File: standards.info, Node: Top, Next: Preface, Up: (dir)
GNU Coding Standards
********************
The GNU coding standards, last updated July 25, 2016.
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012,
2013, 2014, 2015, 2016 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 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
copy of the license is included in the section entitled "GNU Free
Documentation License".
* 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:: Mentioning non-free software or documentation.
* GNU Free Documentation License:: Copying and sharing this manual.
* Index::
File: standards.info, Node: Preface, Next: Legal Issues, Prev: Top, Up: Top
1 About the GNU Coding Standards
********************************
The GNU Coding Standards were written by Richard Stallman and other GNU
Project volunteers. Their purpose is to make the GNU system clean,
consistent, and easy to install. This document can also be read as a
guide to writing portable, robust and reliable programs. It focuses on
programs written in C, but many of the rules and principles are useful
even if you write in another programming language. The rules often
state reasons for writing in a certain way.
If you did not obtain this file directly from the GNU project and
recently, please check for a newer version. You can get the GNU Coding
Standards from the GNU web server in many different formats, including
the Texinfo source, PDF, HTML, DVI, plain text, and more, at:
<http://www.gnu.org/prep/standards/>;.
If you are maintaining an official GNU package, in addition to this
document, please read and follow the GNU maintainer information (*note
Contents: (maintain)Top.).
If you want to receive diffs for every change to these GNU documents,
join the mailing list 'gnustandards-commit AT gnu.org', via the web
interface at
<http://lists.gnu.org/mailman/listinfo/gnustandards-commit>;. Archives
are also available there.
Please send corrections or suggestions for this document to
<bug-standards AT 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
<http://savannah.gnu.org/projects/gnustandards>;.
These standards cover the minimum of what is important when writing a
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.
You should also set standards for your package on many questions not
addressed or not firmly specified here. The most important point is to
be self-consistent--try to stick to the conventions you pick, and try to
document them as much as possible. That way, your program will be more
maintainable by others.
The GNU Hello program serves as an example of how to follow the GNU
coding standards for a trivial program.
<http://www.gnu.org/software/hello/hello.html>;.
This release of the GNU Coding Standards was last updated July 25,
2016.
File: standards.info, Node: Legal Issues, Next: Design Advice, Prev: Preface, Up: Top
2 Keeping Free Software Free
****************************
This chapter discusses how you can make sure that GNU software 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.
File: standards.info, Node: Reading Non-Free Code, Next: Contributions, Up: Legal Issues
2.1 Referring to Proprietary Programs
=====================================
Don't in any circumstances refer to Unix source code for or during your
work on GNU! (Or to any other proprietary programs.)
If you have a vague recollection of the internals of a Unix program,
this does not absolutely mean you can't write an imitation of it, but do
try to organize the imitation internally along different lines, because
this is likely to make the details of the Unix version irrelevant and
dissimilar to your results.
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 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, on the contrary, emphasize simplicity instead of speed. For some
applications, the speed of today's computers makes simpler algorithms
adequate.
Or go for generality. For example, Unix programs often have static
tables or fixed-size strings, which make for arbitrary limits; use
dynamic allocation instead. Make sure your program handles NULs and
other funny characters in the input files. Add a programming language
for extensibility and write part of the program in that language.
Or turn some parts of the program into independently usable
libraries. Or use a simple garbage collector instead of tracking
precisely when to free memory, or use a new GNU facility such as
obstacks.
File: standards.info, Node: Contributions, Next: Trademarks, Prev: Reading Non-Free Code, Up: Legal Issues
2.2 Accepting Contributions
===========================
If the program you are working on is copyrighted by the Free Software
Foundation, then when someone else sends you a piece of code to add to
the program, we need legal papers to use it--just as we asked you to
sign papers initially. _Each_ person who makes a nontrivial
contribution to a program must sign some sort of legal papers in order
for us to have clear title to the program; the main author alone is not
enough.
So, before adding in any contributions from other people, please tell
us, so we can arrange to get the papers. Then wait until we tell you
that we have received the signed papers, before you actually use the
contribution.
This applies both before you release the program and afterward. If
you receive diffs to fix a bug, and they make significant changes, we
need legal papers for that change.
This also applies to comments and documentation files. For copyright
law, comments and code are just text. Copyright applies to all kinds of
text, so we need legal papers for all kinds.
We know it is frustrating to ask for legal papers; it's frustrating
for us as well. But if you don't wait, you are going out on a limb--for
example, what if the contributor's employer won't sign a disclaimer?
You might have to take that code out again!
You don't need papers for changes of a few lines here or there, since
they are not significant for copyright purposes. Also, you don't need
papers if all you get from the suggestion is some ideas, not actual code
which you use. For example, if someone sent you one implementation, but
you write a different implementation of the same idea, you don't need to
get papers.
The very worst thing is if you forget to tell us about the other
contributor. We could be very embarrassed in court some day as a
result.
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: *note (maintain)Legal Matters::.
File: standards.info, Node: Trademarks, Prev: Contributions, Up: Legal Issues
2.3 Trademarks
==============
Please do not include any trademark acknowledgements in GNU software
packages or documentation.
Trademark acknowledgements are the statements that such-and-such is a
trademark of so-and-so. The GNU Project has no objection to the basic
idea of trademarks, but these acknowledgements feel like kowtowing, and
there is no legal requirement for them, so we don't use them.
What is legally required, as regards other people's trademarks, is to
avoid using them in ways which a reader might reasonably understand as
naming or labeling our own programs or activities. For example, since
"Objective C" is (or at least was) a trademark, we made sure to say that
we provide a "compiler for the Objective C language" rather than an
"Objective C compiler". The latter would have been meant as a shorter
way of saying the former, but it does not explicitly state the
relationship, so it could be misinterpreted as using "Objective C" as a
label for the compiler rather than for the language.
Please don't use "win" as an abbreviation for Microsoft Windows in
GNU software or documentation. In hacker terminology, calling something
a "win" is a form of praise. If you wish to praise Microsoft Windows
when speaking on your own, by all means do so, but not in GNU software.
Usually we write the name "Windows" in full, but when brevity is very
important (as in file names and sometimes symbol names), we abbreviate
it to "w". For instance, the files and functions in Emacs that deal
with Windows start with 'w32'.
File: standards.info, Node: Design Advice, Next: Program Behavior, Prev: Legal Issues, Up: Top
3 General Program Design
************************
This chapter discusses some of the issues you should take into account
when designing your program.
* 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.
File: standards.info, Node: Source Language, Next: Compatibility, Up: Design Advice
3.1 Which Languages to Use
==========================
When you want to use a language that gets compiled and runs at high
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 Lisp, Scheme, Python, Ruby,
and Java, are OK too. Scheme, as implemented by GNU 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 (*note (guile)The
Emacs Thesis::).
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.
The standard extensibility interpreter for GNU software is Guile
(<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.
File: standards.info, Node: Compatibility, Next: Using Extensions, Prev: Source Language, Up: Design Advice
3.2 Compatibility with Other Implementations
============================================
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 POSIX if POSIX specifies their behavior.
When these standards conflict, it is useful to offer compatibility
modes for each of them.
Standard C and POSIX prohibit many kinds of extensions. Feel free to
make the extensions anyway, and include a '--ansi', '--posix', or
'--compatible' option to turn them off. However, if the extension has a
significant chance of breaking any real programs or scripts, then it is
not really upward compatible. So you should try to redesign its
interface to make it upward compatible.
Many GNU programs suppress extensions that conflict with POSIX if the
environment variable 'POSIXLY_CORRECT' is defined (even if it is defined
with a null value). Please make your program recognize this variable if
appropriate.
When a feature is used only by users (not by programs or command
files), and it is done poorly in Unix, feel free to replace it
completely with something totally different and better. (For example,
'vi' is replaced with Emacs.) But it is nice to offer a compatible
feature as well. (There is a free 'vi' clone, so we offer it.)
Additional useful features are welcome regardless of whether there is
any precedent for them.
File: standards.info, Node: Using Extensions, Next: Standard C, Prev: Compatibility, Up: Design Advice
3.3 Using Non-standard Features
===============================
Many GNU facilities that already exist support a number of convenient
extensions over the comparable Unix facilities. Whether to use these
extensions in implementing your program is a difficult question.
On the one hand, using the extensions can make a cleaner program. On
the other hand, people will not be able to build the program unless the
other GNU tools are available. This might cause the program to work on
fewer kinds of machines.
With some extensions, it might be easy to provide both alternatives.
For example, you can define functions with a "keyword" 'INLINE' and
define that as a macro to expand into either 'inline' or nothing,
depending on the compiler.
In general, perhaps it is best not to use the extensions if you can
straightforwardly do without them, but to use the extensions if they are
a big improvement.
An exception to this rule are the large, established programs (such
as Emacs) which run on a great variety of systems. Using GNU extensions
in such programs would make many users unhappy, so we don't do that.
Another exception is for programs that are used as part of
compilation: anything that must be compiled with other compilers in
order to bootstrap the GNU compilation facilities. If these require the
GNU compiler, then no one can compile them without having them installed
already. That would be extremely troublesome in certain cases.
File: standards.info, Node: Standard C, Next: Conditional Compilation, Prev: Using Extensions, Up: Design Advice
3.4 Standard C and Pre-Standard C
=================================
1989 Standard C is widespread enough now that it is ok to use its
features in programs. There is one exception: do not ever use the
"trigraph" feature of Standard C.
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.
To support pre-standard C, instead of writing function definitions in
standard prototype form,
int
foo (int x, int y)
...
write the definition in pre-standard style like this,
int
foo (x, y)
int x, y;
...
and use a separate declaration to specify the argument prototype:
int foo (int, int);
You need such a declaration anyway, in a header file, to get the
benefit of prototypes in all the files where the function is called.
