..."));
3062 This permits GNU gettext to replace the string @code{"Processing file
3063 `%s'..."} with a translated version.
3065 Once a program uses gettext, please make a point of writing calls to
3066 @code{gettext} when you add new strings that call for translation.
3068 Using GNU gettext in a package involves specifying a @dfn{text domain
3069 name} for the package. The text domain name is used to separate the
3070 translations for this package from the translations for other packages.
3071 Normally, the text domain name should be the same as the name of the
3072 package---for example, @samp{coreutils} for the GNU core utilities.
3074 @cindex message text, and internationalization
3075 To enable gettext to work well, avoid writing code that makes
3076 assumptions about the structure of words or sentences. When you want
3077 the precise text of a sentence to vary depending on the data, use two or
3078 more alternative string constants each containing a complete sentences,
3079 rather than inserting conditionalized words or phrases into a single
3082 Here is an example of what not to do:
3085 printf ("%s is full", capacity > 5000000 ? "disk" : "floppy disk");
3088 If you apply gettext to all strings, like this,
3091 printf (gettext ("%s is full"),
3092 capacity > 5000000 ? gettext ("disk") : gettext ("floppy disk"));
3096 the translator will hardly know that "disk" and "floppy disk" are meant to
3097 be substituted in the other string. Worse, in some languages (like French)
3098 the construction will not work: the translation of the word "full" depends
3099 on the gender of the first part of the sentence; it happens to be not the
3100 same for "disk" as for "floppy disk".
3102 Complete sentences can be translated without problems:
3105 printf (capacity > 5000000 ? gettext ("disk is full")
3106 : gettext ("floppy disk is full"));
3109 A similar problem appears at the level of sentence structure with this
3113 printf ("# Implicit rule search has%s been done.\n",
3114 f->tried_implicit ? "" : " not");
3118 Adding @code{gettext} calls to this code cannot give correct results for
3119 all languages, because negation in some languages requires adding words
3120 at more than one place in the sentence. By contrast, adding
3121 @code{gettext} calls does the job straightforwardly if the code starts
3125 printf (f->tried_implicit
3126 ? "# Implicit rule search has been done.\n",
3127 : "# Implicit rule search has not been done.\n");
3130 Another example is this one:
3133 printf ("%d file%s processed", nfiles,
3134 nfiles != 1 ? "s" : "");
3138 The problem with this example is that it assumes that plurals are made
3139 by adding `s'. If you apply gettext to the format string, like this,
3142 printf (gettext ("%d file%s processed"), nfiles,
3143 nfiles != 1 ? "s" : "");
3147 the message can use different words, but it will still be forced to use
3148 `s' for the plural. Here is a better way, with gettext being applied to
3149 the two strings independently:
3152 printf ((nfiles != 1 ? gettext ("%d files processed")
3153 : gettext ("%d file processed")),
3158 But this still doesn't work for languages like Polish, which has three
3159 plural forms: one for nfiles == 1, one for nfiles == 2, 3, 4, 22, 23, 24, ...
3160 and one for the rest. The GNU @code{ngettext} function solves this problem:
3163 printf (ngettext ("%d files processed", "%d file processed", nfiles),
3169 @section Character Set
3170 @cindex character set
3172 @cindex ASCII characters
3173 @cindex non-ASCII characters
3175 Sticking to the ASCII character set (plain text, 7-bit characters) is
3176 preferred in GNU source code comments, text documents, and other
3177 contexts, unless there is good reason to do something else because of
3178 the application domain. For example, if source code deals with the
3179 French Revolutionary calendar, it is OK if its literal strings contain
3180 accented characters in month names like ``Flor@'eal''. Also, it is OK
3181 to use non-ASCII characters to represent proper names of contributors in
3182 change logs (@pxref{Change Logs}).
3184 If you need to use non-ASCII characters, you should normally stick with
3185 one encoding, as one cannot in general mix encodings reliably.
3188 @node Quote Characters
3189 @section Quote Characters
3190 @cindex quote characters
3191 @cindex locale-specific quote characters
3193 @cindex grave accent
3195 In the C locale, GNU programs should stick to plain ASCII for quotation
3196 characters in messages to users: preferably 0x60 (@samp{`}) for left
3197 quotes and 0x27 (@samp{'}) for right quotes. It is ok, but not
3198 required, to use locale-specific quotes in other locales.
3200 The @uref{http://www.gnu.org/software/gnulib/, Gnulib} @code{quote} and
3201 @code{quotearg} modules provide a reasonably straightforward way to
3202 support locale-specific quote characters, as well as taking care of
3203 other issues, such as quoting a filename that itself contains a quote
3204 character. See the Gnulib documentation for usage details.
3206 In any case, the documentation for your program should clearly specify
3207 how it does quoting, if different than the preferred method of @samp{`}
3208 and @samp{'}. This is especially important if the output of your
3209 program is ever likely to be parsed by another program.
3211 Quotation characters are a difficult area in the computing world at
3212 this time: there are no true left or right quote characters in Latin1;
3213 the @samp{`} character we use was standardized there as a grave
3214 accent. Moreover, Latin1 is still not universally usable.
3216 Unicode contains the unambiguous quote characters required, and its
3217 common encoding UTF-8 is upward compatible with Latin1. However,
3218 Unicode and UTF-8 are not universally well-supported, either.
3220 This may change over the next few years, and then we will revisit
3228 Don't assume that @code{mmap} either works on all files or fails
3229 for all files. It may work on some files and fail on others.
