@setfilename standards.info
@settitle GNU Coding Standards
@c This date is automagically updated when you save this file:
-@set lastupdate April 23, 2006
+@set lastupdate December 17, 2013
@c %**end of header
@dircategory GNU organization
@direntry
-* Standards: (standards). GNU coding standards.
+* Standards: (standards). GNU coding standards.
@end direntry
@c @setchapternewpage odd
@c This is used by a cross ref in make-stds.texi
@set CODESTD 1
-@iftex
-@set CHAPTER chapter
-@end iftex
-@ifinfo
-@set CHAPTER node
-@end ifinfo
@copying
The GNU coding standards, last updated @value{lastupdate}.
-Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
-2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
+Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
+2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
+2011, 2012, 2013 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.1
-or any later version published by the Free Software Foundation;
-with no Invariant Sections, with no
-Front-Cover Texts, and with no Back-Cover Texts.
-A copy of the license is included in the section entitled ``GNU
-Free Documentation License''.
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
+Texts. A copy of the license is included in the section entitled
+``GNU Free Documentation License''.
@end copying
@titlepage
@contents
@ifnottex
-@node Top, Preface, (dir), (dir)
-@top Version
+@node Top
+@top GNU Coding Standards
@insertcopying
@end ifnottex
@menu
-* Preface:: About the GNU Coding Standards
-* Legal Issues:: Keeping Free Software Free
-* Design Advice:: General Program Design
-* Program Behavior:: Program Behavior for All Programs
-* Writing C:: Making The Best Use of C
-* Documentation:: Documenting Programs
-* Managing Releases:: The Release Process
-* References:: References to Non-Free Software or Documentation
-* Copying This Manual:: How to Make Copies of This Manual
+* Preface:: About the GNU Coding Standards.
+* Legal Issues:: Keeping free software free.
+* Design Advice:: General program design.
+* Program Behavior:: Program behavior for all programs
+* Writing C:: Making the best use of C.
+* Documentation:: Documenting programs.
+* Managing Releases:: The release process.
+* References:: Mentioning non-free software or documentation.
+* GNU Free Documentation License:: Copying and sharing this manual.
* Index::
@end menu
even if you write in another programming language. The rules often
state reasons for writing in a certain way.
-This release of the GNU Coding Standards was last updated
-@value{lastupdate}.
-
@cindex where to obtain @code{standards.texi}
@cindex downloading this manual
If you did not obtain this file directly from the GNU project and
different formats, including the Texinfo source, PDF, HTML, DVI, plain
text, and more, at: @uref{http://www.gnu.org/prep/standards/}.
-Corrections or suggestions for this document should be sent to
-@email{bug-standards@@gnu.org}. If you make a suggestion, please include a
-suggested new wording for it; our time is limited. We prefer a context
-diff to the @file{standards.texi} or @file{make-stds.texi} files, but if
-you don't have those files, please mail your suggestion anyway.
+If you are maintaining an official GNU package, in addition to this
+document, please read and follow the GNU maintainer information
+(@pxref{Top, , Contents, maintain, Information for Maintainers of GNU
+Software}).
+
+@cindex @code{gnustandards-commit@@gnu.org} mailing list
+If you want to receive diffs for every change to these GNU documents,
+join the mailing list @code{gnustandards-commit@@gnu.org}, via the web
+interface at
+@url{http://lists.gnu.org/mailman/listinfo/gnustandards-commit}.
+Archives are also available there.
+
+@cindex @code{bug-standards@@gnu.org} email address
+@cindex Savannah repository for gnustandards
+@cindex gnustandards project repository
+Please send corrections or suggestions for this document to
+@email{bug-standards@@gnu.org}. If you make a suggestion, please
+include a suggested new wording for it, to help us consider the
+suggestion efficiently. We prefer a context diff to the Texinfo
+source, but if that's difficult for you, you can make a context diff
+for some other version of this document, or propose it in any way that
+makes it clear. The source repository for this document can be found
+at @url{http://savannah.gnu.org/projects/gnustandards}.
These standards cover the minimum of what is important when writing a
-GNU package. Likely, the needs for additional standards will come up.
+GNU package. Likely, the need for additional standards will come up.
Sometimes, you might suggest that such standards be added to this
document. If you think your standards would be generally useful, please
do suggest them.
coding standards for a trivial program.
@uref{http://www.gnu.org/software/hello/hello.html}.
+This release of the GNU Coding Standards was last updated
+@value{lastupdate}.
+
+
@node Legal Issues
@chapter Keeping Free Software Free
@cindex legal aspects
avoids legal difficulties, and other related issues.
@menu
-* Reading Non-Free Code:: Referring to Proprietary Programs
-* Contributions:: Accepting Contributions
-* Trademarks:: How We Deal with Trademark Issues
+* Reading Non-Free Code:: Referring to proprietary programs.
+* Contributions:: Accepting contributions.
+* Trademarks:: How we deal with trademark issues.
@end menu
@node Reading Non-Free Code
For example, Unix utilities were generally optimized to minimize
memory use; if you go for speed instead, your program will be very
-different. You could keep the entire input file in core and scan it
+different. You could keep the entire input file in memory and scan it
there instead of using stdio. Use a smarter algorithm discovered more
recently than the Unix program. Eliminate use of temporary files. Do
it in one pass instead of two (we did this in the assembler).
Or use a simple garbage collector instead of tracking precisely when
to free memory, or use a new GNU facility such as obstacks.
+
@node Contributions
@section Accepting Contributions
@cindex legal papers
contributor. We could be very embarrassed in court some day as a
result.
-We have more detailed advice for maintainers of programs; if you have
-reached the stage of actually maintaining a program for GNU (whether
-released or not), please ask us for a copy. It is also available
-online for your perusal: @uref{http://www.gnu.org/prep/maintain/}.
+We have more detailed advice for maintainers of GNU packages. If you
+have reached the stage of maintaining a GNU program (whether released
+or not), please take a look: @pxref{Legal Matters,,, maintain,
+Information for GNU Maintainers}.
+
@node Trademarks
@section Trademarks
@menu
* Source Language:: Which languages to use.
-* Compatibility:: Compatibility with other implementations
-* Using Extensions:: Using non-standard features
-* Standard C:: Using Standard C features
-* Conditional Compilation:: Compiling Code Only If A Conditional is True
+* Compatibility:: Compatibility with other implementations.
+* Using Extensions:: Using non-standard features.
+* Standard C:: Using standard C features.
+* Conditional Compilation:: Compiling code only if a conditional is true.
@end menu
@node Source Language
@cindex programming languages
When you want to use a language that gets compiled and runs at high
-speed, the best language to use is C. Using another language is like
-using a non-standard feature: it will cause trouble for users. Even if
-GCC supports the other language, users may find it inconvenient to have
-to install the compiler for that other language in order to build your
-program. For example, if you write your program in C++, people will
-have to install the GNU C++ compiler in order to compile your program.
-
-C has one other advantage over C++ and other compiled languages: more
-people know C, so more people will find it easy to read and modify the
-program if it is written in C.
-
-So in general it is much better to use C, rather than the
-comparable alternatives.
-
-But there are two exceptions to that conclusion:
-
-@itemize @bullet
-@item
-It is no problem to use another language to write a tool specifically
-intended for use with that language. That is because the only people
-who want to build the tool will be those who have installed the other
-language anyway.
-
-@item
-If an application is of interest only to a narrow part of the community,
-then the question of which language it is written in has less effect on
-other people, so you may as well please yourself.
-@end itemize
+speed, the best language to use is C. C++ is ok too, but please don't
+make heavy use of templates. So is Java, if you compile it.
+
+When highest efficiency is not required, other languages commonly used
+in the free software community, such as Scheme, Python, Ruby, and
+Java, are OK too. Scheme, as implemented by GNU@tie{}Guile, plays a
+particular role in the GNU System: it is the preferred language to
+extend programs written in C/C++, and also a fine language for a wide
+range of applications. The more GNU components use Guile and Scheme,
+the more users are able to extend and combine them (@pxref{The Emacs
+Thesis,,, guile, GNU Guile Reference Manual}).
Many programs are designed to be extensible: they include an interpreter
for a language that is higher level than C. Often much of the program
is written in that language, too. The Emacs editor pioneered this
technique.
-@cindex GUILE
-The standard extensibility interpreter for GNU software is GUILE
-(@uref{http://www.gnu.org/software/guile/}), which implements the
-language Scheme (an especially clean and simple dialect of Lisp). We
-don't reject programs written in other ``scripting languages'' such as
-Perl and Python, but using GUILE is very important for the overall
-consistency of the GNU system.
+@cindex Guile
+@cindex GNOME and Guile
+The standard extensibility interpreter for GNU software is Guile
+(@uref{http://www.gnu.org/@/software/@/guile/}), which implements the
+language Scheme (an especially clean and simple dialect of Lisp).
+Guile also includes bindings for GTK+/GNOME, making it practical to
+write modern GUI functionality within Guile. We don't reject programs
+written in other ``scripting languages'' such as Perl and Python, but
+using Guile is the path that will lead to overall consistency of the
+GNU system.
+
@node Compatibility
@section Compatibility with Other Implementations
-@cindex compatibility with C and @sc{posix} standards
-@cindex @sc{posix} compatibility
+@cindex compatibility with C and POSIX standards
+@cindex C compatibility
+@cindex POSIX compatibility
With occasional exceptions, utility programs and libraries for GNU
should be upward compatible with those in Berkeley Unix, and upward
compatible with Standard C if Standard C specifies their
-behavior, and upward compatible with @sc{posix} if @sc{posix} specifies
+behavior, and upward compatible with POSIX if POSIX specifies
their behavior.
When these standards conflict, it is useful to offer compatibility
modes for each of them.
@cindex options for compatibility
-Standard C and @sc{posix} prohibit many kinds of extensions. Feel
+Standard C and POSIX prohibit many kinds of extensions. Feel
free to make the extensions anyway, and include a @samp{--ansi},
@samp{--posix}, or @samp{--compatible} option to turn them off.
However, if the extension has a significant chance of breaking any real
should try to redesign its interface to make it upward compatible.
@cindex @code{POSIXLY_CORRECT}, environment variable
-Many GNU programs suppress extensions that conflict with @sc{posix} if the
+Many GNU programs suppress extensions that conflict with POSIX if the
environment variable @code{POSIXLY_CORRECT} is defined (even if it is
defined with a null value). Please make your program recognize this
variable if appropriate.