And once you have the declaration, you normally lose nothing by writing
the function definition in the pre-standard style.
This technique does not work for integer types narrower than 'int'.
If you think of an argument as being of a type narrower than 'int',
declare it as 'int' instead.
There are a few special cases where this technique is hard to use.
For example, if a function argument needs to hold the system type
'dev_t', you run into trouble, because 'dev_t' is shorter than 'int' on
some machines; but you cannot use 'int' instead, because 'dev_t' is
wider than 'int' on some machines. There is no type you can safely use
on all machines in a non-standard definition. The only way to support
non-standard C and pass such an argument is to check the width of
'dev_t' using Autoconf and choose the argument type accordingly. This
may not be worth the trouble.
In order to support pre-standard compilers that do not recognize
prototypes, you may want to use a preprocessor macro like this:
/* Declare the prototype for a general external function. */
#if defined (__STDC__) || defined (WINDOWSNT)
#define P_(proto) proto
#else
#define P_(proto) ()
#endif
File: standards.info, Node: Conditional Compilation, Prev: Standard C, Up: Design Advice
3.5 Conditional Compilation
===========================
When supporting configuration options already known when building your
program we prefer using 'if (... )' over conditional compilation, as in
the former case the compiler is able to perform more extensive checking
of all possible code paths.
For example, please write
if (HAS_FOO)
...
else
...
instead of:
#ifdef HAS_FOO
...
#else
...
#endif
A modern compiler such as GCC will generate exactly the same code in
both cases, and we have been using similar techniques with good success
in several projects. Of course, the former method assumes that
'HAS_FOO' is defined as either 0 or 1.
While this is not a silver bullet solving all portability problems,
and is not always appropriate, following this policy would have saved
GCC developers many hours, or even days, per year.
In the case of function-like macros like 'REVERSIBLE_CC_MODE' in GCC
which cannot be simply used in 'if (...)' statements, there is an easy
workaround. Simply introduce another macro 'HAS_REVERSIBLE_CC_MODE' as
in the following example:
#ifdef REVERSIBLE_CC_MODE
#define HAS_REVERSIBLE_CC_MODE 1
#else
#define HAS_REVERSIBLE_CC_MODE 0
#endif
File: standards.info, Node: Program Behavior, Next: Writing C, Prev: Design Advice, Up: Top
4 Program Behavior for All Programs
***********************************
This chapter describes conventions for writing robust software. It also
describes general standards for error messages, the command line
interface, and how libraries should behave.
* 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.
* 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.
File: standards.info, Node: Non-GNU Standards, Next: Semantics, Up: Program Behavior
4.1 Non-GNU Standards
=====================
The GNU Project regards standards published by other organizations as
suggestions, not orders. We consider those standards, but we do not
"obey" them. In developing a GNU program, you should implement an
outside standard's specifications when that makes the GNU system better
overall in an objective sense. When it doesn't, you shouldn't.
In most cases, following published standards is convenient for
users--it means that their programs or scripts will work more portably.
For instance, GCC implements nearly all the features of Standard C as
specified by that standard. C program developers would be unhappy if it
did not. And GNU utilities mostly follow specifications of POSIX.2;
shell script writers and users would be unhappy if our programs were
incompatible.
But we do not follow either of these specifications rigidly, and
there are specific points on which we decided not to follow them, so as
to make the GNU system better for users.
For instance, Standard C says that nearly all extensions to C are
prohibited. How silly! GCC implements many extensions, some of which
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 '--pedantic', which was implemented only so that 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 'df' and 'du' must output sizes by default in
units of 512 bytes. What users want is units of 1k, so that is what we
do by default. If you want the ridiculous behavior "required" by POSIX,
you must set the environment variable 'POSIXLY_CORRECT' (which was
originally going to be named 'POSIX_ME_HARDER').
GNU utilities also depart from the letter of the POSIX.2
specification when they support long-named command-line options, and
intermixing options with ordinary arguments. This minor incompatibility
with 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".
File: standards.info, Node: Semantics, Next: Libraries, Prev: Non-GNU Standards, Up: Program Behavior
4.2 Writing Robust Programs
===========================
Avoid arbitrary limits on the length or number of _any_ data structure,
including file names, lines, files, and symbols, by allocating all data
structures dynamically. In most Unix utilities, "long lines are
silently truncated". This is not acceptable in a GNU utility.
Utilities reading files should not drop NUL characters, or any other
nonprinting characters. Programs should work properly with multibyte
character encodings, such as UTF-8. You can use libiconv to deal with a
range of encodings.
Check every system call for an error return, unless you know you wish
to ignore errors. Include the system error text (from 'strerror', or
equivalent) in _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 call to 'malloc' or 'realloc' to see if it returned
'NULL'. Check 'realloc' even if you are making the block smaller; in a
system that rounds block sizes to a power of 2, 'realloc' may get a
different block if you ask for less space.
You must expect 'free' to alter the contents of the block that was
freed. Anything you want to fetch from the block, you must fetch before
calling 'free'.
If 'malloc' fails in a noninteractive program, make that a fatal
error. In an interactive program (one that reads commands from the
user), it is better to abort the command and return to the command
reader loop. This allows the user to kill other processes to free up
virtual memory, and then try the command again.
Use 'getopt_long' to decode arguments, unless the argument syntax
makes this unreasonable.
When static storage is to be written in during program execution, use
explicit C code to initialize it. This way, restarting the program
(without reloading it), or part of it, will reinitialize those
variables. Reserve C initialized declarations for data that will not be
changed.
Try to avoid low-level interfaces to obscure Unix data structures
(such as file directories, utmp, or the layout of kernel memory), since
these are less likely to work compatibly. If you need to find all the
files in a directory, use 'readdir' or some other high-level interface.
These are supported compatibly by GNU.
The preferred signal handling facilities are the BSD variant of
'signal', and the POSIX 'sigaction' function; the alternative USG
'signal' interface is an inferior design.
Nowadays, using the POSIX signal functions may be the easiest way to
make a program portable. If you use 'signal', then on GNU/Linux systems
running GNU libc version 1, you should include 'bsd/signal.h' instead of
'signal.h', so as to get BSD behavior. It is up to you whether to
support systems where 'signal' has only the USG behavior, or give up on
them.
In error checks that detect "impossible" conditions, just abort.
There is usually no point in printing any message. These checks
indicate the existence of bugs. Whoever wants to fix the bugs will have
to read the source code and run a debugger. So explain the problem with
comments in the source. The relevant data will be in variables, which
are easy to examine with the debugger, so there is no point moving them
elsewhere.
Do not use a count of errors as the exit status for a program. _That
does not work_, because exit status values are limited to 8 bits (0
through 255). A single run of the program might have 256 errors; if you
try to return 256 as the exit status, the parent process will see 0 as
the status, and it will appear that the program succeeded.
If you make temporary files, check the 'TMPDIR' environment variable;
if that variable is defined, use the specified directory instead of
'/tmp'.
In addition, be aware that there is a possible security problem when
creating temporary files in world-writable directories. In C, you can
avoid this problem by creating temporary files in this manner:
fd = open (filename, O_WRONLY | O_CREAT | O_EXCL, 0600);
or by using the 'mkstemps' function from Gnulib (*note
(gnulib)mkstemps::).
In bash, use 'set -C' (long name 'noclobber') to avoid this problem.
In addition, the 'mktemp' utility is a more general solution for
creating temporary files from shell scripts (*note (coreutils)mktemp
invocation::).
File: standards.info, Node: Libraries, Next: Errors, Prev: Semantics, Up: Program Behavior
4.3 Library Behavior
====================
Try to make library functions reentrant. If they need to do dynamic
storage allocation, at least try to avoid any nonreentrancy aside from
that of 'malloc' itself.
Here are certain name conventions for libraries, to avoid name
conflicts.
Choose a name prefix for the library, more than two characters long.
All external function and variable names should start with this prefix.
In addition, there should only be one of these in any given library
member. This usually means putting each one in a separate source file.
An exception can be made when two external symbols are always used
together, so that no reasonable program could use one without the other;
then they can both go in the same file.
External symbols that are not documented entry points for the user
should have names beginning with '_'. The '_' should be followed by the
chosen name prefix for the library, to prevent collisions with other
libraries. These can go in the same files with user entry points if you
like.
Static functions and variables can be used as you like and need not
fit any naming convention.
File: standards.info, Node: Errors, Next: User Interfaces, Prev: Libraries, Up: Program Behavior
4.4 Formatting Error Messages
=============================
Error messages from compilers should look like this:
SOURCEFILE:LINENO: MESSAGE
If you want to mention the column number, use one of these formats:
SOURCEFILE:LINENO:COLUMN: MESSAGE
SOURCEFILE:LINENO.COLUMN: MESSAGE
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. For non-ASCII
characters, Unicode character widths should be used when in a UTF-8
locale; GNU libc and GNU gnulib provide suitable '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 avoid redundant information such as a duplicate line number. Here
are the possible formats:
SOURCEFILE:LINE1.COLUMN1-LINE2.COLUMN2: MESSAGE
SOURCEFILE:LINE1.COLUMN1-COLUMN2: MESSAGE
SOURCEFILE:LINE1-LINE2: MESSAGE
When an error is spread over several files, you can use this format:
FILE1:LINE1.COLUMN1-FILE2:LINE2.COLUMN2: MESSAGE
Error messages from other noninteractive programs should look like
this:
PROGRAM:SOURCEFILE:LINENO: MESSAGE
when there is an appropriate source file, or like this:
PROGRAM: MESSAGE
when there is no relevant source file.