3231 The proper way to use @code{mmap} is to try it on the specific file for
3232 which you want to use it---and if @code{mmap} doesn't work, fall back on
3233 doing the job in another way using @code{read} and @code{write}.
3235 The reason this precaution is needed is that the GNU kernel (the HURD)
3236 provides a user-extensible file system, in which there can be many
3237 different kinds of ``ordinary files.'' Many of them support
3238 @code{mmap}, but some do not. It is important to make programs handle
3239 all these kinds of files.
3242 @chapter Documenting Programs
3243 @cindex documentation
3245 A GNU program should ideally come with full free documentation, adequate
3246 for both reference and tutorial purposes. If the package can be
3247 programmed or extended, the documentation should cover programming or
3248 extending it, as well as just using it.
3251 * GNU Manuals:: Writing proper manuals.
3252 * Doc Strings and Manuals:: Compiling doc strings doesn't make a manual.
3253 * Manual Structure Details:: Specific structure conventions.
3254 * License for Manuals:: Writing the distribution terms for a manual.
3255 * Manual Credits:: Giving credit to documentation contributors.
3256 * Printed Manuals:: Mentioning the printed manual.
3257 * NEWS File:: NEWS files supplement manuals.
3258 * Change Logs:: Recording changes.
3259 * Man Pages:: Man pages are secondary.
3260 * Reading other Manuals:: How far you can go in learning
3265 @section GNU Manuals
3267 The preferred document format for the GNU system is the Texinfo
3268 formatting language. Every GNU package should (ideally) have
3269 documentation in Texinfo both for reference and for learners. Texinfo
3270 makes it possible to produce a good quality formatted book, using
3271 @TeX{}, and to generate an Info file. It is also possible to generate
3272 HTML output from Texinfo source. See the Texinfo manual, either the
3273 hardcopy, or the on-line version available through @code{info} or the
3274 Emacs Info subsystem (@kbd{C-h i}).
3276 Nowadays some other formats such as Docbook and Sgmltexi can be
3277 converted automatically into Texinfo. It is ok to produce the Texinfo
3278 documentation by conversion this way, as long as it gives good results.
3280 Make sure your manual is clear to a reader who knows nothing about the
3281 topic and reads it straight through. This means covering basic topics
3282 at the beginning, and advanced topics only later. This also means
3283 defining every specialized term when it is first used.
3285 Programmers tend to carry over the structure of the program as the
3286 structure for its documentation. But this structure is not
3287 necessarily good for explaining how to use the program; it may be
3288 irrelevant and confusing for a user.
3290 Instead, the right way to structure documentation is according to the
3291 concepts and questions that a user will have in mind when reading it.
3292 This principle applies at every level, from the lowest (ordering
3293 sentences in a paragraph) to the highest (ordering of chapter topics
3294 within the manual). Sometimes this structure of ideas matches the
3295 structure of the implementation of the software being documented---but
3296 often they are different. An important part of learning to write good
3297 documentation is to learn to notice when you have unthinkingly
3298 structured the documentation like the implementation, stop yourself,
3299 and look for better alternatives.
3301 For example, each program in the GNU system probably ought to be
3302 documented in one manual; but this does not mean each program should
3303 have its own manual. That would be following the structure of the
3304 implementation, rather than the structure that helps the user
3307 Instead, each manual should cover a coherent @emph{topic}. For example,
3308 instead of a manual for @code{diff} and a manual for @code{diff3}, we
3309 have one manual for ``comparison of files'' which covers both of those
3310 programs, as well as @code{cmp}. By documenting these programs
3311 together, we can make the whole subject clearer.
3313 The manual which discusses a program should certainly document all of
3314 the program's command-line options and all of its commands. It should
3315 give examples of their use. But don't organize the manual as a list
3316 of features. Instead, organize it logically, by subtopics. Address
3317 the questions that a user will ask when thinking about the job that
3318 the program does. Don't just tell the reader what each feature can
3319 do---say what jobs it is good for, and show how to use it for those
3320 jobs. Explain what is recommended usage, and what kinds of usage
3323 In general, a GNU manual should serve both as tutorial and reference.
3324 It should be set up for convenient access to each topic through Info,
3325 and for reading straight through (appendixes aside). A GNU manual
3326 should give a good introduction to a beginner reading through from the
3327 start, and should also provide all the details that hackers want.
3328 The Bison manual is a good example of this---please take a look at it
3329 to see what we mean.
3331 That is not as hard as it first sounds. Arrange each chapter as a
3332 logical breakdown of its topic, but order the sections, and write their
3333 text, so that reading the chapter straight through makes sense. Do
3334 likewise when structuring the book into chapters, and when structuring a
3335 section into paragraphs. The watchword is, @emph{at each point, address
3336 the most fundamental and important issue raised by the preceding text.}
3338 If necessary, add extra chapters at the beginning of the manual which
3339 are purely tutorial and cover the basics of the subject. These provide
3340 the framework for a beginner to understand the rest of the manual. The
3341 Bison manual provides a good example of how to do this.
3343 To serve as a reference, a manual should have an Index that list all the
3344 functions, variables, options, and important concepts that are part of
3345 the program. One combined Index should do for a short manual, but
3346 sometimes for a complex package it is better to use multiple indices.
3347 The Texinfo manual includes advice on preparing good index entries, see
3348 @ref{Index Entries, , Making Index Entries, texinfo, GNU Texinfo}, and
3349 see @ref{Indexing Commands, , Defining the Entries of an
3350 Index, texinfo, GNU Texinfo}.
3352 Don't use Unix man pages as a model for how to write GNU documentation;
3353 most of them are terse, badly structured, and give inadequate
3354 explanation of the underlying concepts. (There are, of course, some
3355 exceptions.) Also, Unix man pages use a particular format which is
3356 different from what we use in GNU manuals.