@node Standard C
@section Standard C and Pre-Standard C
-@cindex @sc{ansi} C standard
+@cindex ANSI C standard
1989 Standard C is widespread enough now that it is ok to use its
-features in new programs. There is one exception: do not ever use the
+features in programs. There is one exception: do not ever use the
``trigraph'' feature of Standard C.
-1999 Standard C is not widespread yet, so please do not require its
-features in programs. It is ok to use its features if they are present.
+The 1999 and 2011 editions of Standard C are not fully supported
+on all platforms. If you aim to support compilation by
+compilers other than GCC, you should not require these C
+features in your programs. It is ok to use these features
+conditionally when the compiler supports them.
+
+If your program is only meant to compile with GCC, then you can
+use these features if GCC supports them, when they give substantial
+benefit.
However, it is easy to support pre-standard compilers in most programs,
-so if you know how to do that, feel free. If a program you are
-maintaining has such support, you should try to keep it working.
+so if you know how to do that, feel free.
@cindex function prototypes
To support pre-standard C, instead of writing function definitions in
GCC developers many hours, or even days, per year.
In the case of function-like macros like @code{REVERSIBLE_CC_MODE} in
-GCC which cannot be simply used in @code{if( ...)} statements, there is
+GCC which cannot be simply used in @code{if (...)} statements, there is
an easy workaround. Simply introduce another macro
@code{HAS_REVERSIBLE_CC_MODE} as in the following example:
@menu
* Non-GNU Standards:: We consider standards such as POSIX;
we don't "obey" them.
-* Semantics:: Writing robust programs
-* Libraries:: Library behavior
-* Errors:: Formatting error messages
-* User Interfaces:: Standards about interfaces generally
-* Graphical Interfaces:: Standards for graphical interfaces
-* Command-Line Interfaces:: Standards for command line interfaces
-* Option Table:: Table of long options
-* Memory Usage:: When and how to care about memory needs
-* File Usage:: Which files to use, and where
+* Semantics:: Writing robust programs.
+* Libraries:: Library behavior.
+* Errors:: Formatting error messages.
+* User Interfaces:: Standards about interfaces generally.
+* Graphical Interfaces:: Standards for graphical interfaces.
+* Command-Line Interfaces:: Standards for command line interfaces.
+* Dynamic Plug-In Interfaces:: Standards for dynamic plug-in interfaces.
+* Option Table:: Table of long options.
+* OID Allocations:: Table of OID slots for GNU.
+* Memory Usage:: When and how to care about memory needs.
+* File Usage:: Which files to use, and where.
@end menu
@node Non-GNU Standards
were later adopted as part of the standard. If you want these
constructs to give an error message as ``required'' by the standard,
you must specify @samp{--pedantic}, which was implemented only so that
-we can say ``GCC is a 100% implementation of the standard,'' not
+we can say ``GCC is a 100% implementation of the standard'', not
because there is any reason to actually use it.
POSIX.2 specifies that @samp{df} and @samp{du} must output sizes by
POSIX is never a problem in practice, and it is very useful.
In particular, don't reject a new feature, or remove an old one,
-merely because a standard says it is ``forbidden'' or ``deprecated.''
+merely because a standard says it is ``forbidden'' or ``deprecated''.
+
@node Semantics
@section Writing Robust Programs
are silently truncated''. This is not acceptable in a GNU utility.
@cindex @code{NUL} characters
+@findex libiconv
Utilities reading files should not drop NUL characters, or any other
nonprinting characters @emph{including those with codes above 0177}.
The only sensible exceptions would be utilities specifically intended
-for interface to certain types of terminals or printers
-that can't handle those characters.
-Whenever possible, try to make programs work properly with
-sequences of bytes that represent multibyte characters, using encodings
-such as UTF-8 and others.
+for interface to certain types of terminals or printers that can't
+handle those characters. Whenever possible, try to make programs work
+properly with sequences of bytes that represent multibyte characters;
+UTF-8 is the most important.
@cindex error messages
-Check every system call for an error return, unless you know you wish to
-ignore errors. Include the system error text (from @code{perror} or
-equivalent) in @emph{every} error message resulting from a failing
-system call, as well as the name of the file if any and the name of the
-utility. Just ``cannot open foo.c'' or ``stat failed'' is not
-sufficient.
+Check every system call for an error return, unless you know you wish
+to ignore errors. Include the system error text (from @code{perror},
+@code{strerror}, or equivalent) in @emph{every} error message
+resulting from a failing system call, as well as the name of the file
+if any and the name of the utility. Just ``cannot open foo.c'' or
+``stat failed'' is not sufficient.
@cindex @code{malloc} return value
@cindex memory allocation failure
@cindex signal handling
The preferred signal handling facilities are the BSD variant of
-@code{signal}, and the @sc{posix} @code{sigaction} function; the
+@code{signal}, and the POSIX @code{sigaction} function; the
alternative USG @code{signal} interface is an inferior design.
-Nowadays, using the @sc{posix} signal functions may be the easiest way
+Nowadays, using the POSIX signal functions may be the easiest way
to make a program portable. If you use @code{signal}, then on GNU/Linux
systems running GNU libc version 1, you should include
@file{bsd/signal.h} instead of @file{signal.h}, so as to get BSD
avoid this problem by creating temporary files in this manner:
@example
-fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0600);
+fd = open (filename, O_WRONLY | O_CREAT | O_EXCL, 0600);
@end example
@noindent
-or by using the @code{mkstemps} function from libiberty.
+or by using the @code{mkstemps} function from Gnulib
+(@pxref{mkstemps,,, gnulib, Gnulib}).
+
+In bash, use @code{set -C} (long name @code{noclobber}) to avoid this
+problem. In addition, the @code{mktemp} utility is a more general
+solution for creating temporary files from shell scripts
+(@pxref{mktemp invocation,,, coreutils, GNU Coreutils}).
-In bash, use @code{set -C} to avoid this problem.
@node Libraries
@section Library Behavior
Error messages from compilers should look like this:
@example
-@var{source-file-name}:@var{lineno}: @var{message}
+@var{sourcefile}:@var{lineno}: @var{message}
@end example
@noindent
If you want to mention the column number, use one of these formats:
@example
-@var{source-file-name}:@var{lineno}:@var{column}: @var{message}
-@var{source-file-name}:@var{lineno}.@var{column}: @var{message}
+@var{sourcefile}:@var{lineno}:@var{column}: @var{message}
+@var{sourcefile}:@var{lineno}.@var{column}: @var{message}
@end example
@noindent
Line numbers should start from 1 at the beginning of the file, and
-column numbers should start from 1 at the beginning of the line. (Both
-of these conventions are chosen for compatibility.) Calculate column
-numbers assuming that space and all ASCII printing characters have
-equal width, and assuming tab stops every 8 columns.
+column numbers should start from 1 at the beginning of the line.
+(Both of these conventions are chosen for compatibility.) Calculate
+column numbers assuming that space and all ASCII printing characters
+have equal width, and assuming tab stops every 8 columns. For
+non-ASCII characters, Unicode character widths should be used when in
+a UTF-8 locale; GNU libc and GNU gnulib provide suitable
+@code{wcwidth} functions.
The error message can also give both the starting and ending positions
of the erroneous text. There are several formats so that you can
Here are the possible formats:
@example
-@var{source-file-name}:@var{lineno-1}.@var{column-1}-@var{lineno-2}.@var{column-2}: @var{message}
-@var{source-file-name}:@var{lineno-1}.@var{column-1}-@var{column-2}: @var{message}
-@var{source-file-name}:@var{lineno-1}-@var{lineno-2}: @var{message}
+@var{sourcefile}:@var{line1}.@var{column1}-@var{line2}.@var{column2}: @var{message}
+@var{sourcefile}:@var{line1}.@var{column1}-@var{column2}: @var{message}
+@var{sourcefile}:@var{line1}-@var{line2}: @var{message}
@end example
@noindent
When an error is spread over several files, you can use this format:
@example
-@var{file-1}:@var{lineno-1}.@var{column-1}-@var{file-2}:@var{lineno-2}.@var{column-2}: @var{message}
+@var{file1}:@var{line1}.@var{column1}-@var{file2}:@var{line2}.@var{column2}: @var{message}
@end example
Error messages from other noninteractive programs should look like this:
@example
-@var{program}:@var{source-file-name}:@var{lineno}: @var{message}
+@var{program}:@var{sourcefile}:@var{lineno}: @var{message}
@end example
@noindent
If you want to mention the column number, use this format:
@example
-@var{program}:@var{source-file-name}:@var{lineno}:@var{column}: @var{message}
+@var{program}:@var{sourcefile}:@var{lineno}:@var{column}: @var{message}
@end example
In an interactive program (one that is reading commands from a
like @code{ls} except that its default output format is always
multi-column format.
+
@node Graphical Interfaces
@section Standards for Graphical Interfaces
@cindex graphical user interface
+@cindex interface styles
+@cindex user interface styles
-@cindex gtk+
+@cindex GTK+
When you write a program that provides a graphical user interface,
-please make it work with X Windows and the GTK+ toolkit unless the
-functionality specifically requires some alternative (for example,
-``displaying jpeg images while in console mode'').
+please make it work with the X Window System and the GTK+ toolkit
+unless the functionality specifically requires some alternative (for
+example, ``displaying jpeg images while in console mode'').
In addition, please provide a command-line interface to control the
functionality. (In many cases, the graphical user interface can be a
separate program which invokes the command-line program.) This is
so that the same jobs can be done from scripts.
-@cindex corba
-@cindex gnome
-Please also consider providing a CORBA interface (for use from GNOME), a
-library interface (for use from C), and perhaps a keyboard-driven
-console interface (for use by users from console mode). Once you are
-doing the work to provide the functionality and the graphical interface,
-these won't be much extra work.
+@cindex CORBA
+@cindex GNOME
+@cindex D-bus
+@cindex keyboard interface
+@cindex library interface
+Please also consider providing a D-bus interface for use from other
+running programs, such as within GNOME. (GNOME used to use CORBA
+for this, but that is being phased out.) In addition, consider
+providing a library interface (for use from C), and perhaps a
+keyboard-driven console interface (for use by users from console
+mode). Once you are doing the work to provide the functionality and
+the graphical interface, these won't be much extra work.