If you want to mention the column number, use this format:
PROGRAM:SOURCEFILE:LINENO:COLUMN: MESSAGE
In an interactive program (one that is reading commands from a
terminal), it is better not to include the program name in an error
message. The place to indicate which program is running is in the
prompt or with the screen layout. (When the same program runs with
input from a source other than a terminal, it is not interactive and
would do best to print error messages using the noninteractive style.)
The string MESSAGE should not begin with a capital letter when it
follows a program name and/or file name, because that isn't the
beginning of a sentence. (The sentence conceptually starts at the
beginning of the line.) Also, it should not end with a period.
Error messages from interactive programs, and other messages such as
usage messages, should start with a capital letter. But they should not
end with a period.
File: standards.info, Node: User Interfaces, Next: Graphical Interfaces, Prev: Errors, Up: Program Behavior
4.5 Standards for Interfaces Generally
======================================
Please don't make the behavior of a utility depend on the name used to
invoke it. It is useful sometimes to make a link to a utility with a
different name, and that should not change what it does.
Instead, use a run time option or a compilation switch or both to
select among the alternate behaviors. You can also build two versions
of the program, with different names and different default behaviors.
Likewise, please don't make the behavior of a command-line program
depend on the type of output device it gets as standard output or
standard input. Device independence is an important principle of the
system's design; do not compromise it merely to save someone from typing
an option now and then. (Variation in error message syntax when using a
terminal is ok, because that is a side issue that people do not depend
on.)
If you think one behavior is most useful when the output is to a
terminal, and another is most useful when the output is a file or a
pipe, then it is usually best to make the default behavior the one that
is useful with output to a terminal, and have an option for the other
behavior. You can also build two different versions of the program with
different names.
There is an exception for programs whose output in certain cases is
binary data. Sending such output to a terminal is useless and can cause
trouble. If such a program normally sends its output to stdout, it
should detect, in these cases, when the output is a terminal and give an
error message instead. The '-f' option should override this exception,
thus permitting the output to go to the terminal.
Compatibility requires certain programs to depend on the type of
output device. It would be disastrous if 'ls' or 'sh' did not do so in
the way all users expect. In some of these cases, we supplement the
program with a preferred alternate version that does not depend on the
output device type. For example, we provide a 'dir' program much like
'ls' except that its default output format is always multi-column
format.
File: standards.info, Node: Graphical Interfaces, Next: Command-Line Interfaces, Prev: User Interfaces, Up: Program Behavior
4.6 Standards for Graphical Interfaces
======================================
When you write a program that provides a graphical user interface,
please make it work with the X Window System, using the GTK+ toolkit or
the GNUstep 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.
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.
Please make your program interoperate with access technology such as
screen readers (see
<http://www.gnu.org/accessibility/accessibility.html>;). This should be
automatic if you use GTK+.
File: standards.info, Node: Command-Line Interfaces, Next: Dynamic Plug-In Interfaces, Prev: Graphical Interfaces, Up: Program Behavior
4.7 Standards for Command Line Interfaces
=========================================
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 'getopt' to
parse them. Note that the GNU version of 'getopt' will normally permit
options anywhere among the arguments unless the special argument '--' is
used. This is not what POSIX specifies; it is a GNU extension.
Please define long-named options that are equivalent to the
single-letter Unix-style options. We hope to make GNU more user
friendly this way. This is easy to do with the GNU function
'getopt_long'.
One of the advantages of long-named options is that they can be
consistent from program to program. For example, users should be able
to expect the "verbose" option of any GNU program which has one, to be
spelled precisely '--verbose'. To achieve this uniformity, look at the
table of common long-option names when you choose the option names for
your program (*note Option Table::).
It is usually a good idea for file names given as ordinary arguments
to be input files only; any output files would be specified using
options (preferably '-o' or '--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 idiosyncrasies for users to remember.
All programs should support two standard options: '--version' and
'--help'. CGI programs should accept these as command-line options, and
also if given as the 'PATH_INFO'; for instance, visiting
'http://example.org/p.cgi/--help' in a browser should output the same
information as invoking 'p.cgi --help' from the command line.
* Menu:
* --version:: The standard output for -version.
* --help:: The standard output for -help.
File: standards.info, Node: --version, Next: --help, Up: Command-Line Interfaces
4.7.1 '--version'
-----------------
The standard '--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.
The first line is meant to be easy for a program to parse; the
version number proper starts after the last space. In addition, it
contains the canonical name for this program, in this format:
GNU Emacs 19.30
The program's name should be a constant string; _don't_ compute it from
'argv[0]'. The idea is to state the standard or canonical name for the
program, not its file name. There are other ways to find out the
precise file name where a command is found in 'PATH'.
If the program is a subsidiary part of a larger package, mention the
package name in parentheses, like this:
emacsserver (GNU Emacs) 19.30
If the package has a version number which is different from this
program's version number, you can mention the package version number
just before the close-parenthesis.
If you _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
the first line.
Please do not mention all of the libraries that the program uses
"just for completeness"--that would produce a lot of unhelpful clutter.
Please mention library version numbers only if you find in practice that
they are very important to you in debugging.
The following line, after the version number line or lines, should be
a copyright notice. If more than one copyright notice is called for,
put each on a separate line.
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:
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.
You should adapt this to your program, of course, filling in the
proper year, copyright holder, name of program, and the references to
distribution terms, and changing the rest of the wording as necessary.
This copyright notice only needs to mention the most recent year in
which changes were made--there's no need to list the years for previous
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;
*note (maintain)Copyright Notices::.)
Translations of the above lines must preserve the validity of the
copyright notices (*note Internationalization::). If the translation's
character set supports it, the '(C)' should be replaced with the
copyright symbol, as follows:
(the official copyright symbol, which is the letter C in a circle);
Write the word "Copyright" exactly like that, in English. Do not
translate it into another language. International treaties recognize
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 'vVERSION[+]', meaning that
particular version, or later versions with the '+', as shown above. In
the case of a GNU license, _always_ indicate the permitted versions in
this way.
In the case of exceptions for extra permissions with the GPL, we use
'/' for a separator; the version number can follow the license
abbreviation as usual, as in the examples below.
GPL
GNU General Public License, <http://www.gnu.org/licenses/gpl.html>;.
LGPL
GNU Lesser General Public License,
<http://www.gnu.org/licenses/lgpl.html>;.
GPL/Ada
GNU GPL with the exception for Ada.
Apache
The Apache Software Foundation license,
<http://www.apache.org/licenses>;.
Artistic
The Artistic license used for Perl,
<http://dev.perl.org/licenses/artistic.html>;.
Expat
The Expat license, <http://www.jclark.com/xml/copying.txt>;.
MPL
The Mozilla Public License, <http://www.mozilla.org/MPL/>;.
OBSD
The original (4-clause) BSD license, incompatible with the GNU GPL
<http://www.xfree86.org/3.3.6/COPYRIGHT2.html#6>;.
PHP
The license used for PHP, <http://www.php.net/license/>;.
public domain
The non-license that is being in the public domain,
<http://www.gnu.org/licenses/license-list.html#PublicDomain>;.
Python
The license for Python,
<http://directory.fsf.org/wiki?title=License:Python2.0.1>.
RBSD
The revised (3-clause) BSD, compatible with the GNU GPL,
<http://www.xfree86.org/3.3.6/COPYRIGHT2.html#5>;.
X11
The simple non-copyleft license used for most versions of the X
Window System, <http://www.xfree86.org/3.3.6/COPYRIGHT2.html#3>;.
Zlib
The license for Zlib, <http://www.gzip.org/zlib/zlib_license.html>;.
More information about these licenses and many more are on the GNU
licensing web pages, <http://www.gnu.org/licenses/license-list.html>;.
File: standards.info, Node: --help, Prev: --version, Up: Command-Line Interfaces
4.7.2 '--help'
--------------
The standard '--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.
Near the end of the '--help' option's output, please place lines
giving the email address for bug reports, the package's home page
(normally 'http://www.gnu.org/software/PKG', and the general page for
help using GNU programs. The format should be like this:
Report bugs to: MAILING-ADDRESS
PKG home page: <http://www.gnu.org/software/PKG/>;
General help using GNU software: <http://www.gnu.org/gethelp/>;
It is ok to mention other appropriate mailing lists and web pages.
File: standards.info, Node: Dynamic Plug-In Interfaces, Next: Option Table, Prev: Command-Line Interfaces, Up: Program Behavior
4.8 Standards for Dynamic Plug-in Interfaces
============================================
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.
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 'plugin_is_GPL_compatible', thus
asserting that the plug-in is released under a GPL-compatible license
(*note Plugins: (gccint)Plugins.).
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.
File: standards.info, Node: Option Table, Next: OID Allocations, Prev: Dynamic Plug-In Interfaces, Up: Program Behavior
4.9 Table of Long Options
=========================
Here is a table of long options used by GNU programs. It is surely
incomplete, but we aim to list all the options that a new program might
want to be compatible with. If you use names not already in the table,
please send <bug-standards AT gnu.org> a list of them, with their meanings,
so we can update the table.
'after-date'
'-N' in 'tar'.
'all'
'-a' in 'du', 'ls', 'nm', 'stty', 'uname', and 'unexpand'.
'all-text'
'-a' in 'diff'.
'almost-all'
'-A' in 'ls'.
'append'
'-a' in 'etags', 'tee', 'time'; '-r' in 'tar'.
'archive'
'-a' in 'cp'.
'archive-name'
'-n' in 'shar'.
'arglength'
'-l' in 'm4'.
'ascii'
'-a' in 'diff'.
'assign'
'-v' in 'gawk'.
'assume-new'
'-W' in 'make'.
'assume-old'
'-o' in 'make'.
'auto-check'
'-a' in 'recode'.
'auto-pager'
'-a' in 'wdiff'.
'auto-reference'
'-A' in 'ptx'.
'avoid-wraps'
'-n' in 'wdiff'.