3358 Please include an email address in the manual for where to report
3359 bugs @emph{in the text of the manual}.
3361 Please do not use the term ``pathname'' that is used in Unix
3362 documentation; use ``file name'' (two words) instead. We use the term
3363 ``path'' only for search paths, which are lists of directory names.
3365 Please do not use the term ``illegal'' to refer to erroneous input to
3366 a computer program. Please use ``invalid'' for this, and reserve the
3367 term ``illegal'' for activities prohibited by law.
3369 Please do not write @samp{()} after a function name just to indicate
3370 it is a function. @code{foo ()} is not a function, it is a function
3371 call with no arguments.
3373 @node Doc Strings and Manuals
3374 @section Doc Strings and Manuals
3376 Some programming systems, such as Emacs, provide a documentation string
3377 for each function, command or variable. You may be tempted to write a
3378 reference manual by compiling the documentation strings and writing a
3379 little additional text to go around them---but you must not do it. That
3380 approach is a fundamental mistake. The text of well-written
3381 documentation strings will be entirely wrong for a manual.
3383 A documentation string needs to stand alone---when it appears on the
3384 screen, there will be no other text to introduce or explain it.
3385 Meanwhile, it can be rather informal in style.
3387 The text describing a function or variable in a manual must not stand
3388 alone; it appears in the context of a section or subsection. Other text
3389 at the beginning of the section should explain some of the concepts, and
3390 should often make some general points that apply to several functions or
3391 variables. The previous descriptions of functions and variables in the
3392 section will also have given information about the topic. A description
3393 written to stand alone would repeat some of that information; this
3394 redundancy looks bad. Meanwhile, the informality that is acceptable in
3395 a documentation string is totally unacceptable in a manual.
3397 The only good way to use documentation strings in writing a good manual
3398 is to use them as a source of information for writing good text.
3400 @node Manual Structure Details
3401 @section Manual Structure Details
3402 @cindex manual structure
3404 The title page of the manual should state the version of the programs or
3405 packages documented in the manual. The Top node of the manual should
3406 also contain this information. If the manual is changing more
3407 frequently than or independent of the program, also state a version
3408 number for the manual in both of these places.
3410 Each program documented in the manual should have a node named
3411 @samp{@var{program} Invocation} or @samp{Invoking @var{program}}. This
3412 node (together with its subnodes, if any) should describe the program's
3413 command line arguments and how to run it (the sort of information people
3414 would look for in a man page). Start with an @samp{@@example}
3415 containing a template for all the options and arguments that the program
3418 Alternatively, put a menu item in some menu whose item name fits one of
3419 the above patterns. This identifies the node which that item points to
3420 as the node for this purpose, regardless of the node's actual name.
3422 The @samp{--usage} feature of the Info reader looks for such a node
3423 or menu item in order to find the relevant text, so it is essential
3424 for every Texinfo file to have one.
3426 If one manual describes several programs, it should have such a node for
3427 each program described in the manual.
3429 @node License for Manuals
3430 @section License for Manuals
3431 @cindex license for manuals
3433 Please use the GNU Free Documentation License for all GNU manuals that
3434 are more than a few pages long. Likewise for a collection of short
3435 documents---you only need one copy of the GNU FDL for the whole
3436 collection. For a single short document, you can use a very permissive
3437 non-copyleft license, to avoid taking up space with a long license.
3439 See @uref{http://www.gnu.org/copyleft/fdl-howto.html} for more explanation
3440 of how to employ the GFDL.
3442 Note that it is not obligatory to include a copy of the GNU GPL or GNU
3443 LGPL in a manual whose license is neither the GPL nor the LGPL. It can
3444 be a good idea to include the program's license in a large manual; in a
3445 short manual, whose size would be increased considerably by including
3446 the program's license, it is probably better not to include it.
3448 @node Manual Credits
3449 @section Manual Credits
3450 @cindex credits for manuals
3452 Please credit the principal human writers of the manual as the authors,
3453 on the title page of the manual. If a company sponsored the work, thank
3454 the company in a suitable place in the manual, but do not cite the
3455 company as an author.
3457 @node Printed Manuals
3458 @section Printed Manuals
3460 The FSF publishes some GNU manuals in printed form. To encourage sales
3461 of these manuals, the on-line versions of the manual should mention at
3462 the very start that the printed manual is available and should point at
3463 information for getting it---for instance, with a link to the page
3464 @url{http://www.gnu.org/order/order.html}. This should not be included
3465 in the printed manual, though, because there it is redundant.
3467 It is also useful to explain in the on-line forms of the manual how the
3468 user can print out the manual from the sources.
3471 @section The NEWS File
3472 @cindex @file{NEWS} file
3474 In addition to its manual, the package should have a file named
3475 @file{NEWS} which contains a list of user-visible changes worth
3476 mentioning. In each new release, add items to the front of the file and
3477 identify the version they pertain to. Don't discard old items; leave
3478 them in the file after the newer items. This way, a user upgrading from
3479 any previous version can see what is new.
3481 If the @file{NEWS} file gets very long, move some of the older items
3482 into a file named @file{ONEWS} and put a note at the end referring the
3486 @section Change Logs
3489 Keep a change log to describe all the changes made to program source
3490 files. The purpose of this is so that people investigating bugs in the
3491 future will know about the changes that might have introduced the bug.