@node Command-Line Interfaces
@section Standards for Command Line Interfaces
@cindex command-line interface
@findex getopt
-It is a good idea to follow the @sc{posix} guidelines for the
+It is a good idea to follow the POSIX guidelines for the
command-line options of a program. The easiest way to do this is to use
@code{getopt} to parse them. Note that the GNU version of @code{getopt}
will normally permit options anywhere among the arguments unless the
-special argument @samp{--} is used. This is not what @sc{posix}
+special argument @samp{--} is used. This is not what POSIX
specifies; it is a GNU extension.
@cindex long-named options
(preferably @samp{-o} or @samp{--output}). Even if you allow an output
file name as an ordinary argument for compatibility, try to provide an
option as another way to specify it. This will lead to more consistency
-among GNU utilities, and fewer idiosyncracies for users to remember.
+among GNU utilities, and fewer idiosyncrasies for users to remember.
@cindex standard command-line options
@cindex options, standard command-line
output the same information as invoking @samp{p.cgi --help} from the
command line.
-@table @code
-@cindex @samp{--version} option
-@item --version
-This option should direct the program to print information about its name,
-version, origin and legal status, all on standard output, and then exit
-successfully. Other options and arguments should be ignored once this
-is seen, and the program should not perform its normal function.
+@menu
+* --version:: The standard output for --version.
+* --help:: The standard output for --help.
+@end menu
+
+@node --version
+@subsection @option{--version}
+
+@cindex @samp{--version} output
+
+The standard @code{--version} option should direct the program to
+print information about its name, version, origin and legal status,
+all on standard output, and then exit successfully. Other options and
+arguments should be ignored once this is seen, and the program should
+not perform its normal function.
@cindex canonical name of a program
@cindex program's canonical name
program's version number, you can mention the package version number
just before the close-parenthesis.
-If you @strong{need} to mention the version numbers of libraries which
+If you @emph{need} to mention the version numbers of libraries which
are distributed separately from the package which contains this program,
you can do so by printing an additional line of version info for each
library you want to mention. Use the same format for these lines as for
copyright notice. If more than one copyright notice is called for, put
each on a separate line.
-Next should follow a brief statement that the program is free software,
-and that users are free to copy and change it on certain conditions. If
-the program is covered by the GNU GPL, say so here. Also mention that
-there is no warranty, to the extent permitted by law.
+Next should follow a line stating the license, preferably using one of
+abbreviations below, and a brief statement that the program is free
+software, and that users are free to copy and change it. Also mention
+that there is no warranty, to the extent permitted by law. See
+recommended wording below.
It is ok to finish the output with a list of the major authors of the
program, as a way of giving credit.
Here's an example of output that follows these rules:
@smallexample
-GNU Emacs 19.34.5
-Copyright (C) 1996 Free Software Foundation, Inc.
-GNU Emacs comes with NO WARRANTY,
-to the extent permitted by law.
-You may redistribute copies of GNU Emacs
-under the terms of the GNU General Public License.
-For more information about these matters,
-see the files named COPYING.
+GNU hello 2.3
+Copyright (C) 2007 Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
+This is free software: you are free to change and redistribute it.
+There is NO WARRANTY, to the extent permitted by law.
@end smallexample
You should adapt this to your program, of course, filling in the proper
versions' changes. You don't have to mention the name of the program in
these notices, if that is inconvenient, since it appeared in the first
line. (The rules are different for copyright notices in source files;
-see @ref{Copyright Notices,,,maintain,Information for GNU Maintainers}.)
+@pxref{Copyright Notices,,,maintain,Information for GNU Maintainers}.)
Translations of the above lines must preserve the validity of the
copyright notices (@pxref{Internationalization}). If the translation's
the English word ``Copyright''; translations into other languages do not
have legal significance.
+Finally, here is the table of our suggested license abbreviations.
+Any abbreviation can be followed by @samp{v@var{version}[+]}, meaning
+that particular version, or later versions with the @samp{+}, as shown
+above. In the case of a GNU license, @emph{always} indicate the permitted
+versions in this way.
-@cindex @samp{--help} option
-@item --help
-This option should output brief documentation for how to invoke the
-program, on standard output, then exit successfully. Other options and
-arguments should be ignored once this is seen, and the program should
-not perform its normal function.
+In the case of exceptions for extra permissions with the GPL, we use
+@samp{/} for a separator; the version number can follow the license
+abbreviation as usual, as in the examples below.
+
+@table @asis
+@item GPL
+GNU General Public License, @url{http://www.gnu.org/@/licenses/@/gpl.html}.
+
+@item LGPL
+GNU Lesser General Public License, @url{http://www.gnu.org/@/licenses/@/lgpl.html}.
+
+@item GPL/Ada
+GNU GPL with the exception for Ada.
+
+@item Apache
+The Apache Software Foundation license,
+@url{http://www.apache.org/@/licenses}.
+
+@item Artistic
+The Artistic license used for Perl, @url{http://dev.perl.org/licenses/artistic.html}.
+
+@item Expat
+The Expat license, @url{http://www.jclark.com/@/xml/@/copying.txt}.
+
+@item MPL
+The Mozilla Public License, @url{http://www.mozilla.org/@/MPL/}.
+
+@item OBSD
+The original (4-clause) BSD license, incompatible with the GNU GPL
+@url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#6}.
+
+@item PHP
+The license used for PHP, @url{http://www.php.net/@/license/}.
+
+@item public domain
+The non-license that is being in the public domain,
+@url{http://www.gnu.org/@/licenses/@/license-list.html#PublicDomain}.
+
+@item Python
+The license for Python, @url{http://www.python.org/@/2.0.1/@/license.html}.
+
+@item RBSD
+The revised (3-clause) BSD, compatible with the GNU GPL,@*
+@url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#5}.
+
+@item X11
+The simple non-copyleft license used for most versions of the X Window
+System, @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#3}.
+
+@item Zlib
+The license for Zlib, @url{http://www.gzip.org/@/zlib/@/zlib_license.html}.
+
+@end table
+
+More information about these licenses and many more are on the GNU
+licensing web pages,
+@url{http://www.gnu.org/@/licenses/@/license-list.html}.
+
+
+@node --help
+@subsection @option{--help}
+
+@cindex @samp{--help} output
+
+The standard @code{--help} option should output brief documentation
+for how to invoke the program, on standard output, then exit
+successfully. Other options and arguments should be ignored once this
+is seen, and the program should not perform its normal function.
@cindex address for bug reports
@cindex bug reports
-Near the end of the @samp{--help} option's output there should be a line
-that says where to mail bug reports. It should have this format:
+Near the end of the @samp{--help} option's output, please place lines
+giving the email address for bug reports, the package's home page
+(normally @indicateurl{http://www.gnu.org/software/@var{pkg}}, and the
+general page for help using GNU programs. The format should be like this:
@example
-Report bugs to @var{mailing-address}.
+Report bugs to: @var{mailing-address}
+@var{pkg} home page: <http://www.gnu.org/software/@var{pkg}/>
+General help using GNU software: <http://www.gnu.org/gethelp/>
@end example
-@end table
+
+It is ok to mention other appropriate mailing lists and web pages.
+
+
+@node Dynamic Plug-In Interfaces
+@section Standards for Dynamic Plug-in Interfaces
+@cindex plug-ins
+@cindex dynamic plug-ins
+
+Another aspect of keeping free programs free is encouraging
+development of free plug-ins, and discouraging development of
+proprietary plug-ins. Many GNU programs will not have anything like
+plug-ins at all, but those that do should follow these
+practices.
+
+First, the general plug-in architecture design should closely tie the
+plug-in to the original code, such that the plug-in and the base
+program are parts of one extended program. For GCC, for example,
+plug-ins receive and modify GCC's internal data structures, and so
+clearly form an extended program with the base GCC.
+
+@vindex plugin_is_GPL_compatible
+Second, you should require plug-in developers to affirm that their
+plug-ins are released under an appropriate license. This should be
+enforced with a simple programmatic check. For GCC, again for
+example, a plug-in must define the global symbol
+@code{plugin_is_GPL_compatible}, thus asserting that the plug-in is
+released under a GPL-compatible license (@pxref{Plugins,, Plugins,
+gccint, GCC Internals}).
+
+By adding this check to your program you are not creating a new legal
+requirement. The GPL itself requires plug-ins to be free software,
+licensed compatibly. As long as you have followed the first rule above
+to keep plug-ins closely tied to your original program, the GPL and AGPL
+already require those plug-ins to be released under a compatible
+license. The symbol definition in the plug-in---or whatever equivalent
+works best in your program---makes it harder for anyone who might
+distribute proprietary plug-ins to legally defend themselves. If a case
+about this got to court, we can point to that symbol as evidence that
+the plug-in developer understood that the license had this requirement.
+
@node Option Table
@section Table of Long Options
@samp{-v} in @code{gawk}.
@item assume-new
-@samp{-W} in Make.
+@samp{-W} in @code{make}.
@item assume-old
-@samp{-o} in Make.
+@samp{-o} in @code{make}.
@item auto-check
@samp{-a} in @code{recode}.
@samp{-d} in @code{touch}.
@item debug
-@samp{-d} in Make and @code{m4};
+@samp{-d} in @code{make} and @code{m4};
@samp{-t} in Bison.
@item define
@samp{-X} in @code{strip}.
@item dry-run
-@samp{-n} in Make.
+@samp{-n} in @code{make}.
@item ed
@samp{-e} in @code{diff}.
@samp{-N} in @code{diff}.
@item environment-overrides
-@samp{-e} in Make.
+@samp{-e} in @code{make}.
@item eof
@samp{-e} in @code{xargs}.
@samp{-E} in @code{m4}.
@item file
-@samp{-f} in @code{info}, @code{gawk}, Make, @code{mt}, and @code{tar};
-@samp{-n} in @code{sed};
-@samp{-r} in @code{touch}.
+@samp{-f} in @code{gawk}, @code{info}, @code{make}, @code{mt},
+@code{sed}, and @code{tar}.
@item field-separator
@samp{-F} in @code{gawk}.
@samp{-i} in @code{diff} and @code{wdiff}.
@item ignore-errors
-@samp{-i} in Make.