'background'
For server programs, run in the background.
'backward-search'
'-B' in 'ctags'.
'basename'
'-f' in 'shar'.
'batch'
Used in GDB.
'baud'
Used in GDB.
'before'
'-b' in 'tac'.
'binary'
'-b' in 'cpio' and 'diff'.
'bits-per-code'
'-b' in 'shar'.
'block-size'
Used in 'cpio' and 'tar'.
'blocks'
'-b' in 'head' and 'tail'.
'break-file'
'-b' in 'ptx'.
'brief'
Used in various programs to make output shorter.
'bytes'
'-c' in 'head', 'split', and 'tail'.
'c++'
'-C' in 'etags'.
'catenate'
'-A' in 'tar'.
'cd'
Used in various programs to specify the directory to use.
'changes'
'-c' in 'chgrp' and 'chown'.
'classify'
'-F' in 'ls'.
'colons'
'-c' in 'recode'.
'command'
'-c' in 'su'; '-x' in GDB.
'compare'
'-d' in 'tar'.
'compat'
Used in 'gawk'.
'compress'
'-Z' in 'tar' and 'shar'.
'concatenate'
'-A' in 'tar'.
'confirmation'
'-w' in 'tar'.
'context'
Used in 'diff'.
'copyleft'
'-W copyleft' in 'gawk'.
'copyright'
'-C' in 'ptx', 'recode', and 'wdiff'; '-W copyright' in 'gawk'.
'core'
Used in GDB.
'count'
'-q' in 'who'.
'count-links'
'-l' in 'du'.
'create'
Used in 'tar' and 'cpio'.
'cut-mark'
'-c' in 'shar'.
'cxref'
'-x' in 'ctags'.
'date'
'-d' in 'touch'.
'debug'
'-d' in 'make' and 'm4'; '-t' in Bison.
'define'
'-D' in 'm4'.
'defines'
'-d' in Bison and 'ctags'.
'delete'
'-D' in 'tar'.
'dereference'
'-L' in 'chgrp', 'chown', 'cpio', 'du', 'ls', and 'tar'.
'dereference-args'
'-D' in 'du'.
'device'
Specify an I/O device (special file name).
'diacritics'
'-d' in 'recode'.
'dictionary-order'
'-d' in 'look'.
'diff'
'-d' in 'tar'.
'digits'
'-n' in 'csplit'.
'directory'
Specify the directory to use, in various programs. In 'ls', it
means to show directories themselves rather than their contents.
In 'rm' and 'ln', it means to not treat links to directories
specially.
'discard-all'
'-x' in 'strip'.
'discard-locals'
'-X' in 'strip'.
'dry-run'
'-n' in 'make'.
'ed'
'-e' in 'diff'.
'elide-empty-files'
'-z' in 'csplit'.
'end-delete'
'-x' in 'wdiff'.
'end-insert'
'-z' in 'wdiff'.
'entire-new-file'
'-N' in 'diff'.
'environment-overrides'
'-e' in 'make'.
'eof'
'-e' in 'xargs'.
'epoch'
Used in GDB.
'error-limit'
Used in 'makeinfo'.
'error-output'
'-o' in 'm4'.
'escape'
'-b' in 'ls'.
'exclude-from'
'-X' in 'tar'.
'exec'
Used in GDB.
'exit'
'-x' in 'xargs'.
'exit-0'
'-e' in 'unshar'.
'expand-tabs'
'-t' in 'diff'.
'expression'
'-e' in 'sed'.
'extern-only'
'-g' in 'nm'.
'extract'
'-i' in 'cpio'; '-x' in 'tar'.
'faces'
'-f' in 'finger'.
'fast'
'-f' in 'su'.
'fatal-warnings'
'-E' in 'm4'.
'file'
'-f' in 'gawk', 'info', 'make', 'mt', 'sed', and 'tar'.
'field-separator'
'-F' in 'gawk'.
'file-prefix'
'-b' in Bison.
'file-type'
'-F' in 'ls'.
'files-from'
'-T' in 'tar'.
'fill-column'
Used in 'makeinfo'.
'flag-truncation'
'-F' in 'ptx'.
'fixed-output-files'
'-y' in Bison.
'follow'
'-f' in 'tail'.
'footnote-style'
Used in 'makeinfo'.
'force'
'-f' in 'cp', 'ln', 'mv', and 'rm'.
'force-prefix'
'-F' in 'shar'.
'foreground'
For server programs, run in the foreground; in other words, don't
do anything special to run the server in the background.
'format'
Used in 'ls', 'time', and 'ptx'.
'freeze-state'
'-F' in 'm4'.
'fullname'
Used in GDB.
'gap-size'
'-g' in 'ptx'.
'get'
'-x' in 'tar'.
'graphic'
'-i' in 'ul'.
'graphics'
'-g' in 'recode'.
'group'
'-g' in 'install'.
'gzip'
'-z' in 'tar' and 'shar'.
'hashsize'
'-H' in 'm4'.
'header'
'-h' in 'objdump' and 'recode'
'heading'
'-H' in 'who'.
'help'
Used to ask for brief usage information.
'here-delimiter'
'-d' in 'shar'.
'hide-control-chars'
'-q' in 'ls'.
'html'
In 'makeinfo', output HTML.
'idle'
'-u' in 'who'.
'ifdef'
'-D' in 'diff'.
'ignore'
'-I' in 'ls'; '-x' in 'recode'.
'ignore-all-space'
'-w' in 'diff'.
'ignore-backups'
'-B' in 'ls'.
'ignore-blank-lines'
'-B' in 'diff'.
'ignore-case'
'-f' in 'look' and 'ptx'; '-i' in 'diff' and 'wdiff'.
'ignore-errors'
'-i' in 'make'.
'ignore-file'
'-i' in 'ptx'.
'ignore-indentation'
'-I' in 'etags'.
'ignore-init-file'
'-f' in Oleo.
'ignore-interrupts'
'-i' in 'tee'.
'ignore-matching-lines'
'-I' in 'diff'.
'ignore-space-change'
'-b' in 'diff'.
'ignore-zeros'
'-i' in 'tar'.
'include'
'-i' in 'etags'; '-I' in 'm4'.
'include-dir'
'-I' in 'make'.
'incremental'
'-G' in 'tar'.
'info'
'-i', '-l', and '-m' in Finger.
'init-file'
In some programs, specify the name of the file to read as the
user's init file.
'initial'
'-i' in 'expand'.
'initial-tab'
'-T' in 'diff'.
'inode'
'-i' in 'ls'.
'interactive'
'-i' in 'cp', 'ln', 'mv', 'rm'; '-e' in 'm4'; '-p' in 'xargs'; '-w'
in 'tar'.
'intermix-type'
'-p' in 'shar'.
'iso-8601'
Used in 'date'
'jobs'
'-j' in 'make'.
'just-print'
'-n' in 'make'.
'keep-going'
'-k' in 'make'.
'keep-files'
'-k' in 'csplit'.
'kilobytes'
'-k' in 'du' and 'ls'.
'language'
'-l' in 'etags'.
'less-mode'
'-l' in 'wdiff'.
'level-for-gzip'
'-g' in 'shar'.
'line-bytes'
'-C' in 'split'.
'lines'
Used in 'split', 'head', and 'tail'.
'link'
'-l' in 'cpio'.
'lint'
'lint-old'
Used in 'gawk'.
'list'
'-t' in 'cpio'; '-l' in 'recode'.
'list'
'-t' in 'tar'.
'literal'
'-N' in 'ls'.
'load-average'
'-l' in 'make'.
'login'
Used in 'su'.
'machine'
Used in 'uname'.
'macro-name'
'-M' in 'ptx'.
'mail'
'-m' in 'hello' and 'uname'.
'make-directories'
'-d' in 'cpio'.
'makefile'
'-f' in 'make'.
'mapped'
Used in GDB.
'max-args'
'-n' in 'xargs'.
'max-chars'
'-n' in 'xargs'.
'max-lines'
'-l' in 'xargs'.
'max-load'
'-l' in 'make'.
'max-procs'
'-P' in 'xargs'.
'mesg'
'-T' in 'who'.
'message'
'-T' in 'who'.
'minimal'
'-d' in 'diff'.
'mixed-uuencode'
'-M' in 'shar'.
'mode'
'-m' in 'install', 'mkdir', and 'mkfifo'.
'modification-time'
'-m' in 'tar'.
'multi-volume'
'-M' in 'tar'.
'name-prefix'
'-a' in Bison.
'nesting-limit'
'-L' in 'm4'.
'net-headers'
'-a' in 'shar'.
'new-file'
'-W' in 'make'.
'no-builtin-rules'
'-r' in 'make'.
'no-character-count'
'-w' in 'shar'.
'no-check-existing'
'-x' in 'shar'.
'no-common'
'-3' in 'wdiff'.
'no-create'
'-c' in 'touch'.
'no-defines'
'-D' in 'etags'.
'no-deleted'
'-1' in 'wdiff'.
'no-dereference'
'-d' in 'cp'.
'no-inserted'
'-2' in 'wdiff'.
'no-keep-going'
'-S' in 'make'.
'no-lines'
'-l' in Bison.
'no-piping'
'-P' in 'shar'.
'no-prof'
'-e' in 'gprof'.
'no-regex'
'-R' in 'etags'.
'no-sort'
'-p' in 'nm'.
'no-splash'
Don't print a startup splash screen.
'no-split'
Used in 'makeinfo'.
'no-static'
'-a' in 'gprof'.
'no-time'
'-E' in 'gprof'.
'no-timestamp'
'-m' in 'shar'.
'no-validate'
Used in 'makeinfo'.
'no-wait'
Used in 'emacsclient'.
'no-warn'
Used in various programs to inhibit warnings.