3492 Often a new bug can be found by looking at what was recently changed.
3493 More importantly, change logs can help you eliminate conceptual
3494 inconsistencies between different parts of a program, by giving you a
3495 history of how the conflicting concepts arose and who they came from.
3498 * Change Log Concepts::
3499 * Style of Change Logs::
3501 * Conditional Changes::
3502 * Indicating the Part Changed::
3505 @node Change Log Concepts
3506 @subsection Change Log Concepts
3508 You can think of the change log as a conceptual ``undo list'' which
3509 explains how earlier versions were different from the current version.
3510 People can see the current version; they don't need the change log
3511 to tell them what is in it. What they want from a change log is a
3512 clear explanation of how the earlier version differed.
3514 The change log file is normally called @file{ChangeLog} and covers an
3515 entire directory. Each directory can have its own change log, or a
3516 directory can use the change log of its parent directory--it's up to
3519 Another alternative is to record change log information with a version
3520 control system such as RCS or CVS. This can be converted automatically
3521 to a @file{ChangeLog} file using @code{rcs2log}; in Emacs, the command
3522 @kbd{C-x v a} (@code{vc-update-change-log}) does the job.
3524 There's no need to describe the full purpose of the changes or how they
3525 work together. If you think that a change calls for explanation, you're
3526 probably right. Please do explain it---but please put the explanation
3527 in comments in the code, where people will see it whenever they see the
3528 code. For example, ``New function'' is enough for the change log when
3529 you add a function, because there should be a comment before the
3530 function definition to explain what it does.
3532 In the past, we recommended not mentioning changes in non-software
3533 files (manuals, help files, etc.) in change logs. However, we've been
3534 advised that it is a good idea to include them, for the sake of
3537 However, sometimes it is useful to write one line to describe the
3538 overall purpose of a batch of changes.
3540 The easiest way to add an entry to @file{ChangeLog} is with the Emacs
3541 command @kbd{M-x add-change-log-entry}. An entry should have an
3542 asterisk, the name of the changed file, and then in parentheses the name
3543 of the changed functions, variables or whatever, followed by a colon.
3544 Then describe the changes you made to that function or variable.
3546 @node Style of Change Logs
3547 @subsection Style of Change Logs
3548 @cindex change logs, style
3550 Here are some simple examples of change log entries, starting with the
3551 header line that says who made the change and when it was installed,
3552 followed by descriptions of specific changes. (These examples are
3553 drawn from Emacs and GCC.)
3556 1998-08-17 Richard Stallman <rms@@gnu.org>
3558 * register.el (insert-register): Return nil.
3559 (jump-to-register): Likewise.
3561 * sort.el (sort-subr): Return nil.
3563 * tex-mode.el (tex-bibtex-file, tex-file, tex-region):
3564 Restart the tex shell if process is gone or stopped.
3565 (tex-shell-running): New function.
3567 * expr.c (store_one_arg): Round size up for move_block_to_reg.
3568 (expand_call): Round up when emitting USE insns.
3569 * stmt.c (assign_parms): Round size up for move_block_from_reg.
3572 It's important to name the changed function or variable in full. Don't
3573 abbreviate function or variable names, and don't combine them.
3574 Subsequent maintainers will often search for a function name to find all
3575 the change log entries that pertain to it; if you abbreviate the name,
3576 they won't find it when they search.
3578 For example, some people are tempted to abbreviate groups of function
3579 names by writing @samp{* register.el (@{insert,jump-to@}-register)};
3580 this is not a good idea, since searching for @code{jump-to-register} or
3581 @code{insert-register} would not find that entry.
3583 Separate unrelated change log entries with blank lines. When two
3584 entries represent parts of the same change, so that they work together,
3585 then don't put blank lines between them. Then you can omit the file
3586 name and the asterisk when successive entries are in the same file.
3588 Break long lists of function names by closing continued lines with
3589 @samp{)}, rather than @samp{,}, and opening the continuation with
3590 @samp{(} as in this example:
3593 * keyboard.c (menu_bar_items, tool_bar_items)
3594 (Fexecute_extended_command): Deal with `keymap' property.
3597 When you install someone else's changes, put the contributor's name in
3598 the change log entry rather than in the text of the entry. In other
3602 2002-07-14 John Doe <jdoe@@gnu.org>
3604 * sewing.c: Make it sew.
3611 2002-07-14 Usual Maintainer <usual@@gnu.org>
3613 * sewing.c: Make it sew. Patch by jdoe@@gnu.org.
3616 As for the date, that should be the date you applied the change.
3618 @node Simple Changes
3619 @subsection Simple Changes
3621 Certain simple kinds of changes don't need much detail in the change
3624 When you change the calling sequence of a function in a simple fashion,
3625 and you change all the callers of the function to use the new calling
3626 sequence, there is no need to make individual entries for all the
3627 callers that you changed. Just write in the entry for the function
3628 being called, ``All callers changed''---like this:
3631 * keyboard.c (Fcommand_execute): New arg SPECIAL.
3632 All callers changed.
3635 When you change just comments or doc strings, it is enough to write an
3636 entry for the file, without mentioning the functions. Just ``Doc
3637 fixes'' is enough for the change log.
3639 There's no technical need to make change log entries for documentation
3640 files. This is because documentation is not susceptible to bugs that
3641 are hard to fix. Documentation does not consist of parts that must
3642 interact in a precisely engineered fashion. To correct an error, you
3643 need not know the history of the erroneous passage; it is enough to
3644 compare what the documentation says with the way the program actually
3647 However, you should keep change logs for documentation files when the
3648 project gets copyright assignments from its contributors, so as to
3649 make the records of authorship more accurate.