+@samp{-i} in @code{make}.
@item ignore-file
@samp{-i} in @code{ptx}.
@samp{-I} in @code{m4}.
@item include-dir
-@samp{-I} in Make.
+@samp{-I} in @code{make}.
@item incremental
@samp{-G} in @code{tar}.
Used in @code{date}
@item jobs
-@samp{-j} in Make.
+@samp{-j} in @code{make}.
@item just-print
-@samp{-n} in Make.
+@samp{-n} in @code{make}.
@item keep-going
-@samp{-k} in Make.
+@samp{-k} in @code{make}.
@item keep-files
@samp{-k} in @code{csplit}.
@samp{-N} in @code{ls}.
@item load-average
-@samp{-l} in Make.
+@samp{-l} in @code{make}.
@item login
Used in @code{su}.
@samp{-d} in @code{cpio}.
@item makefile
-@samp{-f} in Make.
+@samp{-f} in @code{make}.
@item mapped
Used in GDB.
@samp{-l} in @code{xargs}.
@item max-load
-@samp{-l} in Make.
+@samp{-l} in @code{make}.
@item max-procs
@samp{-P} in @code{xargs}.
@samp{-a} in @code{shar}.
@item new-file
-@samp{-W} in Make.
+@samp{-W} in @code{make}.
@item no-builtin-rules
-@samp{-r} in Make.
+@samp{-r} in @code{make}.
@item no-character-count
@samp{-w} in @code{shar}.
@samp{-2} in @code{wdiff}.
@item no-keep-going
-@samp{-S} in Make.
+@samp{-S} in @code{make}.
@item no-lines
@samp{-l} in Bison.
@samp{-o} in @code{tar}.
@item old-file
-@samp{-o} in Make.
+@samp{-o} in @code{make}.
@item one-file-system
@samp{-l} in @code{tar}, @code{cp}, and @code{du}.
@samp{-L} in @code{cmp}.
@item print-data-base
-@samp{-p} in Make.
+@samp{-p} in @code{make}.
@item print-directory
-@samp{-w} in Make.
+@samp{-w} in @code{make}.
@item print-file-name
@samp{-o} in @code{nm}.
@samp{-X} in @code{shar}.
@item question
-@samp{-q} in Make.
+@samp{-q} in @code{make}.
@item quiet
Used in many programs to inhibit the usual output. Every
Used in GDB.
@item recon
-@samp{-n} in Make.
+@samp{-n} in @code{make}.
@item record-number
@samp{-R} in @code{tar}.
Used in @code{chgrp}, @code{chown}, @code{cp}, @code{ls}, @code{diff},
and @code{rm}.
-@item reference-limit
-Used in @code{makeinfo}.
+@item reference
+@samp{-r} in @code{touch}.
@item references
@samp{-r} in @code{ptx}.
@item socket
Specify a file descriptor for a network server to use for its socket,
instead of opening and binding a new socket. This provides a way to
-run, in a nonpriveledged process, a server that normally needs a
+run, in a non-privileged process, a server that normally needs a
reserved port number.
@item sort
@samp{-S} in @code{shar}.
@item stop
-@samp{-S} in Make.
+@samp{-S} in @code{make}.
@item strict
@samp{-s} in @code{recode}.
@samp{-c} in @code{du}.
@item touch
-@samp{-t} in Make, @code{ranlib}, and @code{recode}.
+@samp{-t} in @code{make}, @code{ranlib}, and @code{recode}.
@item trace
@samp{-t} in @code{m4}.
@samp{-V} in @code{tar}.
@item what-if
-@samp{-W} in Make.
+@samp{-W} in @code{make}.
@item whole-size-limit
@samp{-l} in @code{shar}.
@samp{-z} in @code{gprof}.
@end table
+@node OID Allocations
+@section OID Allocations
+@cindex OID allocations for GNU
+@cindex SNMP
+@cindex LDAP
+@cindex X.509
+
+The OID (object identifier) 1.3.6.1.4.1.11591 has been assigned to the
+GNU Project (thanks to Sergey Poznyakoff). These are used for SNMP,
+LDAP, X.509 certificates, and so on. The web site
+@url{http://www.alvestrand.no/objectid} has a (voluntary) listing of
+many OID assignments.
+
+If you need a new slot for your GNU package, write
+@email{maintainers@@gnu.org}. Here is a list of arcs currently
+assigned:
+
+@example
+@include gnu-oids.texi
+@end example
+
+
@node Memory Usage
@section Memory Usage
@cindex memory usage
If a program typically uses just a few meg of memory, don't bother making any
effort to reduce memory usage. For example, if it is impractical for
other reasons to operate on files more than a few meg long, it is
-reasonable to read entire input files into core to operate on them.
+reasonable to read entire input files into memory to operate on them.
However, for programs such as @code{cat} or @code{tail}, that can
usefully operate on very large files, it is important to avoid using a
If a program works by lines and could be applied to arbitrary
user-supplied input files, it should keep only a line in memory, because
this is not very hard and users will want to be able to operate on input
-files that are bigger than will fit in core all at once.
+files that are bigger than will fit in memory all at once.
If your program creates complicated data structures, just make them in
-core and give a fatal error if @code{malloc} returns zero.
+memory and give a fatal error if @code{malloc} returns zero.
+
+@pindex valgrind
+@cindex memory leak
+Memory analysis tools such as @command{valgrind} can be useful, but
+don't complicate a program merely to avoid their false alarms. For
+example, if memory is used until just before a process exits, don't
+free it simply to silence such a tool.
+
@node File Usage
@section File Usage
when writing GNU software.
@menu
-* Formatting:: Formatting Your Source Code
-* Comments:: Commenting Your Work
-* Syntactic Conventions:: Clean Use of C Constructs
-* Names:: Naming Variables, Functions, and Files
-* System Portability:: Portability between different operating systems
-* CPU Portability:: Supporting the range of CPU types
-* System Functions:: Portability and ``standard'' library functions
-* Internationalization:: Techniques for internationalization
+* Formatting:: Formatting your source code.
+* Comments:: Commenting your work.
+* Syntactic Conventions:: Clean use of C constructs.
+* Names:: Naming variables, functions, and files.
+* System Portability:: Portability among different operating systems.
+* CPU Portability:: Supporting the range of CPU types.
+* System Functions:: Portability and ``standard'' library functions.
+* Internationalization:: Techniques for internationalization.
* Character Set:: Use ASCII by default.
-* Quote Characters:: Use `...' in the C locale.
+* Quote Characters:: Use "..." or '...' in the C locale.
* Mmap:: How you can safely use @code{mmap}.
@end menu
@section Formatting Your Source Code
@cindex formatting source code
+@cindex line length
+@cindex length of source lines
+Please keep the length of source lines to 79 characters or less, for
+maximum readability in the widest range of environments.
+
@cindex open brace
@cindex braces, in C source
+@cindex function definitions, formatting
It is important to put the open-brace that starts the body of a C
-function in column one, and avoid putting any other open-brace or
-open-parenthesis or open-bracket in column one. Several tools look
-for open-braces in column one to find the beginnings of C functions.
-These tools will not work on code not formatted that way.
+function in column one, so that they will start a defun. Several
+tools look for open-braces in column one to find the beginnings of C
+functions. These tools will not work on code not formatted that way.
+
+Avoid putting open-brace, open-parenthesis or open-bracket in column
+one when they are inside a function, so that they won't start a defun.
+The open-brace that starts a @code{struct} body can go in column one
+if you find it useful to treat that definition as a defun.
It is also important for function definitions to start the name of the
function in column one. This helps people to search for function
@dots{}
@end example
+@cindex @code{struct} types, formatting
+@cindex @code{enum} types, formatting
+For @code{struct} and @code{enum} types, likewise put the braces in
+column one, unless the whole contents fits on one line:
+
+@example
+struct foo
+@{
+ int a, b;
+@}
+@exdent @r{or}
+struct foo @{ int a, b; @}
+@end example
+
The rest of this section gives our recommendations for other aspects of
C formatting style, which is also the default style of the @code{indent}
program in version 1.2 and newer. It corresponds to the options
number NODE_NUM'' rather than ``an inode''.
There is usually no purpose in restating the name of the function in
-the comment before it, because the reader can see that for himself.
+the comment before it, because readers can see that for themselves.
There might be an exception when the comment is so long that the function
itself would be off the bottom of the screen.
If you want to do this, then do. The compiler should be your servant,
not your master.
+@pindex clang
+@pindex lint
+Don't make the program ugly just to placate static analysis tools such
+as @command{lint}, @command{clang}, and GCC with extra warnings
+options such as @option{-Wconversion} and @option{-Wundef}. These
+tools can help find bugs and unclear code, but they can also generate
+so many false alarms that it hurts readability to silence them with
+unnecessary casts, wrappers, and other complications. For example,
+please don't insert casts to @code{void} or calls to do-nothing
+functions merely to pacify a lint checker.
+
Declarations of external functions and functions to appear later in the
source file should all go in one place near the beginning of the file
(somewhere before the first function definition in the file), or else
all its uses. This makes the program even cleaner.
Don't use local variables or parameters that shadow global identifiers.
+GCC's @samp{-Wshadow} option can detect this problem.
@cindex multiple variables in a line
Don't declare multiple variables in one declaration that spans lines.
same declaration. Instead, declare the structure tag separately
and then use it to declare the variables or typedefs.
-Try to avoid assignments inside @code{if}-conditions. For example,
-don't write this:
+Try to avoid assignments inside @code{if}-conditions (assignments
+inside @code{while}-conditions are ok). For example, don't write
+this:
@example
if ((foo = (char *) malloc (sizeof *foo)) == 0)
fatal ("virtual memory exhausted");
@end example
-@pindex lint
-Don't make the program ugly to placate @code{lint}. Please don't insert any
-casts to @code{void}. Zero without a cast is perfectly fine as a null
-pointer constant, except when calling a varargs function.
+This example uses zero without a cast as a null pointer constant.
+This is perfectly fine, except that a cast is needed when calling a
+varargs function or when using @code{sizeof}.
@node Names
@section Naming Variables, Functions, and Files
programs. @code{doschk} also reports file names longer than 14
characters.
+
@node System Portability
@section Portability between System Types
@cindex portability, between system types
not paramount.