'node'
'-n' in 'info'.
'nodename'
'-n' in 'uname'.
'nonmatching'
'-f' in 'cpio'.
'nstuff'
'-n' in 'objdump'.
'null'
'-0' in 'xargs'.
'number'
'-n' in 'cat'.
'number-nonblank'
'-b' in 'cat'.
'numeric-sort'
'-n' in 'nm'.
'numeric-uid-gid'
'-n' in 'cpio' and 'ls'.
'nx'
Used in GDB.
'old-archive'
'-o' in 'tar'.
'old-file'
'-o' in 'make'.
'one-file-system'
'-l' in 'tar', 'cp', and 'du'.
'only-file'
'-o' in 'ptx'.
'only-prof'
'-f' in 'gprof'.
'only-time'
'-F' in 'gprof'.
'options'
'-o' in 'getopt', 'fdlist', 'fdmount', 'fdmountd', and 'fdumount'.
'output'
In various programs, specify the output file name.
'output-prefix'
'-o' in 'shar'.
'override'
'-o' in 'rm'.
'overwrite'
'-c' in 'unshar'.
'owner'
'-o' in 'install'.
'paginate'
'-l' in 'diff'.
'paragraph-indent'
Used in 'makeinfo'.
'parents'
'-p' in 'mkdir' and 'rmdir'.
'pass-all'
'-p' in 'ul'.
'pass-through'
'-p' in 'cpio'.
'port'
'-P' in 'finger'.
'portability'
'-c' in 'cpio' and 'tar'.
'posix'
Used in 'gawk'.
'prefix-builtins'
'-P' in 'm4'.
'prefix'
'-f' in 'csplit'.
'preserve'
Used in 'tar' and 'cp'.
'preserve-environment'
'-p' in 'su'.
'preserve-modification-time'
'-m' in 'cpio'.
'preserve-order'
'-s' in 'tar'.
'preserve-permissions'
'-p' in 'tar'.
'print'
'-l' in 'diff'.
'print-chars'
'-L' in 'cmp'.
'print-data-base'
'-p' in 'make'.
'print-directory'
'-w' in 'make'.
'print-file-name'
'-o' in 'nm'.
'print-symdefs'
'-s' in 'nm'.
'printer'
'-p' in 'wdiff'.
'prompt'
'-p' in 'ed'.
'proxy'
Specify an HTTP proxy.
'query-user'
'-X' in 'shar'.
'question'
'-q' in 'make'.
'quiet'
Used in many programs to inhibit the usual output. Every program
accepting '--quiet' should accept '--silent' as a synonym.
'quiet-unshar'
'-Q' in 'shar'
'quote-name'
'-Q' in 'ls'.
'rcs'
'-n' in 'diff'.
're-interval'
Used in 'gawk'.
'read-full-blocks'
'-B' in 'tar'.
'readnow'
Used in GDB.
'recon'
'-n' in 'make'.
'record-number'
'-R' in 'tar'.
'recursive'
Used in 'chgrp', 'chown', 'cp', 'ls', 'diff', and 'rm'.
'reference'
'-r' in 'touch'.
'references'
'-r' in 'ptx'.
'regex'
'-r' in 'tac' and 'etags'.
'release'
'-r' in 'uname'.
'reload-state'
'-R' in 'm4'.
'relocation'
'-r' in 'objdump'.
'rename'
'-r' in 'cpio'.
'replace'
'-i' in 'xargs'.
'report-identical-files'
'-s' in 'diff'.
'reset-access-time'
'-a' in 'cpio'.
'reverse'
'-r' in 'ls' and 'nm'.
'reversed-ed'
'-f' in 'diff'.
'right-side-defs'
'-R' in 'ptx'.
'same-order'
'-s' in 'tar'.
'same-permissions'
'-p' in 'tar'.
'save'
'-g' in 'stty'.
'se'
Used in GDB.
'sentence-regexp'
'-S' in 'ptx'.
'separate-dirs'
'-S' in 'du'.
'separator'
'-s' in 'tac'.
'sequence'
Used by 'recode' to chose files or pipes for sequencing passes.
'shell'
'-s' in 'su'.
'show-all'
'-A' in 'cat'.
'show-c-function'
'-p' in 'diff'.
'show-ends'
'-E' in 'cat'.
'show-function-line'
'-F' in 'diff'.
'show-tabs'
'-T' in 'cat'.
'silent'
Used in many programs to inhibit the usual output. Every program
accepting '--silent' should accept '--quiet' as a synonym.
'size'
'-s' in 'ls'.
'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 non-privileged process, a server that normally
needs a reserved port number.
'sort'
Used in 'ls'.
'source'
'-W source' in 'gawk'.
'sparse'
'-S' in 'tar'.
'speed-large-files'
'-H' in 'diff'.
'split-at'
'-E' in 'unshar'.
'split-size-limit'
'-L' in 'shar'.
'squeeze-blank'
'-s' in 'cat'.
'start-delete'
'-w' in 'wdiff'.
'start-insert'
'-y' in 'wdiff'.
'starting-file'
Used in 'tar' and 'diff' to specify which file within a directory
to start processing with.
'statistics'
'-s' in 'wdiff'.
'stdin-file-list'
'-S' in 'shar'.
'stop'
'-S' in 'make'.
'strict'
'-s' in 'recode'.
'strip'
'-s' in 'install'.
'strip-all'
'-s' in 'strip'.
'strip-debug'
'-S' in 'strip'.
'submitter'
'-s' in 'shar'.
'suffix'
'-S' in 'cp', 'ln', 'mv'.
'suffix-format'
'-b' in 'csplit'.
'sum'
'-s' in 'gprof'.
'summarize'
'-s' in 'du'.
'symbolic'
'-s' in 'ln'.
'symbols'
Used in GDB and 'objdump'.
'synclines'
'-s' in 'm4'.
'sysname'
'-s' in 'uname'.
'tabs'
'-t' in 'expand' and 'unexpand'.
'tabsize'
'-T' in 'ls'.
'terminal'
'-T' in 'tput' and 'ul'. '-t' in 'wdiff'.
'text'
'-a' in 'diff'.
'text-files'
'-T' in 'shar'.
'time'
Used in 'ls' and 'touch'.
'timeout'
Specify how long to wait before giving up on some operation.
'to-stdout'
'-O' in 'tar'.
'total'
'-c' in 'du'.
'touch'
'-t' in 'make', 'ranlib', and 'recode'.
'trace'
'-t' in 'm4'.
'traditional'
'-t' in 'hello'; '-W traditional' in 'gawk'; '-G' in 'ed', 'm4',
and 'ptx'.
'tty'
Used in GDB.
'typedefs'
'-t' in 'ctags'.
'typedefs-and-c++'
'-T' in 'ctags'.
'typeset-mode'
'-t' in 'ptx'.
'uncompress'
'-z' in 'tar'.
'unconditional'
'-u' in 'cpio'.
'undefine'
'-U' in 'm4'.
'undefined-only'
'-u' in 'nm'.
'update'
'-u' in 'cp', 'ctags', 'mv', 'tar'.
'usage'
Used in 'gawk'; same as '--help'.
'uuencode'
'-B' in 'shar'.
'vanilla-operation'
'-V' in 'shar'.
'verbose'
Print more information about progress. Many programs support this.
'verify'
'-W' in 'tar'.
'version'
Print the version number.
'version-control'
'-V' in 'cp', 'ln', 'mv'.
'vgrind'
'-v' in 'ctags'.
'volume'
'-V' in 'tar'.
'what-if'
'-W' in 'make'.
'whole-size-limit'
'-l' in 'shar'.
'width'
'-w' in 'ls' and 'ptx'.
'word-regexp'
'-W' in 'ptx'.
'writable'
'-T' in 'who'.
'zeros'
'-z' in 'gprof'.
File: standards.info, Node: OID Allocations, Next: Memory Usage, Prev: Option Table, Up: Program Behavior
4.10 OID Allocations
====================
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
<http://www.alvestrand.no/objectid>; has a (voluntary) listing of many
OID assignments.
If you need a new slot for your GNU package, write
<maintainers AT gnu.org>. Here is a list of arcs currently assigned:
1.3.6.1.4.1.11591 GNU
1.3.6.1.4.1.11591.1 GNU Radius
1.3.6.1.4.1.11591.2 GnuPG
1.3.6.1.4.1.11591.2.1 notation
1.3.6.1.4.1.11591.2.1.1 pkaAddress
1.3.6.1.4.1.11591.3 GNU Radar
1.3.6.1.4.1.11591.4 GNU GSS
1.3.6.1.4.1.11591.5 GNU Mailutils
1.3.6.1.4.1.11591.6 GNU Shishi
1.3.6.1.4.1.11591.7 GNU Radio
1.3.6.1.4.1.11591.8 GNU Dico
1.3.6.1.4.1.11591.9 GNU Rush
1.3.6.1.4.1.11591.12 digestAlgorithm
1.3.6.1.4.1.11591.12.2 TIGER/192
1.3.6.1.4.1.11591.13 encryptionAlgorithm
1.3.6.1.4.1.11591.13.2 Serpent
1.3.6.1.4.1.11591.13.2.1 Serpent-128-ECB
1.3.6.1.4.1.11591.13.2.2 Serpent-128-CBC
1.3.6.1.4.1.11591.13.2.3 Serpent-128-OFB
1.3.6.1.4.1.11591.13.2.4 Serpent-128-CFB
1.3.6.1.4.1.11591.13.2.21 Serpent-192-ECB
1.3.6.1.4.1.11591.13.2.22 Serpent-192-CBC
1.3.6.1.4.1.11591.13.2.23 Serpent-192-OFB
1.3.6.1.4.1.11591.13.2.24 Serpent-192-CFB
1.3.6.1.4.1.11591.13.2.41 Serpent-256-ECB
1.3.6.1.4.1.11591.13.2.42 Serpent-256-CBC
1.3.6.1.4.1.11591.13.2.43 Serpent-256-OFB
1.3.6.1.4.1.11591.13.2.44 Serpent-256-CFB
1.3.6.1.4.1.11591.14 CRC algorithms
1.3.6.1.4.1.11591.14.1 CRC 32
1.3.6.1.4.1.11591.15 ellipticCurve
1.3.6.1.4.1.11591.15.1 Ed25519
File: standards.info, Node: Memory Usage, Next: File Usage, Prev: OID Allocations, Up: Program Behavior
4.11 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 memory to operate
on them.