3651 @node Conditional Changes
3652 @subsection Conditional Changes
3653 @cindex conditional changes, and change logs
3654 @cindex change logs, conditional changes
3656 C programs often contain compile-time @code{#if} conditionals. Many
3657 changes are conditional; sometimes you add a new definition which is
3658 entirely contained in a conditional. It is very useful to indicate in
3659 the change log the conditions for which the change applies.
3661 Our convention for indicating conditional changes is to use square
3662 brackets around the name of the condition.
3664 Here is a simple example, describing a change which is conditional but
3665 does not have a function or entity name associated with it:
3668 * xterm.c [SOLARIS2]: Include string.h.
3671 Here is an entry describing a new definition which is entirely
3672 conditional. This new definition for the macro @code{FRAME_WINDOW_P} is
3673 used only when @code{HAVE_X_WINDOWS} is defined:
3676 * frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined.
3679 Here is an entry for a change within the function @code{init_display},
3680 whose definition as a whole is unconditional, but the changes themselves
3681 are contained in a @samp{#ifdef HAVE_LIBNCURSES} conditional:
3684 * dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent.
3687 Here is an entry for a change that takes affect only when
3688 a certain macro is @emph{not} defined:
3691 (gethostname) [!HAVE_SOCKETS]: Replace with winsock version.
3694 @node Indicating the Part Changed
3695 @subsection Indicating the Part Changed
3697 Indicate the part of a function which changed by using angle brackets
3698 enclosing an indication of what the changed part does. Here is an entry
3699 for a change in the part of the function @code{sh-while-getopts} that
3700 deals with @code{sh} commands:
3703 * progmodes/sh-script.el (sh-while-getopts) <sh>: Handle case that
3704 user-specified option string is empty.
3712 In the GNU project, man pages are secondary. It is not necessary or
3713 expected for every GNU program to have a man page, but some of them do.
3714 It's your choice whether to include a man page in your program.
3716 When you make this decision, consider that supporting a man page
3717 requires continual effort each time the program is changed. The time
3718 you spend on the man page is time taken away from more useful work.
3720 For a simple program which changes little, updating the man page may be
3721 a small job. Then there is little reason not to include a man page, if
3724 For a large program that changes a great deal, updating a man page may
3725 be a substantial burden. If a user offers to donate a man page, you may
3726 find this gift costly to accept. It may be better to refuse the man
3727 page unless the same person agrees to take full responsibility for
3728 maintaining it---so that you can wash your hands of it entirely. If
3729 this volunteer later ceases to do the job, then don't feel obliged to
3730 pick it up yourself; it may be better to withdraw the man page from the
3731 distribution until someone else agrees to update it.
3733 When a program changes only a little, you may feel that the
3734 discrepancies are small enough that the man page remains useful without
3735 updating. If so, put a prominent note near the beginning of the man
3736 page explaining that you don't maintain it and that the Texinfo manual
3737 is more authoritative. The note should say how to access the Texinfo
3740 Be sure that man pages include a copyright statement and free
3741 license. The simple all-permissive license is appropriate for simple
3745 Copying and distribution of this file, with or without modification,
3746 are permitted in any medium without royalty provided the copyright
3747 notice and this notice are preserved.
3750 For long man pages, with enough explanation and documentation that
3751 they can be considered true manuals, use the GFDL (@pxref{License for
3754 Finally, the GNU help2man program
3755 (@uref{http://www.gnu.org/software/help2man/}) is one way to automate
3756 generation of a man page, in this case from @option{--help} output.
3757 This is sufficient in many cases.
3759 @node Reading other Manuals
3760 @section Reading other Manuals
3762 There may be non-free books or documentation files that describe the
3763 program you are documenting.
3765 It is ok to use these documents for reference, just as the author of a
3766 new algebra textbook can read other books on algebra. A large portion
3767 of any non-fiction book consists of facts, in this case facts about how
3768 a certain program works, and these facts are necessarily the same for
3769 everyone who writes about the subject. But be careful not to copy your
3770 outline structure, wording, tables or examples from preexisting non-free
3771 documentation. Copying from free documentation may be ok; please check
3772 with the FSF about the individual case.
3774 @node Managing Releases
3775 @chapter The Release Process
3778 Making a release is more than just bundling up your source files in a
3779 tar file and putting it up for FTP. You should set up your software so
3780 that it can be configured to run on a variety of systems. Your Makefile
3781 should conform to the GNU standards described below, and your directory
3782 layout should also conform to the standards discussed below. Doing so
3783 makes it easy to include your package into the larger framework of
3787 * Configuration:: How configuration of GNU packages should work.
3788 * Makefile Conventions:: Makefile conventions.
3789 * Releases:: Making releases
3793 @section How Configuration Should Work
3794 @cindex program configuration
3797 Each GNU distribution should come with a shell script named
3798 @code{configure}. This script is given arguments which describe the
3799 kind of machine and system you want to compile the program for.
3800 The @code{configure} script must record the configuration options so
3801 that they affect compilation.
3803 The description here is the specification of the interface for the
3804 @code{configure} script in GNU packages. Many packages implement it
3805 using GNU Autoconf (@pxref{Top,, Introduction, autoconf, Autoconf})
3806 and/or GNU Automake (@pxref{Top,, Introduction, automake, Automake}),
3807 but you do not have to use these tools. You can implement it any way
3808 you like; for instance, by making @code{configure} be a wrapper around
3809 a completely different configuration system.