The primary purpose of GNU software is to run on top of the GNU kernel,
-compiled with the GNU C compiler, on various types of @sc{cpu}. So the
+compiled with the GNU C compiler, on various types of CPU. So the
kinds of portability that are absolutely necessary are quite limited.
But it is important to support Linux-based GNU systems, since they
are the form of GNU that is popular.
Avoid using the format of semi-internal data bases (e.g., directories)
when there is a higher-level alternative (@code{readdir}).
-@cindex non-@sc{posix} systems, and portability
+@cindex non-POSIX systems, and portability
As for systems that are not like Unix, such as MSDOS, Windows, VMS, MVS,
and older Macintosh systems, supporting them is often a lot of work.
When that is the case, it is better to spend your time adding features
hacker terminology, calling something a ``win'' is a form of praise.
You're free to praise Microsoft Windows on your own if you want, but
please don't do this in GNU packages. Instead of abbreviating
-``Windows'' to ``un'', you can write it in full or abbreviate it to
+``Windows'' to ``win'', you can write it in full or abbreviate it to
``woe'' or ``w''. In GNU Emacs, for instance, we use @samp{w32} in
file names of Windows-specific files, but the macro for Windows
conditionals is called @code{WINDOWSNT}.
to move your code into other GNU programs.
@node CPU Portability
-@section Portability between @sc{cpu}s
+@section Portability between CPUs
@cindex data types, and portability
@cindex portability, and data types
-Even GNU systems will differ because of differences among @sc{cpu}
+Even GNU systems will differ because of differences among CPU
types---for example, difference in byte ordering and alignment
requirements. It is absolutely essential to handle these differences.
However, don't make any effort to cater to the possibility that an
@end example
1989 Standard C requires this to work, and we know of only one
-counterexample: 64-bit programs on Microsoft Windows. We will
-leave it to those who want to port GNU programs to that environment
-to figure out how to do it.
+counterexample: 64-bit programs on Microsoft Windows. We will leave
+it to those who want to port GNU programs to that environment to
+figure out how to do it.
Predefined file-size types like @code{off_t} are an exception: they are
longer than @code{long} on many platforms, so code like the above won't
@example
int c;
@dots{}
-while ((c = getchar()) != EOF)
- write(file_descriptor, &c, 1);
-@end example
-
-It used to be ok to not worry about the difference between pointers
-and integers when passing arguments to functions. However, on most
-modern 64-bit machines pointers are wider than @code{int}.
-Conversely, integer types like @code{long long int} and @code{off_t}
-are wider than pointers on most modern 32-bit machines. Hence it's
-often better nowadays to use prototypes to define functions whose
-argument types are not trivial.
-
-In particular, if functions accept varying argument counts or types
-they should be declared using prototypes containing @samp{...} and
-defined using @file{stdarg.h}. For an example of this, please see the
-@uref{http://www.gnu.org/software/gnulib/, Gnulib} error module, which
-declares and defines the following function:
-
-@example
-/* Print a message with `fprintf (stderr, FORMAT, ...)';
- if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM).
- If STATUS is nonzero, terminate the program with `exit (STATUS)'. */
-
-void error (int status, int errnum, const char *format, ...);
+while ((c = getchar ()) != EOF)
+ write (file_descriptor, &c, 1);
@end example
-A simple way to use the Gnulib error module is to obtain the two
-source files @file{error.c} and @file{error.h} from the Gnulib library
-source code repository at
-@uref{http://savannah.gnu.org/cgi-bin/viewcvs/gnulib/gnulib/lib/}.
-Here's a sample use:
+@noindent Instead, use @code{unsigned char} as follows. (The @code{unsigned}
+is for portability to unusual systems where @code{char} is signed and
+where there is integer overflow checking.)
@example
-#include "error.h"
-#include <errno.h>
-#include <stdio.h>
-
-char *program_name = "myprogram";
-
-FILE *
-xfopen (char const *name)
-@{
- FILE *fp = fopen (name, "r");
- if (! fp)
- error (1, errno, "cannot read %s", name);
- return fp;
-@}
+int c;
+while ((c = getchar ()) != EOF)
+ @{
+ unsigned char u = c;
+ write (file_descriptor, &u, 1);
+ @}
@end example
@cindex casting pointers to integers
normal range of addresses you can get from @code{malloc} starts far away
from zero.
+
@node System Functions
@section Calling System Functions
+
+@cindex C library functions, and portability
+@cindex POSIX functions, and portability
@cindex library functions, and portability
@cindex portability, and library functions
-C implementations differ substantially. Standard C reduces but does
-not eliminate the incompatibilities; meanwhile, many GNU packages still
-support pre-standard compilers because this is not hard to do. This
-chapter gives recommendations for how to use the more-or-less standard C
-library functions to avoid unnecessary loss of portability.
-
-@itemize @bullet
-@item
-Don't use the return value of @code{sprintf}. It returns the number of
-characters written on some systems, but not on all systems.
-
-@item
-Be aware that @code{vfprintf} is not always available.
-
-@item
-@code{main} should be declared to return type @code{int}. It should
-terminate either by calling @code{exit} or by returning the integer
-status code; make sure it cannot ever return an undefined value.
-
-@cindex declaration for system functions
-@item
-Don't declare system functions explicitly.
-
-Almost any declaration for a system function is wrong on some system.
-To minimize conflicts, leave it to the system header files to declare
-system functions. If the headers don't declare a function, let it
-remain undeclared.
-
-While it may seem unclean to use a function without declaring it, in
-practice this works fine for most system library functions on the
-systems where this really happens; thus, the disadvantage is only
-theoretical. By contrast, actual declarations have frequently caused
-actual conflicts.
-
-@item
-If you must declare a system function, don't specify the argument types.
-Use an old-style declaration, not a Standard C prototype. The more you
-specify about the function, the more likely a conflict.
-
-@item
-In particular, don't unconditionally declare @code{malloc} or
-@code{realloc}.
-
-Most GNU programs use those functions just once, in functions
-conventionally named @code{xmalloc} and @code{xrealloc}. These
-functions call @code{malloc} and @code{realloc}, respectively, and
-check the results.
-
-Because @code{xmalloc} and @code{xrealloc} are defined in your program,
-you can declare them in other files without any risk of type conflict.
-
-On most systems, @code{int} is the same length as a pointer; thus, the
-calls to @code{malloc} and @code{realloc} work fine. For the few
-exceptional systems (mostly 64-bit machines), you can use
-@strong{conditionalized} declarations of @code{malloc} and
-@code{realloc}---or put these declarations in configuration files
-specific to those systems.
-
-@cindex string library functions
-@item
-The string functions require special treatment. Some Unix systems have
-a header file @file{string.h}; others have @file{strings.h}. Neither
-file name is portable. There are two things you can do: use Autoconf to
-figure out which file to include, or don't include either file.
-
-@item
-If you don't include either strings file, you can't get declarations for
-the string functions from the header file in the usual way.
-
-That causes less of a problem than you might think. The newer standard
-string functions should be avoided anyway because many systems still
-don't support them. The string functions you can use are these:
-
-@example
-strcpy strncpy strcat strncat
-strlen strcmp strncmp
-strchr strrchr
-@end example
-
-The copy and concatenate functions work fine without a declaration as
-long as you don't use their values. Using their values without a
-declaration fails on systems where the width of a pointer differs from
-the width of @code{int}, and perhaps in other cases. It is trivial to
-avoid using their values, so do that.
-
-The compare functions and @code{strlen} work fine without a declaration
-on most systems, possibly all the ones that GNU software runs on.
-You may find it necessary to declare them @strong{conditionally} on a
-few systems.
-
-The search functions must be declared to return @code{char *}. Luckily,
-there is no variation in the data type they return. But there is
-variation in their names. Some systems give these functions the names
-@code{index} and @code{rindex}; other systems use the names
-@code{strchr} and @code{strrchr}. Some systems support both pairs of
-names, but neither pair works on all systems.
-
-You should pick a single pair of names and use it throughout your
-program. (Nowadays, it is better to choose @code{strchr} and
-@code{strrchr} for new programs, since those are the standard
-names.) Declare both of those names as functions returning @code{char
-*}. On systems which don't support those names, define them as macros
-in terms of the other pair. For example, here is what to put at the
-beginning of your file (or in a header) if you want to use the names
-@code{strchr} and @code{strrchr} throughout:
-
-@example
-#ifndef HAVE_STRCHR
-#define strchr index
-#endif
-#ifndef HAVE_STRRCHR
-#define strrchr rindex
-#endif
+Historically, C implementations differed substantially, and many
+systems lacked a full implementation of ANSI/ISO C89. Nowadays,
+however, all practical systems have a C89 compiler and GNU C supports
+almost all of C99 and some of C11. Similarly, most systems implement
+POSIX.1-2001 libraries and tools, and many have POSIX.1-2008.
-char *strchr ();
-char *strrchr ();
-@end example
-@end itemize
+Hence, there is little reason to support old C or non-POSIX systems,
+and you may want to take advantage of standard C and POSIX to write
+clearer, more portable, or faster code. You should use standard
+interfaces where possible; but if GNU extensions make your program
+more maintainable, powerful, or otherwise better, don't hesitate to
+use them. In any case, don't make your own declaration of system
+functions; that's a recipe for conflict.
+
+Despite the standards, nearly every library function has some sort of
+portability issue on some system or another. Here are some examples:
+
+@table @code
+@item open
+Names with trailing @code{/}'s are mishandled on many platforms.
+
+@item printf
+@code{long double} may be unimplemented; floating values Infinity and
+NaN are often mishandled; output for large precisions may be
+incorrect.
+
+@item readlink
+May return @code{int} instead of @code{ssize_t}.
+
+@item scanf
+On Windows, @code{errno} is not set on failure.
+@end table
+
+@cindex Gnulib
+@uref{http://www.gnu.org/software/gnulib/, Gnulib} is a big help in
+this regard. Gnulib provides implementations of standard interfaces
+on many of the systems that lack them, including portable
+implementations of enhanced GNU interfaces, thereby making their use
+portable, and of POSIX-1.2008 interfaces, some of which are missing
+even on up-to-date GNU systems.