However, for programs such as 'cat' or 'tail', that can usefully
operate on very large files, it is important to avoid using a technique
that would artificially limit the size of files it can handle. 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 memory all at once.
If your program creates complicated data structures, just make them
in memory and give a fatal error if 'malloc' returns 'NULL'.
Memory analysis tools such as '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.
File: standards.info, Node: File Usage, Prev: Memory Usage, Up: Program Behavior
4.12 File Usage
===============
Programs should be prepared to operate when '/usr' and '/etc' are
read-only file systems. Thus, if the program manages log files, lock
files, backup files, score files, or any other files which are modified
for internal purposes, these files should not be stored in '/usr' or
'/etc'.
There are two exceptions. '/etc' is used to store system
configuration information; it is reasonable for a program to modify
files in '/etc' when its job is to update the system configuration.
Also, if the user explicitly asks to modify one file in a directory, it
is reasonable for the program to store other files in the same
directory.
File: standards.info, Node: Writing C, Next: Documentation, Prev: Program Behavior, Up: Top
5 Making The Best Use of C
**************************
This chapter provides advice on how best to use the C language 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 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 "..." or '...' in the C locale.
* Mmap:: How you can safely use 'mmap'.
File: standards.info, Node: Formatting, Next: Comments, Up: Writing C
5.1 Formatting Your Source Code
===============================
Please keep the length of source lines to 79 characters or less, for
maximum readability in the widest range of environments.
It is important to put the open-brace that starts the body of a C
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 '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
definitions, and may also help certain tools recognize them. Thus,
using Standard C syntax, the format is this:
static char *
concat (char *s1, char *s2)
{
...
}
or, if you want to use traditional C syntax, format the definition like
this:
static char *
concat (s1, s2) /* Name starts in column one here */
char *s1, *s2;
{ /* Open brace in column one here */
...
}
In Standard C, if the arguments don't fit nicely on one line, split
it like this:
int
lots_of_args (int an_integer, long a_long, short a_short,
double a_double, float a_float)
...
For 'struct' and 'enum' types, likewise put the braces in column one,
unless the whole contents fits on one line:
struct foo
{
int a, b;
}
or
struct foo { int a, b; }
The rest of this section gives our recommendations for other aspects
of C formatting style, which is also the default style of the 'indent'
program in version 1.2 and newer. It corresponds to the options
-nbad -bap -nbc -bbo -bl -bli2 -bls -ncdb -nce -cp1 -cs -di2
-ndj -nfc1 -nfca -hnl -i2 -ip5 -lp -pcs -psl -nsc -nsob
We don't think of these recommendations as requirements, because it
causes no problems for users if two different programs have different
formatting styles.
But whatever style you use, please use it consistently, since a
mixture of styles within one program tends to look ugly. If you are
contributing changes to an existing program, please follow the style of
that program.
For the body of the function, our recommended style looks like this:
if (x < foo (y, z))
haha = bar[4] + 5;
else
{
while (z)
{
haha += foo (z, z);
z--;
}
return ++x + bar ();
}
We find it easier to read a program when it has spaces before the
open-parentheses and after the commas. Especially after the commas.
When you split an expression into multiple lines, split it before an
operator, not after one. Here is the right way:
if (foo_this_is_long && bar > win (x, y, z)
&& remaining_condition)
Try to avoid having two operators of different precedence at the same
level of indentation. For example, don't write this:
mode = (inmode[j] == VOIDmode
|| GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])
? outmode[j] : inmode[j]);
Instead, use extra parentheses so that the indentation shows the
nesting:
mode = ((inmode[j] == VOIDmode
|| (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])))
? outmode[j] : inmode[j]);
Insert extra parentheses so that Emacs will indent the code properly.
For example, the following indentation looks nice if you do it by hand,
v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
+ rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000;
but Emacs would alter it. Adding a set of parentheses produces
something that looks equally nice, and which Emacs will preserve:
v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
+ rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000);
Format do-while statements like this:
do
{
a = foo (a);
}
while (a > 0);
Please use formfeed characters (control-L) to divide the program into
pages at logical places (but not within a function). It does not matter
just how long the pages are, since they do not have to fit on a printed
page. The formfeeds should appear alone on lines by themselves.
File: standards.info, Node: Comments, Next: Syntactic Conventions, Prev: Formatting, Up: Writing C
5.2 Commenting Your Work
========================
Every program should start with a comment saying briefly what it is for.
Example: 'fmt - filter for simple filling of text'. This comment should
be at the top of the source file containing the 'main' function of the
program.
Also, please write a brief comment at the start of each source file,
with the file name and a line or two about the overall purpose of the
file.
Please write the comments in a GNU program in English, because
English is the one language that nearly all programmers in all countries
can read. If you do not write English well, please write comments in
English as well as you can, then ask other people to help rewrite them.
If you can't write comments in English, please find someone to work with
you and translate your comments into English.
Please put a comment on each function saying what the function does,
what sorts of arguments it gets, and what the possible values of
arguments mean and are used for. It is not necessary to duplicate in
words the meaning of the C argument declarations, if a C type is being
used in its customary fashion. If there is anything nonstandard about
its use (such as an argument of type 'char *' which is really the
address of the second character of a string, not the first), or any
possible values that would not work the way one would expect (such as,
that strings containing newlines are not guaranteed to work), be sure to
say so.
Also explain the significance of the return value, if there is one.
Please put two spaces after the end of a sentence in your comments,
so that the Emacs sentence commands will work. Also, please write
complete sentences and capitalize the first word. If a lower-case
identifier comes at the beginning of a sentence, don't capitalize it!
Changing the spelling makes it a different identifier. If you don't
like starting a sentence with a lower case letter, write the sentence
differently (e.g., "The identifier lower-case is ...").
The comment on a function is much clearer if you use the argument
names to speak about the argument values. The variable name itself
should be lower case, but write it in upper case when you are speaking
about the value rather than the variable itself. Thus, "the inode
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 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.
There should be a comment on each static variable as well, like this:
/* Nonzero means truncate lines in the display;
zero means continue them. */
int truncate_lines;
Every '#endif' should have a comment, except in the case of short
conditionals (just a few lines) that are not nested. The comment should
state the condition of the conditional that is ending, _including its
sense_. '#else' should have a comment describing the condition _and
sense_ of the code that follows. For example:
#ifdef foo
...
#else /* not foo */
...
#endif /* not foo */
#ifdef foo
...
#endif /* foo */
but, by contrast, write the comments this way for a '#ifndef':
#ifndef foo
...
#else /* foo */
...
#endif /* foo */
#ifndef foo
...
#endif /* not foo */
File: standards.info, Node: Syntactic Conventions, Next: Names, Prev: Comments, Up: Writing C
5.3 Clean Use of C Constructs
=============================
Please explicitly declare the types of all objects. For example, you
should explicitly declare all arguments to functions, and you should
declare functions to return 'int' rather than omitting the 'int'.
Some programmers like to use the GCC '-Wall' option, and change the
code whenever it issues a warning. If you want to do this, then do.
Other programmers prefer not to use '-Wall', because it gives warnings
for valid and legitimate code which they do not want to change. If you
want to do this, then do. The compiler should be your servant, not your
master.
Don't make the program ugly just to placate static analysis tools
such as 'lint', 'clang', and GCC with extra warnings options such as
'-Wconversion' and '-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 '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 should go in a header file. Don't put 'extern' declarations inside
functions.
It used to be common practice to use the same local variables (with
names like 'tem') over and over for different values within one
function. Instead of doing this, it is better to declare a separate
local variable for each distinct purpose, and give it a name which is
meaningful. This not only makes programs easier to understand, it also
facilitates optimization by good compilers. You can also move the
declaration of each local variable into the smallest scope that includes
all its uses. This makes the program even cleaner.
Don't use local variables or parameters that shadow global
identifiers. GCC's '-Wshadow' option can detect this problem.
Don't declare multiple variables in one declaration that spans lines.
Start a new declaration on each line, instead. For example, instead of
this:
int foo,
bar;
write either this:
int foo, bar;
or this:
int foo;
int bar;
(If they are global variables, each should have a comment preceding it
anyway.)
When you have an 'if'-'else' statement nested in another 'if'
statement, always put braces around the 'if'-'else'. Thus, never write
like this:
if (foo)
if (bar)
win ();
else
lose ();
always like this:
if (foo)
{
if (bar)
win ();
else
lose ();
}
If you have an 'if' statement nested inside of an 'else' statement,
either write 'else if' on one line, like this,
if (foo)
...
else if (bar)
...
with its 'then'-part indented like the preceding 'then'-part, or write
the nested 'if' within braces like this:
if (foo)
...
else
{
if (bar)
...
}
Don't declare both a structure tag and variables or typedefs in the
same declaration. Instead, declare the structure tag separately and
then use it to declare the variables or typedefs.