3811 Another way for the @code{configure} script to operate is to make a
3812 link from a standard name such as @file{config.h} to the proper
3813 configuration file for the chosen system. If you use this technique,
3814 the distribution should @emph{not} contain a file named
3815 @file{config.h}. This is so that people won't be able to build the
3816 program without configuring it first.
3818 Another thing that @code{configure} can do is to edit the Makefile. If
3819 you do this, the distribution should @emph{not} contain a file named
3820 @file{Makefile}. Instead, it should include a file @file{Makefile.in} which
3821 contains the input used for editing. Once again, this is so that people
3822 won't be able to build the program without configuring it first.
3824 If @code{configure} does write the @file{Makefile}, then @file{Makefile}
3825 should have a target named @file{Makefile} which causes @code{configure}
3826 to be rerun, setting up the same configuration that was set up last
3827 time. The files that @code{configure} reads should be listed as
3828 dependencies of @file{Makefile}.
3830 All the files which are output from the @code{configure} script should
3831 have comments at the beginning explaining that they were generated
3832 automatically using @code{configure}. This is so that users won't think
3833 of trying to edit them by hand.
3835 The @code{configure} script should write a file named @file{config.status}
3836 which describes which configuration options were specified when the
3837 program was last configured. This file should be a shell script which,
3838 if run, will recreate the same configuration.
3840 The @code{configure} script should accept an option of the form
3841 @samp{--srcdir=@var{dirname}} to specify the directory where sources are found
3842 (if it is not the current directory). This makes it possible to build
3843 the program in a separate directory, so that the actual source directory
3846 If the user does not specify @samp{--srcdir}, then @code{configure} should
3847 check both @file{.} and @file{..} to see if it can find the sources. If
3848 it finds the sources in one of these places, it should use them from
3849 there. Otherwise, it should report that it cannot find the sources, and
3850 should exit with nonzero status.
3852 Usually the easy way to support @samp{--srcdir} is by editing a
3853 definition of @code{VPATH} into the Makefile. Some rules may need to
3854 refer explicitly to the specified source directory. To make this
3855 possible, @code{configure} can add to the Makefile a variable named
3856 @code{srcdir} whose value is precisely the specified directory.
3858 In addition, the @samp{configure} script should take options
3859 corresponding to most of the standard directory variables
3860 (@pxref{Directory Variables}). Here is the list:
3863 --prefix --exec-prefix --bindir --sbindir --libexecdir --sysconfdir
3864 --sharedstatedir --localstatedir --libdir --includedir --oldincludedir
3865 --datarootdir --datadir --infodir --localedir --mandir --docdir
3866 --htmldir --dvidir --pdfdir --psdir
3869 The @code{configure} script should also take an argument which specifies the
3870 type of system to build the program for. This argument should look like
3874 @var{cpu}-@var{company}-@var{system}
3877 For example, an Athlon-based GNU/Linux system might be
3878 @samp{i686-pc-linux-gnu}.
3880 The @code{configure} script needs to be able to decode all plausible
3881 alternatives for how to describe a machine. Thus,
3882 @samp{athlon-pc-gnu/linux} would be a valid alias. There is a shell
3884 @uref{http://git.savannah.gnu.org/@/gitweb/@/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD,
3885 @file{config.sub}} that you can use as a subroutine to validate system
3886 types and canonicalize aliases.
3888 The @code{configure} script should also take the option
3889 @option{--build=@var{buildtype}}, which should be equivalent to a
3890 plain @var{buildtype} argument. For example, @samp{configure
3891 --build=i686-pc-linux-gnu} is equivalent to @samp{configure
3892 i686-pc-linux-gnu}. When the build type is not specified by an option
3893 or argument, the @code{configure} script should normally guess it using
3895 @uref{http://git.savannah.gnu.org/@/gitweb/@/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD,
3896 @file{config.guess}}.
3898 @cindex optional features, configure-time
3899 Other options are permitted to specify in more detail the software
3900 or hardware present on the machine, to include or exclude optional parts
3901 of the package, or to adjust the name of some tools or arguments to them:
3904 @item --enable-@var{feature}@r{[}=@var{parameter}@r{]}
3905 Configure the package to build and install an optional user-level
3906 facility called @var{feature}. This allows users to choose which
3907 optional features to include. Giving an optional @var{parameter} of
3908 @samp{no} should omit @var{feature}, if it is built by default.
3910 No @samp{--enable} option should @strong{ever} cause one feature to
3911 replace another. No @samp{--enable} option should ever substitute one
3912 useful behavior for another useful behavior. The only proper use for
3913 @samp{--enable} is for questions of whether to build part of the program
3916 @item --with-@var{package}
3917 @c @r{[}=@var{parameter}@r{]}
3918 The package @var{package} will be installed, so configure this package
3919 to work with @var{package}.
3921 @c Giving an optional @var{parameter} of
3922 @c @samp{no} should omit @var{package}, if it is used by default.
3924 Possible values of @var{package} include
3925 @samp{gnu-as} (or @samp{gas}), @samp{gnu-ld}, @samp{gnu-libc},
3931 Do not use a @samp{--with} option to specify the file name to use to
3932 find certain files. That is outside the scope of what @samp{--with}
3935 @item @var{variable}=@var{value}
3936 Set the value of the variable @var{variable} to @var{value}. This is
3937 used to override the default values of commands or arguments in the
3938 build process. For example, the user could issue @samp{configure
3939 CFLAGS=-g CXXFLAGS=-g} to build with debugging information and without
3940 the default optimization.