+
+@findex xmalloc, in Gnulib
+@findex error messages, in Gnulib
+@findex data structures, in Gnulib
+Gnulib also provides many useful non-standard interfaces; for example,
+C implementations of standard data structures (hash tables, binary
+trees), error-checking type-safe wrappers for memory allocation
+functions (@code{xmalloc}, @code{xrealloc}), and output of error
+messages.
+
+Gnulib integrates with GNU Autoconf and Automake to remove much of the
+burden of writing portable code from the programmer: Gnulib makes your
+configure script automatically determine what features are missing and
+use the Gnulib code to supply the missing pieces.
+
+The Gnulib and Autoconf manuals have extensive sections on
+portability: @ref{Top,, Introduction, gnulib, Gnulib} and
+@pxref{Portable C and C++,,, autoconf, Autoconf}. Please consult them
+for many more details.
-Here we assume that @code{HAVE_STRCHR} and @code{HAVE_STRRCHR} are
-macros defined in systems where the corresponding functions exist.
-One way to get them properly defined is to use Autoconf.
@node Internationalization
@section Internationalization
around each string that might need translation---like this:
@example
-printf (gettext ("Processing file `%s'..."));
+printf (gettext ("Processing file '%s'..."), file);
@end example
@noindent
This permits GNU gettext to replace the string @code{"Processing file
-`%s'..."} with a translated version.
+'%s'..."} with a translated version.
Once a program uses gettext, please make a point of writing calls to
@code{gettext} when you add new strings that call for translation.
Here is an example of what not to do:
-@example
+@smallexample
printf ("%s is full", capacity > 5000000 ? "disk" : "floppy disk");
-@end example
+@end smallexample
If you apply gettext to all strings, like this,
-@example
+@smallexample
printf (gettext ("%s is full"),
capacity > 5000000 ? gettext ("disk") : gettext ("floppy disk"));
-@end example
+@end smallexample
@noindent
the translator will hardly know that "disk" and "floppy disk" are meant to
Adding @code{gettext} calls to this code cannot give correct results for
all languages, because negation in some languages requires adding words
at more than one place in the sentence. By contrast, adding
-@code{gettext} calls does the job straightfowardly if the code starts
+@code{gettext} calls does the job straightforwardly if the code starts
out like this:
@example
the application domain. For example, if source code deals with the
French Revolutionary calendar, it is OK if its literal strings contain
accented characters in month names like ``Flor@'eal''. Also, it is OK
-to use non-ASCII characters to represent proper names of contributors in
-change logs (@pxref{Change Logs}).
+(but not required) to use non-ASCII characters to represent proper
+names of contributors in change logs (@pxref{Change Logs}).
-If you need to use non-ASCII characters, you should normally stick with
-one encoding, as one cannot in general mix encodings reliably.
+If you need to use non-ASCII characters, you should normally stick
+with one encoding, certainly within a single file. UTF-8 is likely to
+be the best choice.
@node Quote Characters
@cindex quote characters
@cindex locale-specific quote characters
@cindex left quote
+@cindex right quote
+@cindex opening quote
+@cindex single quote
+@cindex double quote
@cindex grave accent
+@set txicodequoteundirected
+@set txicodequotebacktick
-In the C locale, GNU programs should stick to plain ASCII for quotation
-characters in messages to users: preferably 0x60 (@samp{`}) for left
-quotes and 0x27 (@samp{'}) for right quotes. It is ok, but not
-required, to use locale-specific quotes in other locales.
+In the C locale, the output of GNU programs should stick to plain
+ASCII for quotation characters in messages to users: preferably 0x22
+(@samp{"}) or 0x27 (@samp{'}) for both opening and closing quotes.
+Although GNU programs traditionally used 0x60 (@samp{`}) for opening
+and 0x27 (@samp{'}) for closing quotes, nowadays quotes @samp{`like
+this'} are typically rendered asymmetrically, so quoting @samp{"like
+this"} or @samp{'like this'} typically looks better.
-The @uref{http://www.gnu.org/software/gnulib/, Gnulib} @code{quote} and
-@code{quotearg} modules provide a reasonably straightforward way to
-support locale-specific quote characters, as well as taking care of
-other issues, such as quoting a filename that itself contains a quote
-character. See the Gnulib documentation for usage details.
+It is ok, but not required, for GNU programs to generate
+locale-specific quotes in non-C locales. For example:
+
+@example
+printf (gettext ("Processing file '%s'..."), file);
+@end example
-In any case, the documentation for your program should clearly specify
-how it does quoting, if different than the preferred method of @samp{`}
-and @samp{'}. This is especially important if the output of your
-program is ever likely to be parsed by another program.
+@noindent
+Here, a French translation might cause @code{gettext} to return the
+string @code{"Traitement de fichier
+@guilsinglleft{}@tie{}%s@tie{}@guilsinglright{}..."}, yielding quotes
+more appropriate for a French locale.
-Quotation characters are a difficult area in the computing world at
-this time: there are no true left or right quote characters in Latin1;
-the @samp{`} character we use was standardized there as a grave
-accent. Moreover, Latin1 is still not universally usable.
+Sometimes a program may need to use opening and closing quotes
+directly. By convention, @code{gettext} translates the string
+@samp{"`"} to the opening quote and the string @samp{"'"} to the
+closing quote, and a program can use these translations. Generally,
+though, it is better to translate quote characters in the context of
+longer strings.
-Unicode contains the unambiguous quote characters required, and its
-common encoding UTF-8 is upward compatible with Latin1. However,
-Unicode and UTF-8 are not universally well-supported, either.
+If the output of your program is ever likely to be parsed by another
+program, it is good to provide an option that makes this parsing
+reliable. For example, you could escape special characters using
+conventions from the C language or the Bourne shell. See for example
+the option @option{--quoting-style} of GNU @code{ls}.
-This may change over the next few years, and then we will revisit
-this.
+@clear txicodequoteundirected
+@clear txicodequotebacktick
@node Mmap
@section Mmap
@findex mmap
-Don't assume that @code{mmap} either works on all files or fails
-for all files. It may work on some files and fail on others.
+If you use @code{mmap} to read or write files, don't assume it either
+works on all files or fails for all files. It may work on some files
+and fail on others.
The proper way to use @code{mmap} is to try it on the specific file for
which you want to use it---and if @code{mmap} doesn't work, fall back on
The reason this precaution is needed is that the GNU kernel (the HURD)
provides a user-extensible file system, in which there can be many
-different kinds of ``ordinary files.'' Many of them support
+different kinds of ``ordinary files''. Many of them support
@code{mmap}, but some do not. It is important to make programs handle
all these kinds of files.
+
@node Documentation
@chapter Documenting Programs
@cindex documentation
* Manual Credits:: Giving credit to documentation contributors.
* Printed Manuals:: Mentioning the printed manual.
* NEWS File:: NEWS files supplement manuals.
-* Change Logs:: Recording Changes
+* Change Logs:: Recording changes.
* Man Pages:: Man pages are secondary.
* Reading other Manuals:: How far you can go in learning
from other manuals.
the framework for a beginner to understand the rest of the manual. The
Bison manual provides a good example of how to do this.
-To serve as a reference, a manual should have an Index that list all the
-functions, variables, options, and important concepts that are part of
-the program. One combined Index should do for a short manual, but
-sometimes for a complex package it is better to use multiple indices.
-The Texinfo manual includes advice on preparing good index entries, see
-@ref{Index Entries, , Making Index Entries, texinfo, GNU Texinfo}, and
-see @ref{Indexing Commands, , Defining the Entries of an
+To serve as a reference, a manual should have an Index that lists all
+the functions, variables, options, and important concepts that are
+part of the program. One combined Index should do for a short manual,
+but sometimes for a complex package it is better to use multiple
+indices. The Texinfo manual includes advice on preparing good index
+entries, see @ref{Index Entries, , Making Index Entries, texinfo, GNU
+Texinfo}, and see @ref{Indexing Commands, , Defining the Entries of an
Index, texinfo, GNU Texinfo}.
Don't use Unix man pages as a model for how to write GNU documentation;
variables. The previous descriptions of functions and variables in the
section will also have given information about the topic. A description
written to stand alone would repeat some of that information; this
-redundance looks bad. Meanwhile, the informality that is acceptable in
+redundancy looks bad. Meanwhile, the informality that is acceptable in
a documentation string is totally unacceptable in a manual.
The only good way to use documentation strings in writing a good manual
@node Change Log Concepts
@subsection Change Log Concepts
+@cindex change set
+@cindex batch of changes
You can think of the change log as a conceptual ``undo list'' which
explains how earlier versions were different from the current version.
-People can see the current version; they don't need the change log
-to tell them what is in it. What they want from a change log is a
-clear explanation of how the earlier version differed.
+People can see the current version; they don't need the change log to
+tell them what is in it. What they want from a change log is a clear
+explanation of how the earlier version differed. Each @dfn{entry} in
+a change log describes either an individual change or the smallest
+batch of changes that belong together, also known as a @dfn{change
+set}.
+@cindex title, change log entry
+@cindex description, change log entry
+For later reference or for summarizing, sometimes it is useful to
+start the entry with a one-line description (sometimes called a
+@dfn{title}) to describe its overall purpose.
+
+In the past, we recommended not mentioning changes in non-software
+files (manuals, help files, media files, etc.)@: in change logs.
+However, we've been advised that it is a good idea to include them,
+for the sake of copyright records.
The change log file is normally called @file{ChangeLog} and covers an
entire directory. Each directory can have its own change log, or a
-directory can use the change log of its parent directory--it's up to
+directory can use the change log of its parent directory---it's up to
you.
Another alternative is to record change log information with a version
to a @file{ChangeLog} file using @code{rcs2log}; in Emacs, the command
@kbd{C-x v a} (@code{vc-update-change-log}) does the job.
-There's no need to describe the full purpose of the changes or how they
-work together. If you think that a change calls for explanation, you're
-probably right. Please do explain it---but please put the explanation
-in comments in the code, where people will see it whenever they see the
-code. For example, ``New function'' is enough for the change log when
-you add a function, because there should be a comment before the
-function definition to explain what it does.
+For changes to code, there's no need to describe the full purpose of
+the changes or how they work together. If you think that a change
+calls for explanation, you're probably right. Please do explain
+it---but please put the full explanation in comments in the code,
+where people will see it whenever they see the code. For example,
+``New function'' is enough for the change log when you add a function,
+because there should be a comment before the function definition to
+explain what it does.