Try to avoid assignments inside 'if'-conditions (assignments inside
'while'-conditions are ok). For example, don't write this:
if ((foo = (char *) malloc (sizeof *foo)) == NULL)
fatal ("virtual memory exhausted");
instead, write this:
foo = (char *) malloc (sizeof *foo);
if (foo == NULL)
fatal ("virtual memory exhausted");
File: standards.info, Node: Names, Next: System Portability, Prev: Syntactic Conventions, Up: Writing C
5.4 Naming Variables, Functions, and Files
==========================================
The names of global variables and functions in a program serve as
comments of a sort. So don't choose terse names--instead, look for
names that give useful information about the meaning of the variable or
function. In a GNU program, names should be English, like other
comments.
Local variable names can be shorter, because they are used only
within one context, where (presumably) comments explain their purpose.
Try to limit your use of abbreviations in symbol names. It is ok to
make a few abbreviations, explain what they mean, and then use them
frequently, but don't use lots of obscure abbreviations.
Please use underscores to separate words in a name, so that the Emacs
word commands can be useful within them. Stick to lower case; reserve
upper case for macros and 'enum' constants, and for name-prefixes that
follow a uniform convention.
For example, you should use names like 'ignore_space_change_flag';
don't use names like 'iCantReadThis'.
Variables that indicate whether command-line options have been
specified should be named after the meaning of the option, not after the
option-letter. A comment should state both the exact meaning of the
option and its letter. For example,
/* Ignore changes in horizontal whitespace (-b). */
int ignore_space_change_flag;
When you want to define names with constant integer values, use
'enum' rather than '#define'. GDB knows about enumeration constants.
You might want to make sure that none of the file names would
conflict if the files were loaded onto an MS-DOS file system which
shortens the names. You can use the program 'doschk' to test for this.
Some GNU programs were designed to limit themselves to file names of
14 characters or less, to avoid file name conflicts if they are read
into older System V systems. Please preserve this feature in the
existing GNU programs that have it, but there is no need to do this in
new GNU programs. 'doschk' also reports file names longer than 14
characters.
File: standards.info, Node: System Portability, Next: CPU Portability, Prev: Names, Up: Writing C
5.5 Portability between System Types
====================================
In the Unix world, "portability" refers to porting to different Unix
versions. For a GNU program, this kind of portability is desirable, but
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 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.
Beyond that, it is good to support the other free operating systems
(*BSD), and it is nice to support other Unix-like systems if you want
to. Supporting a variety of Unix-like systems is desirable, although
not paramount. It is usually not too hard, so you may as well do it.
But you don't have to consider it an obligation, if it does turn out to
be hard.
The easiest way to achieve portability to most Unix-like systems is
to use Autoconf. It's unlikely that your program needs to know more
information about the host platform than Autoconf can provide, simply
because most of the programs that need such knowledge have already been
written.
Avoid using the format of semi-internal data bases (e.g.,
directories) when there is a higher-level alternative ('readdir').
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 that will be useful on GNU and GNU/Linux, rather than on
supporting other incompatible systems.
If you do support Windows, please do not abbreviate it as "win". In
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 "win", you can write it in full or abbreviate it to "woe" or "w". In
GNU Emacs, for instance, we use 'w32' in file names of Windows-specific
files, but the macro for Windows conditionals is called 'WINDOWSNT'.
It is a good idea to define the "feature test macro" '_GNU_SOURCE'
when compiling your C files. When you compile on GNU or GNU/Linux, this
will enable the declarations of GNU library extension functions, and
that will usually give you a compiler error message if you define the
same function names in some other way in your program. (You don't have
to actually _use_ these functions, if you prefer to make the program
more portable to other systems.)
But whether or not you use these GNU extensions, you should avoid
using their names for any other meanings. Doing so would make it hard
to move your code into other GNU programs.
File: standards.info, Node: CPU Portability, Next: System Functions, Prev: System Portability, Up: Writing C
5.6 Portability between CPUs
============================
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 'int' will be less than
32 bits. We don't support 16-bit machines in GNU.
Similarly, don't make any effort to cater to the possibility that
'long' will be smaller than predefined types like 'size_t'. For
example, the following code is ok:
printf ("size = %lu\n", (unsigned long) sizeof array);
printf ("diff = %ld\n", (long) (pointer2 - pointer1));
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.
Predefined file-size types like 'off_t' are an exception: they are
longer than 'long' on many platforms, so code like the above won't work
with them. One way to print an 'off_t' value portably is to print its
digits yourself, one by one.
Don't assume that the address of an 'int' object is also the address
of its least-significant byte. This is false on big-endian machines.
Thus, don't make the following mistake:
int c;
...
while ((c = getchar ()) != EOF)
write (file_descriptor, &c, 1);
Instead, use 'unsigned char' as follows. (The 'unsigned' is for
portability to unusual systems where 'char' is signed and where there is
integer overflow checking.)
int c;
while ((c = getchar ()) != EOF)
{
unsigned char u = c;
write (file_descriptor, &u, 1);
}
Avoid casting pointers to integers if you can. Such casts greatly
reduce portability, and in most programs they are easy to avoid. In the
cases where casting pointers to integers is essential--such as, a Lisp
interpreter which stores type information as well as an address in one
word--you'll have to make explicit provisions to handle different word
sizes. You will also need to make provision for systems in which the
normal range of addresses you can get from 'malloc' starts far away from
zero.
File: standards.info, Node: System Functions, Next: Internationalization, Prev: CPU Portability, Up: Writing C
5.7 Calling System Functions
============================
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.
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:
'open'
Names with trailing '/''s are mishandled on many platforms.
'printf'
'long double' may be unimplemented; floating values Infinity and
NaN are often mishandled; output for large precisions may be
incorrect.
'readlink'
May return 'int' instead of 'ssize_t'.
'scanf'
On Windows, 'errno' is not set on failure.
Gnulib (http://www.gnu.org/software/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.
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 ('xmalloc', '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: *note Introduction: (gnulib)Top. and *note
(autoconf)Portable C and C++::. Please consult them for many more
details.
File: standards.info, Node: Internationalization, Next: Character Set, Prev: System Functions, Up: Writing C
5.8 Internationalization
========================
GNU has a library called GNU gettext that makes it easy to translate the
messages in a program into various languages. You should use this
library in every program. Use English for the messages as they appear
in the program, and let gettext provide the way to translate them into
other languages.
Using GNU gettext involves putting a call to the 'gettext' macro
around each string that might need translation--like this:
printf (gettext ("Processing file '%s'..."), file);
This permits GNU gettext to replace the string '"Processing file
'%s'..."' with a translated version.
Once a program uses gettext, please make a point of writing calls to
'gettext' when you add new strings that call for translation.
Using GNU gettext in a package involves specifying a "text domain
name" for the package. The text domain name is used to separate the
translations for this package from the translations for other packages.
Normally, the text domain name should be the same as the name of the
package--for example, 'coreutils' for the GNU core utilities.
To enable gettext to work well, avoid writing code that makes
assumptions about the structure of words or sentences. When you want
the precise text of a sentence to vary depending on the data, use two or
more alternative string constants each containing a complete sentences,
rather than inserting conditionalized words or phrases into a single
sentence framework.
Here is an example of what not to do:
printf ("%s is full", capacity > 5000000 ? "disk" : "floppy disk");
If you apply gettext to all strings, like this,
printf (gettext ("%s is full"),
capacity > 5000000 ? gettext ("disk") : gettext ("floppy disk"));
the translator will hardly know that "disk" and "floppy disk" are meant
to be substituted in the other string. Worse, in some languages (like
French) the construction will not work: the translation of the word
"full" depends on the gender of the first part of the sentence; it
happens to be not the same for "disk" as for "floppy disk".
Complete sentences can be translated without problems:
printf (capacity > 5000000 ? gettext ("disk is full")
: gettext ("floppy disk is full"));
A similar problem appears at the level of sentence structure with
this code:
printf ("# Implicit rule search has%s been done.\n",
f->tried_implicit ? "" : " not");
Adding '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 'gettext'
calls does the job straightforwardly if the code starts out like this:
printf (f->tried_implicit
? "# Implicit rule search has been done.\n",
: "# Implicit rule search has not been done.\n");
Another example is this one:
printf ("%d file%s processed", nfiles,
nfiles != 1 ? "s" : "");
The problem with this example is that it assumes that plurals are made
by adding 's'. If you apply gettext to the format string, like this,
printf (gettext ("%d file%s processed"), nfiles,
nfiles != 1 ? "s" : "");
the message can use different words, but it will still be forced to use
's' for the plural. Here is a better way, with gettext being applied to
the two strings independently:
printf ((nfiles != 1 ? gettext ("%d files processed")
: gettext ("%d file processed")),
nfiles);
But this still doesn't work for languages like Polish, which has three
plural forms: one for nfiles == 1, one for nfiles == 2, 3, 4, 22, 23,
24, ... and one for the rest. The GNU 'ngettext' function solves this
problem:
printf (ngettext ("%d files processed", "%d file processed", nfiles),
nfiles);
File: standards.info, Node: Character Set, Next: Quote Characters, Prev: Internationalization, Up: Writing C
5.9 Character Set
=================
Sticking to the ASCII character set (plain text, 7-bit characters) is
preferred in GNU source code comments, text documents, and other
contexts, unless there is good reason to do something else because of
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 "Flore'al". Also, it is OK (but
not required) to use non-ASCII characters to represent proper names of
contributors in change logs (*note Change Logs::).
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.
File: standards.info, Node: Quote Characters, Next: Mmap, Prev: Character Set, Up: Writing C
5.10 Quote Characters
=====================
In the C locale, the output of GNU programs should stick to plain ASCII
for quotation characters in messages to users: preferably 0x22 ('"') or
0x27 (''') for both opening and closing quotes. Although GNU programs
traditionally used 0x60 ('`') for opening and 0x27 (''') for closing
quotes, nowadays quotes '`like this'' are typically rendered
asymmetrically, so quoting '"like this"' or ''like this'' typically
looks better.