3942 Specifying variables as arguments to @code{configure}, like this:
3946 is preferable to setting them in environment variables:
3950 as it helps to recreate the same configuration later with
3951 @file{config.status}.
3954 All @code{configure} scripts should accept all of the ``detail''
3955 options and the variable settings, whether or not they make any
3956 difference to the particular package at hand. In particular, they
3957 should accept any option that starts with @samp{--with-} or
3958 @samp{--enable-}. This is so users will be able to configure an
3959 entire GNU source tree at once with a single set of options.
3961 You will note that the categories @samp{--with-} and @samp{--enable-}
3962 are narrow: they @strong{do not} provide a place for any sort of option
3963 you might think of. That is deliberate. We want to limit the possible
3964 configuration options in GNU software. We do not want GNU programs to
3965 have idiosyncratic configuration options.
3967 Packages that perform part of the compilation process may support
3968 cross-compilation. In such a case, the host and target machines for the
3969 program may be different.
3971 The @code{configure} script should normally treat the specified type of
3972 system as both the host and the target, thus producing a program which
3973 works for the same type of machine that it runs on.
3975 To compile a program to run on a host type that differs from the build
3976 type, use the configure option @option{--host=@var{hosttype}}, where
3977 @var{hosttype} uses the same syntax as @var{buildtype}. The host type
3978 normally defaults to the build type.
3980 To configure a cross-compiler, cross-assembler, or what have you, you
3981 should specify a target different from the host, using the configure
3982 option @samp{--target=@var{targettype}}. The syntax for
3983 @var{targettype} is the same as for the host type. So the command would
3987 ./configure --host=@var{hosttype} --target=@var{targettype}
3990 The target type normally defaults to the host type.
3991 Programs for which cross-operation is not meaningful need not accept the
3992 @samp{--target} option, because configuring an entire operating system for
3993 cross-operation is not a meaningful operation.
3995 Some programs have ways of configuring themselves automatically. If
3996 your program is set up to do this, your @code{configure} script can simply
3997 ignore most of its arguments.
3999 @comment The makefile standards are in a separate file that is also
4000 @comment included by make.texinfo. Done by roland@gnu.ai.mit.edu on 1/6/93.
4001 @comment For this document, turn chapters into sections, etc.
4003 @include make-stds.texi
4007 @section Making Releases
4010 You should identify each release with a pair of version numbers, a
4011 major version and a minor. We have no objection to using more than
4012 two numbers, but it is very unlikely that you really need them.
4014 Package the distribution of @code{Foo version 69.96} up in a gzipped tar
4015 file with the name @file{foo-69.96.tar.gz}. It should unpack into a
4016 subdirectory named @file{foo-69.96}.
4018 Building and installing the program should never modify any of the files
4019 contained in the distribution. This means that all the files that form
4020 part of the program in any way must be classified into @dfn{source
4021 files} and @dfn{non-source files}. Source files are written by humans
4022 and never changed automatically; non-source files are produced from
4023 source files by programs under the control of the Makefile.
4025 @cindex @file{README} file
4026 The distribution should contain a file named @file{README} which gives
4027 the name of the package, and a general description of what it does. It
4028 is also good to explain the purpose of each of the first-level
4029 subdirectories in the package, if there are any. The @file{README} file
4030 should either state the version number of the package, or refer to where
4031 in the package it can be found.
4033 The @file{README} file should refer to the file @file{INSTALL}, which
4034 should contain an explanation of the installation procedure.
4036 The @file{README} file should also refer to the file which contains the
4037 copying conditions. The GNU GPL, if used, should be in a file called
4038 @file{COPYING}. If the GNU LGPL is used, it should be in a file called
4041 Naturally, all the source files must be in the distribution. It is okay
4042 to include non-source files in the distribution, provided they are
4043 up-to-date and machine-independent, so that building the distribution
4044 normally will never modify them. We commonly include non-source files
4045 produced by Bison, @code{lex}, @TeX{}, and @code{makeinfo}; this helps avoid
4046 unnecessary dependencies between our distributions, so that users can
4047 install whichever packages they want to install.
4049 Non-source files that might actually be modified by building and
4050 installing the program should @strong{never} be included in the
4051 distribution. So if you do distribute non-source files, always make
4052 sure they are up to date when you make a new distribution.
4054 Make sure that the directory into which the distribution unpacks (as
4055 well as any subdirectories) are all world-writable (octal mode 777).
4056 This is so that old versions of @code{tar} which preserve the
4057 ownership and permissions of the files from the tar archive will be
4058 able to extract all the files even if the user is unprivileged.
4060 Make sure that all the files in the distribution are world-readable.
4062 Don't include any symbolic links in the distribution itself. If the tar
4063 file contains symbolic links, then people cannot even unpack it on
4064 systems that don't support symbolic links. Also, don't use multiple
4065 names for one file in different directories, because certain file
4066 systems cannot handle this and that prevents unpacking the
4069 Try to make sure that all the file names will be unique on MS-DOS. A
4070 name on MS-DOS consists of up to 8 characters, optionally followed by a
4071 period and up to three characters. MS-DOS will truncate extra
4072 characters both before and after the period. Thus,
4073 @file{foobarhacker.c} and @file{foobarhacker.o} are not ambiguous; they
4074 are truncated to @file{foobarha.c} and @file{foobarha.o}, which are
4077 @cindex @file{texinfo.tex}, in a distribution
4078 Include in your distribution a copy of the @file{texinfo.tex} you used
4079 to test print any @file{*.texinfo} or @file{*.texi} files.