-In the past, we recommended not mentioning changes in non-software
-files (manuals, help files, etc.) in change logs. However, we've been
-advised that it is a good idea to include them, for the sake of
-copyright records.
-
-However, sometimes it is useful to write one line to describe the
-overall purpose of a batch of changes.
+For changes to files that do not support a comment syntax (e.g., media
+files), it is ok to include the full explanation in the change log file,
+after the title and before the list of individual changes.
The easiest way to add an entry to @file{ChangeLog} is with the Emacs
-command @kbd{M-x add-change-log-entry}. An entry should have an
-asterisk, the name of the changed file, and then in parentheses the name
-of the changed functions, variables or whatever, followed by a colon.
-Then describe the changes you made to that function or variable.
+command @kbd{M-x add-change-log-entry}. An individual change should
+have an asterisk, the name of the changed file, and then in
+parentheses the name of the changed functions, variables or whatever,
+followed by a colon. Then describe the changes you made to that
+function or variable.
+
@node Style of Change Logs
@subsection Style of Change Logs
this is not a good idea, since searching for @code{jump-to-register} or
@code{insert-register} would not find that entry.
-Separate unrelated change log entries with blank lines. When two
-entries represent parts of the same change, so that they work together,
-then don't put blank lines between them. Then you can omit the file
-name and the asterisk when successive entries are in the same file.
+Separate unrelated change log entries with blank lines. Don't put
+blank lines between individual changes of an entry. You can omit the
+file name and the asterisk when successive individual changes are in
+the same file.
Break long lists of function names by closing continued lines with
@samp{)}, rather than @samp{,}, and opening the continuation with
@example
* keyboard.c (menu_bar_items, tool_bar_items)
-(Fexecute_extended_command): Deal with `keymap' property.
+(Fexecute_extended_command): Deal with 'keymap' property.
@end example
When you install someone else's changes, put the contributor's name in
@cindex conditional changes, and change logs
@cindex change logs, conditional changes
-C programs often contain compile-time @code{#if} conditionals. Many
-changes are conditional; sometimes you add a new definition which is
-entirely contained in a conditional. It is very useful to indicate in
-the change log the conditions for which the change applies.
+Source files can often contain code that is conditional to build-time
+or static conditions. For example, C programs can contain
+compile-time @code{#if} conditionals; programs implemented in
+interpreted languages can contain module imports of function
+definitions that are only performed for certain versions of the
+interpreter; and Automake @file{Makefile.am} files can contain
+variable definitions or target declarations that are only to be
+considered if a configure-time Automake conditional is true.
-Our convention for indicating conditional changes is to use square
-brackets around the name of the condition.
+Many changes are conditional as well: sometimes you add a new variable,
+or function, or even a new program or library, which is entirely
+dependent on a build-time condition. It is useful to indicate
+in the change log the conditions for which a change applies.
-Here is a simple example, describing a change which is conditional but
-does not have a function or entity name associated with it:
+Our convention for indicating conditional changes is to use
+@emph{square brackets around the name of the condition}.
+
+Conditional changes can happen in numerous scenarios and with many
+variations, so here are some examples to help clarify. This first
+example describes changes in C, Perl, and Python files which are
+conditional but do not have an associated function or entity name:
@example
-* xterm.c [SOLARIS2]: Include string.h.
+* xterm.c [SOLARIS2]: Include <string.h>.
+* FilePath.pm [$^O eq 'VMS']: Import the VMS::Feature module.
+* framework.py [sys.version_info < (2, 6)]: Make "with" statement
+ available by importing it from __future__,
+ to support also python 2.5.
@end example
-Here is an entry describing a new definition which is entirely
-conditional. This new definition for the macro @code{FRAME_WINDOW_P} is
-used only when @code{HAVE_X_WINDOWS} is defined:
+Our other examples will for simplicity be limited to C, as the minor
+changes necessary to adapt them to other languages should be
+self-evident.
+
+Next, here is an entry describing a new definition which is entirely
+conditional: the C macro @code{FRAME_WINDOW_P} is defined (and used)
+only when the macro @code{HAVE_X_WINDOWS} is defined:
@example
* frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined.
@end example
-Here is an entry for a change within the function @code{init_display},
-whose definition as a whole is unconditional, but the changes themselves
-are contained in a @samp{#ifdef HAVE_LIBNCURSES} conditional:
+Next, an entry for a change within the function @code{init_display},
+whose definition as a whole is unconditional, but the changes
+themselves are contained in a @samp{#ifdef HAVE_LIBNCURSES}
+conditional:
@example
* dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent.
@end example
-Here is an entry for a change that takes affect only when
+Finally, here is an entry for a change that takes effect only when
a certain macro is @emph{not} defined:
@example
-(gethostname) [!HAVE_SOCKETS]: Replace with winsock version.
+* host.c (gethostname) [!HAVE_SOCKETS]: Replace with winsock version.
@end example
+
@node Indicating the Part Changed
@subsection Indicating the Part Changed
is more authoritative. The note should say how to access the Texinfo
documentation.
-Be sure that man pages include a copyright statement and free
-license. The simple all-permissive license is appropriate for simple
-man pages:
-
-@example
-Copying and distribution of this file, with or without modification,
-are permitted in any medium without royalty provided the copyright
-notice and this notice are preserved.
-@end example
+Be sure that man pages include a copyright statement and free license.
+The simple all-permissive license is appropriate for simple man pages
+(@pxref{License Notices for Other Files,,,maintain,Information for GNU
+Maintainers}).
For long man pages, with enough explanation and documentation that
they can be considered true manuals, use the GFDL (@pxref{License for
all GNU software.
@menu
-* Configuration:: How Configuration Should Work
-* Makefile Conventions:: Makefile Conventions
-* Releases:: Making Releases
+* Configuration:: How configuration of GNU packages should work.
+* Makefile Conventions:: Makefile conventions.
+* Releases:: Making releases
@end menu
@node Configuration
Each GNU distribution should come with a shell script named
@code{configure}. This script is given arguments which describe the
kind of machine and system you want to compile the program for.
-
The @code{configure} script must record the configuration options so
that they affect compilation.
-One way to do this is to make a link from a standard name such as
-@file{config.h} to the proper configuration file for the chosen system.
-If you use this technique, the distribution should @emph{not} contain a
-file named @file{config.h}. This is so that people won't be able to
-build the program without configuring it first.
+The description here is the specification of the interface for the
+@code{configure} script in GNU packages. Many packages implement it
+using GNU Autoconf (@pxref{Top,, Introduction, autoconf, Autoconf})
+and/or GNU Automake (@pxref{Top,, Introduction, automake, Automake}),
+but you do not have to use these tools. You can implement it any way
+you like; for instance, by making @code{configure} be a wrapper around
+a completely different configuration system.
+
+Another way for the @code{configure} script to operate is to make a
+link from a standard name such as @file{config.h} to the proper
+configuration file for the chosen system. If you use this technique,
+the distribution should @emph{not} contain a file named
+@file{config.h}. This is so that people won't be able to build the
+program without configuring it first.
Another thing that @code{configure} can do is to edit the Makefile. If
you do this, the distribution should @emph{not} contain a file named
possible, @code{configure} can add to the Makefile a variable named
@code{srcdir} whose value is precisely the specified directory.
+In addition, the @samp{configure} script should take options
+corresponding to most of the standard directory variables
+(@pxref{Directory Variables}). Here is the list:
+
+@example
+--prefix --exec-prefix --bindir --sbindir --libexecdir --sysconfdir
+--sharedstatedir --localstatedir --runstatedir
+--libdir --includedir --oldincludedir
+--datarootdir --datadir --infodir --localedir --mandir --docdir
+--htmldir --dvidir --pdfdir --psdir
+@end example
+
The @code{configure} script should also take an argument which specifies the
type of system to build the program for. This argument should look like
this:
alternatives for how to describe a machine. Thus,
@samp{athlon-pc-gnu/linux} would be a valid alias. There is a shell
script called
-@uref{http://savannah.gnu.org/@/cgi-bin/@/viewcvs/@/*checkout*/@/config/@/config/@/config.sub,
+@uref{http://git.savannah.gnu.org/@/gitweb/@/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD,
@file{config.sub}} that you can use as a subroutine to validate system
types and canonicalize aliases.
i686-pc-linux-gnu}. When the build type is not specified by an option
or argument, the @code{configure} script should normally guess it using
the shell script
-@uref{http://savannah.gnu.org/@/cgi-bin/@/viewcvs/@/*checkout*/@/config/@/config/@/config.guess,
+@uref{http://git.savannah.gnu.org/@/gitweb/@/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD,
@file{config.guess}}.
@cindex optional features, configure-time
Other options are permitted to specify in more detail the software
-or hardware present on the machine, and include or exclude optional
-parts of the package:
+or hardware present on the machine, to include or exclude optional parts
+of the package, or to adjust the name of some tools or arguments to them:
@table @samp
@item --enable-@var{feature}@r{[}=@var{parameter}@r{]}
Do not use a @samp{--with} option to specify the file name to use to
find certain files. That is outside the scope of what @samp{--with}
options are for.
+
+@item @var{variable}=@var{value}
+Set the value of the variable @var{variable} to @var{value}. This is
+used to override the default values of commands or arguments in the
+build process. For example, the user could issue @samp{configure
+CFLAGS=-g CXXFLAGS=-g} to build with debugging information and without
+the default optimization.
+
+Specifying variables as arguments to @code{configure}, like this:
+@example
+./configure CC=gcc
+@end example
+is preferable to setting them in environment variables:
+@example
+CC=gcc ./configure
+@end example
+as it helps to recreate the same configuration later with
+@file{config.status}. However, both methods should be supported.
@end table
-All @code{configure} scripts should accept all of these ``detail''
-options, whether or not they make any difference to the particular
-package at hand. In particular, they should accept any option that
-starts with @samp{--with-} or @samp{--enable-}. This is so users will
-be able to configure an entire GNU source tree at once with a single set
-of options.
+All @code{configure} scripts should accept all of the ``detail''
+options and the variable settings, whether or not they make any
+difference to the particular package at hand. In particular, they
+should accept any option that starts with @samp{--with-} or
+@samp{--enable-}. This is so users will be able to configure an
+entire GNU source tree at once with a single set of options.