4081 Likewise, if your program uses small GNU software packages like regex,
4082 getopt, obstack, or termcap, include them in the distribution file.
4083 Leaving them out would make the distribution file a little smaller at
4084 the expense of possible inconvenience to a user who doesn't know what
4088 @chapter References to Non-Free Software and Documentation
4089 @cindex references to non-free material
4091 A GNU program should not recommend, promote, or grant legitimacy to
4092 the use of any non-free program. Proprietary software is a social and
4093 ethical problem, and our aim is to put an end to that problem. We
4094 can't stop some people from writing proprietary programs, or stop
4095 other people from using them, but we can and should refuse to
4096 advertise them to new potential customers, or to give the public the
4097 idea that their existence is ethical.
4099 The GNU definition of free software is found on the GNU web site at
4100 @url{http://www.gnu.org/@/philosophy/@/free-sw.html}, and the definition
4101 of free documentation is found at
4102 @url{http://www.gnu.org/@/philosophy/@/free-doc.html}. The terms ``free''
4103 and ``non-free'', used in this document, refer to those definitions.
4105 A list of important licenses and whether they qualify as free is in
4106 @url{http://www.gnu.org/@/licenses/@/license-list.html}. If it is not
4107 clear whether a license qualifies as free, please ask the GNU Project
4108 by writing to @email{licensing@@gnu.org}. We will answer, and if the
4109 license is an important one, we will add it to the list.
4111 When a non-free program or system is well known, you can mention it in
4112 passing---that is harmless, since users who might want to use it
4113 probably already know about it. For instance, it is fine to explain
4114 how to build your package on top of some widely used non-free
4115 operating system, or how to use it together with some widely used
4118 However, you should give only the necessary information to help those
4119 who already use the non-free program to use your program with
4120 it---don't give, or refer to, any further information about the
4121 proprietary program, and don't imply that the proprietary program
4122 enhances your program, or that its existence is in any way a good
4123 thing. The goal should be that people already using the proprietary
4124 program will get the advice they need about how to use your free
4125 program with it, while people who don't already use the proprietary
4126 program will not see anything likely to lead them to take an interest
4129 If a non-free program or system is obscure in your program's domain,
4130 your program should not mention or support it at all, since doing so
4131 would tend to popularize the non-free program more than it popularizes
4132 your program. (You cannot hope to find many additional users for your
4133 program among the users of Foobar, if the existence of Foobar is not
4134 generally known among people who might want to use your program.)
4136 Sometimes a program is free software in itself but depends on a
4137 non-free platform in order to run. For instance, many Java programs
4138 depend on some non-free Java libraries. To recommend or promote such
4139 a program is to promote the other programs it needs. This is why we
4140 are careful about listing Java programs in the Free Software
4141 Directory: we don't want to promote the non-free Java libraries.
4143 We hope this particular problem with Java will be gone by and by, as
4144 we replace the remaining non-free standard Java libraries with free
4145 software, but the general principle will remain the same: don't
4146 recommend, promote or legitimize programs that depend on non-free
4149 Some free programs strongly encourage the use of non-free software. A
4150 typical example is @command{mplayer}. It is free software in itself,
4151 and the free code can handle some kinds of files. However,
4152 @command{mplayer} recommends use of non-free codecs for other kinds of
4153 files, and users that install @command{mplayer} are very likely to
4154 install those codecs along with it. To recommend @command{mplayer}
4155 is, in effect, to promote use of the non-free codecs.
4157 Thus, you should not recommend programs that strongly encourage the
4158 use of non-free software. This is why we do not list
4159 @command{mplayer} in the Free Software Directory.
4161 A GNU package should not refer the user to any non-free documentation
4162 for free software. Free documentation that can be included in free
4163 operating systems is essential for completing the GNU system, or any
4164 free operating system, so encouraging it is a priority; to recommend
4165 use of documentation that we are not allowed to include undermines the
4166 impetus for the community to produce documentation that we can
4167 include. So GNU packages should never recommend non-free
4170 By contrast, it is ok to refer to journal articles and textbooks in
4171 the comments of a program for explanation of how it functions, even
4172 though they are non-free. This is because we don't include such
4173 things in the GNU system even they are free---they are outside the
4174 scope of what a software distribution needs to include.
4176 Referring to a web site that describes or recommends a non-free
4177 program is promoting that program, so please do not make links (or
4178 mention by name) web sites that contain such material. This policy is
4179 relevant particularly for the web pages for a GNU package.
4181 Following links from nearly any web site can lead eventually to
4182 non-free software; this is inherent in the nature of the web. So it
4183 makes no sense to criticize a site for having such links. As long as
4184 the site does not itself recommend a non-free program, there is no
4185 need to consider the question of the sites that it links to for other
4188 Thus, for example, you should not refer to AT&T's web site if that
4189 recommends AT&T's non-free software packages; you should not refer to
4190 a site that links to AT&T's site presenting it as a place to get some
4191 non-free program, because that link recommends and legitimizes the
4192 non-free program. However, that a site contains a link to AT&T's web
4193 site for some other purpose (such as long-distance telephone service)
4194 is not an objection against it.
4196 @node GNU Free Documentation License
4197 @appendix GNU Free Documentation License
4199 @cindex FDL, GNU Free Documentation License
4209 eval: (add-hook 'write-file-hooks 'time-stamp)
4210 time-stamp-start: "@set lastupdate "
4212 time-stamp-format: "%:b %:d, %:y"
4213 compile-command: "make just-standards"