You will note that the categories @samp{--with-} and @samp{--enable-}
are narrow: they @strong{do not} provide a place for any sort of option
@section Making Releases
@cindex packaging
+@cindex version numbers, for releases
You should identify each release with a pair of version numbers, a
major version and a minor. We have no objection to using more than
two numbers, but it is very unlikely that you really need them.
source files by programs under the control of the Makefile.
@cindex @file{README} file
-The distribution should contain a file named @file{README} which gives
-the name of the package, and a general description of what it does. It
-is also good to explain the purpose of each of the first-level
-subdirectories in the package, if there are any. The @file{README} file
-should either state the version number of the package, or refer to where
-in the package it can be found.
-
-The @file{README} file should refer to the file @file{INSTALL}, which
-should contain an explanation of the installation procedure.
-
-The @file{README} file should also refer to the file which contains the
-copying conditions. The GNU GPL, if used, should be in a file called
-@file{COPYING}. If the GNU LGPL is used, it should be in a file called
-@file{COPYING.LIB}.
-
-Naturally, all the source files must be in the distribution. It is okay
-to include non-source files in the distribution, provided they are
-up-to-date and machine-independent, so that building the distribution
-normally will never modify them. We commonly include non-source files
-produced by Bison, @code{lex}, @TeX{}, and @code{makeinfo}; this helps avoid
+The distribution should contain a file named @file{README} with a
+general overview of the package:
+
+@itemize
+@item the name of the package;
+
+@item the version number of the package, or refer to where in the
+package the version can be found;
+
+@item a general description of what the package does;
+
+@item a reference to the file @file{INSTALL}, which
+should in turn contain an explanation of the installation procedure;
+
+@item a brief explanation of any unusual top-level directories or
+files, or other hints for readers to find their way around the source;
+
+@item a reference to the file which contains the copying conditions.
+The GNU GPL, if used, should be in a file called @file{COPYING}. If
+the GNU LGPL is used, it should be in a file called
+@file{COPYING.LESSER}.
+@end itemize
+
+Naturally, all the source files must be in the distribution. It is
+okay to include non-source files in the distribution along with the
+source files they are generated from, provided they are up-to-date
+with the source they are made from, and machine-independent, so that
+normal building of the distribution will never modify them. We
+commonly include non-source files produced by Autoconf, Automake,
+Bison, @code{flex}, @TeX{}, and @code{makeinfo}; this helps avoid
unnecessary dependencies between our distributions, so that users can
-install whichever packages they want to install.
+install whichever versions of whichever packages they like. Do not
+induce new dependencies on other software lightly.
Non-source files that might actually be modified by building and
installing the program should @strong{never} be included in the
distribution. So if you do distribute non-source files, always make
sure they are up to date when you make a new distribution.
-Make sure that the directory into which the distribution unpacks (as
-well as any subdirectories) are all world-writable (octal mode 777).
-This is so that old versions of @code{tar} which preserve the
-ownership and permissions of the files from the tar archive will be
-able to extract all the files even if the user is unprivileged.
-
-Make sure that all the files in the distribution are world-readable.
+Make sure that all the files in the distribution are world-readable, and
+that directories are world-readable and world-searchable (octal mode 755).
+We used to recommend that all directories in the distribution also be
+world-writable (octal mode 777), because ancient versions of @code{tar}
+would otherwise not cope when extracting the archive as an unprivileged
+user. That can easily lead to security issues when creating the archive,
+however, so now we recommend against that.
Don't include any symbolic links in the distribution itself. If the tar
file contains symbolic links, then people cannot even unpack it on
@chapter References to Non-Free Software and Documentation
@cindex references to non-free material
-A GNU program should not recommend use of any non-free program. We
+A GNU program should not recommend, promote, or grant legitimacy to
+the use of any non-free program. Proprietary software is a social and
+ethical problem, and our aim is to put an end to that problem. We
can't stop some people from writing proprietary programs, or stop
other people from using them, but we can and should refuse to
-advertise them to new potential customers. Proprietary software is a
-social and ethical problem, and the point of GNU is to solve that
-problem.
+advertise them to new potential customers, or to give the public the
+idea that their existence is ethical.
The GNU definition of free software is found on the GNU web site at
-@url{http://www.gnu.org/philosophy/free-sw.html}, and the definition
+@url{http://www.gnu.org/@/philosophy/@/free-sw.html}, and the definition
of free documentation is found at
-@url{http://www.gnu.org/philosophy/free-doc.html}. A list of
-important licenses and whether they qualify as free is in
-@url{http://www.gnu.org/@/licenses/@/license-list.html}. The terms
-``free'' and ``non-free'', used in this document, refer to that
-definition. If it is not clear whether a license qualifies as free
-under this definition, please ask the GNU Project by writing to
-@email{licensing@@gnu.org}. We will answer, and if the license is an
-important one, we will add it to the list.
+@url{http://www.gnu.org/@/philosophy/@/free-doc.html}. The terms ``free''
+and ``non-free'', used in this document, refer to those definitions.
+
+A list of important licenses and whether they qualify as free is in
+@url{http://www.gnu.org/@/licenses/@/license-list.html}. If it is not
+clear whether a license qualifies as free, please ask the GNU Project
+by writing to @email{licensing@@gnu.org}. We will answer, and if the
+license is an important one, we will add it to the list.
When a non-free program or system is well known, you can mention it in
passing---that is harmless, since users who might want to use it
thing. The goal should be that people already using the proprietary
program will get the advice they need about how to use your free
program with it, while people who don't already use the proprietary
-program will not see anything to lead them to take an interest in it.
+program will not see anything likely to lead them to take an interest
+in it.
If a non-free program or system is obscure in your program's domain,
your program should not mention or support it at all, since doing so
would tend to popularize the non-free program more than it popularizes
-your program. (You cannot hope to find many additional users among
-the users of Foobar if the users of Foobar are few.)
+your program. (You cannot hope to find many additional users for your
+program among the users of Foobar, if the existence of Foobar is not
+generally known among people who might want to use your program.)
Sometimes a program is free software in itself but depends on a
non-free platform in order to run. For instance, many Java programs
-depend on Sun's Java implementation, and won't run on the GNU Java
-Compiler (which does not yet have all the features) or won't run with
-the GNU Java libraries. To recommend that program is inherently to
-recommend the non-free platform as well; if you should not do the
-latter, then don't do the former.
+depend on some non-free Java libraries. To recommend or promote such
+a program is to promote the other programs it needs. This is why we
+are careful about listing Java programs in the Free Software
+Directory: we don't want to promote the non-free Java libraries.
+
+We hope this particular problem with Java will be gone by and by, as
+we replace the remaining non-free standard Java libraries with free
+software, but the general principle will remain the same: don't
+recommend, promote or legitimize programs that depend on non-free
+software to run.
+
+Some free programs strongly encourage the use of non-free software. A
+typical example is @command{mplayer}. It is free software in itself,
+and the free code can handle some kinds of files. However,
+@command{mplayer} recommends use of non-free codecs for other kinds of
+files, and users that install @command{mplayer} are very likely to
+install those codecs along with it. To recommend @command{mplayer}
+is, in effect, to promote use of the non-free codecs.
+
+Thus, you should not recommend programs that strongly encourage the
+use of non-free software. This is why we do not list
+@command{mplayer} in the Free Software Directory.
A GNU package should not refer the user to any non-free documentation
for free software. Free documentation that can be included in free
operating systems is essential for completing the GNU system, or any
-free operating system, so it is a major focus of the GNU Project; to
-recommend use of documentation that we are not allowed to use in GNU
-would weaken the impetus for the community to produce documentation
-that we can include. So GNU packages should never recommend non-free
+free operating system, so encouraging it is a priority; to recommend
+use of documentation that we are not allowed to include undermines the
+impetus for the community to produce documentation that we can
+include. So GNU packages should never recommend non-free
documentation.
By contrast, it is ok to refer to journal articles and textbooks in
the comments of a program for explanation of how it functions, even
-though they be non-free. This is because we don't include such things
-in the GNU system even if we are allowed to--they are outside the
-scope of an operating system project.
+though they are non-free. This is because we don't include such
+things in the GNU system even if they are free---they are outside the
+scope of what a software distribution needs to include.
Referring to a web site that describes or recommends a non-free
-program is in effect promoting that software, so please do not make
-links (or mention by name) web sites that contain such material. This
-policy is relevant particularly for the web pages for a GNU package.
-
-Following links from nearly any web site can lead to non-free
-software; this is an inescapable aspect of the nature of the web, and
-in itself is no objection to linking to a site. As long as the site
-does not itself recommend a non-free program, there is no need be
-concerned about the sites it links to for other reasons.
-
-Thus, for example, you should not make a link to AT&T's web site,
-because that recommends AT&T's non-free software packages; you should
-not make a link to a site that links to AT&T's site saying it is a
-place to get a non-free program; but if a site you want to link to
-refers to AT&T's web site in some other context (such as long-distance
-telephone service), that is not a problem.
-
-@node Copying This Manual
-@appendix Copying This Manual
-
-@menu
-* GNU Free Documentation License:: License for copying this manual
-@end menu
-
+program is promoting that program, so please do not make links to (or
+mention by name) web sites that contain such material. This policy is
+relevant particularly for the web pages for a GNU package.
+
+Following links from nearly any web site can lead eventually to
+non-free software; this is inherent in the nature of the web. So it
+makes no sense to criticize a site for having such links. As long as
+the site does not itself recommend a non-free program, there is no
+need to consider the question of the sites that it links to for other
+reasons.
+
+Thus, for example, you should not refer to AT&T's web site if that
+recommends AT&T's non-free software packages; you should not refer to
+a site that links to AT&T's site presenting it as a place to get some
+non-free program, because that link recommends and legitimizes the
+non-free program. However, that a site contains a link to AT&T's web
+site for some other purpose (such as long-distance telephone service)
+is not an objection against it.
+
+@node GNU Free Documentation License
+@appendix GNU Free Documentation License
+
+@cindex FDL, GNU Free Documentation License
@include fdl.texi
@node Index
time-stamp-start: "@set lastupdate "
time-stamp-end: "$"
time-stamp-format: "%:b %:d, %:y"
-compile-command: "make just-standards"
+compile-command: "cd work.s && make"
End:
projects / gnulib.git / blobdiff