It is ok, but not required, for GNU programs to generate
locale-specific quotes in non-C locales. For example:
printf (gettext ("Processing file '%s'..."), file);
Here, a French translation might cause 'gettext' to return the string
'"Traitement de fichier < %s >..."', yielding quotes more appropriate
for a French locale.
Sometimes a program may need to use opening and closing quotes
directly. By convention, 'gettext' translates the string '"`"' to the
opening quote and the string '"'"' 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.
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 '--quoting-style' of GNU 'ls'.
File: standards.info, Node: Mmap, Prev: Quote Characters, Up: Writing C
5.11 Mmap
=========
If you use '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 'mmap' is to try it on the specific file for
which you want to use it--and if 'mmap' doesn't work, fall back on doing
the job in another way using 'read' and 'write'.
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 'mmap', but
some do not. It is important to make programs handle all these kinds of
files.
File: standards.info, Node: Documentation, Next: Managing Releases, Prev: Writing C, Up: Top
6 Documenting Programs
**********************
A GNU program should ideally come with full free documentation, adequate
for both reference and tutorial purposes. If the package can be
programmed or extended, the documentation should cover programming or
extending it, as well as just using it.
* Menu:
* GNU Manuals:: Writing proper manuals.
* Doc Strings and Manuals:: Compiling doc strings doesn't make a manual.
* Manual Structure Details:: Specific structure conventions.
* License for Manuals:: Writing the distribution terms for a manual.
* Manual Credits:: Giving credit to documentation contributors.
* Printed Manuals:: Mentioning the printed manual.
* NEWS File:: NEWS files supplement manuals.
* Change Logs:: Recording changes.
* Man Pages:: Man pages are secondary.
* Reading other Manuals:: How far you can go in learning
from other manuals.
File: standards.info, Node: GNU Manuals, Next: Doc Strings and Manuals, Up: Documentation
6.1 GNU Manuals
===============
The preferred document format for the GNU system is the Texinfo
formatting language. Every GNU package should (ideally) have
documentation in Texinfo both for reference and for learners. Texinfo
makes it possible to produce a good quality formatted book, using TeX,
and to generate an Info file. It is also possible to generate HTML
output from Texinfo source. See the Texinfo manual, either the
hardcopy, or the on-line version available through 'info' or the Emacs
Info subsystem ('C-h i').
Nowadays some other formats such as Docbook and Sgmltexi can be
converted automatically into Texinfo. It is ok to produce the Texinfo
documentation by conversion this way, as long as it gives good results.
Make sure your manual is clear to a reader who knows nothing about
the topic and reads it straight through. This means covering basic
topics at the beginning, and advanced topics only later. This also
means defining every specialized term when it is first used.
Programmers tend to carry over the structure of the program as the
structure for its documentation. But this structure is not necessarily
good for explaining how to use the program; it may be irrelevant and
confusing for a user.
Instead, the right way to structure documentation is according to the
concepts and questions that a user will have in mind when reading it.
This principle applies at every level, from the lowest (ordering
sentences in a paragraph) to the highest (ordering of chapter topics
within the manual). Sometimes this structure of ideas matches the
structure of the implementation of the software being documented--but
often they are different. An important part of learning to write good
documentation is to learn to notice when you have unthinkingly
structured the documentation like the implementation, stop yourself, and
look for better alternatives.
For example, each program in the GNU system probably ought to be
documented in one manual; but this does not mean each program should
have its own manual. That would be following the structure of the
implementation, rather than the structure that helps the user
understand.
Instead, each manual should cover a coherent _topic_. For example,
instead of a manual for 'diff' and a manual for 'diff3', we have one
manual for "comparison of files" which covers both of those programs, as
well as 'cmp'. By documenting these programs together, we can make the
whole subject clearer.
The manual which discusses a program should certainly document all of
the program's command-line options and all of its commands. It should
give examples of their use. But don't organize the manual as a list of
features. Instead, organize it logically, by subtopics. Address the
questions that a user will ask when thinking about the job that the
program does. Don't just tell the reader what each feature can do--say
what jobs it is good for, and show how to use it for those jobs.
Explain what is recommended usage, and what kinds of usage users should
avoid.
In general, a GNU manual should serve both as tutorial and reference.
It should be set up for convenient access to each topic through Info,
and for reading straight through (appendixes aside). A GNU manual
should give a good introduction to a beginner reading through from the
start, and should also provide all the details that hackers want. The
Bison manual is a good example of this--please take a look at it to see
what we mean.
That is not as hard as it first sounds. Arrange each chapter as a
logical breakdown of its topic, but order the sections, and write their
text, so that reading the chapter straight through makes sense. Do
likewise when structuring the book into chapters, and when structuring a
section into paragraphs. The watchword is, _at each point, address the
most fundamental and important issue raised by the preceding text._
If necessary, add extra chapters at the beginning of the manual which
are purely tutorial and cover the basics of the subject. These provide
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 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
*note Making Index Entries: (texinfo)Index Entries, and see *note
Defining the Entries of an Index: (texinfo)Indexing Commands.
Don't use Unix man pages as a model for how to write GNU
documentation; most of them are terse, badly structured, and give
inadequate explanation of the underlying concepts. (There are, of
course, some exceptions.) Also, Unix man pages use a particular format
which is different from what we use in GNU manuals.
Please include an email address in the manual for where to report
bugs _in the text of the manual_.
Please do not use the term "pathname" that is used in Unix
documentation; use "file name" (two words) instead. We use the term
"path" only for search paths, which are lists of directory names.
Please do not use the term "illegal" to refer to erroneous input to a
computer program. Please use "invalid" for this, and reserve the term
"illegal" for activities prohibited by law.
Please do not write '()' after a function name just to indicate it is
a function. 'foo ()' is not a function, it is a function call with no
arguments.
Whenever possible, please stick to the active voice, avoiding the
passive, and use the present tense, not the future teste. For instance,
write "The function 'foo' returns a list containing A and B" rather than
"A list containing A and B will be returned." One advantage of the
active voice is it requires you to state the subject of the sentence;
with the passive voice, you might omit the subject, which leads to
vagueness.
It is proper to use the future tense when grammar demands it, as in,
"If you type 'x', the computer will self-destruct in 10 seconds."
File: standards.info, Node: Doc Strings and Manuals, Next: Manual Structure Details, Prev: GNU Manuals, Up: Documentation
6.2 Doc Strings and Manuals
===========================
Some programming systems, such as Emacs, provide a documentation string
for each function, command or variable. You may be tempted to write a
reference manual by compiling the documentation strings and writing a
little additional text to go around them--but you must not do it. That
approach is a fundamental mistake. The text of well-written
documentation strings will be entirely wrong for a manual.
A documentation string needs to stand alone--when it appears on the
screen, there will be no other text to introduce or explain it.
Meanwhile, it can be rather informal in style.
The text describing a function or variable in a manual must not stand
alone; it appears in the context of a section or subsection. Other text
at the beginning of the section should explain some of the concepts, and
should often make some general points that apply to several functions or
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
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 is to use them as a source of information for writing good text.
File: standards.info, Node: Manual Structure Details, Next: License for Manuals, Prev: Doc Strings and Manuals, Up: Documentation
6.3 Manual Structure Details
============================
The title page of the manual should state the version of the programs or
packages documented in the manual. The Top node of the manual should
also contain this information. If the manual is changing more
frequently than or independent of the program, also state a version
number for the manual in both of these places.
Each program documented in the manual should have a node named
'PROGRAM Invocation' or 'Invoking PROGRAM'. This node (together with
its subnodes, if any) should describe the program's command line
arguments and how to run it (the sort of information people would look
for in a man page). Start with an '@example' containing a template for
all the options and arguments that the program uses.
Alternatively, put a menu item in some menu whose item name fits one
of the above patterns. This identifies the node which that item points
to as the node for this purpose, regardless of the node's actual name.
The '--usage' feature of the Info reader looks for such a node or
menu item in order to find the relevant text, so it is essential for
every Texinfo file to have one.
If one manual describes several programs, it should have such a node
for each program described in the manual.
File: standards.info, Node: License for Manuals, Next: Manual Credits, Prev: Manual Structure Details, Up: Documentation
6.4 License for Manuals
=======================
Please use the GNU Free Documentation License for all GNU manuals that
are more than a few pages long. Likewise for a collection of short
documents--you only need one copy of the GNU FDL for the whole
collection. For a single short document, you can use a very permissive
non-copyleft license, to avoid taking up space with a long license.
See <http://www.gnu.org/copyleft/fdl-howto.html>; for more explanation
of how to employ the GFDL.
Note that it is not obligatory to include a copy of the GNU GPL or
GNU LGPL in a manual whose license is neither the GPL nor the LGPL. It
can be a good idea to include the program's license in a large manual;
in a short manual, whose size would be increased considerably by
including the program's license, it is probably better not to include
it.
File: standards.info, Node: Manual Credits, Next: Printed Manuals, Prev: License for Manuals, Up: Documentation
6.5 Manual Credits
==================
Please credit the principal human writers of the manual as the authors,
on the title page of the manual. If a company sponsored the work, thank
the company in a suitable place in the manual, but do not cite the
company as an author.
File: standards.info, Node: Printed Manuals, Next: NEWS File, Prev: Manual Credits, Up: Documentation
6.6 Printed Manuals
===================
The FSF publishes some GNU manuals in printed form. To encourage sales
of these manuals, the on-line versions of the manual should mention at
the very start that the printed manual is available and should point at
information for getting it--for instance, with a link to the page
<http://www.gnu.org/order/order.html>;. This should not be included in
the printed manual, though, because there it is redundant.
It is also useful to explain in the on-line forms of the manual how
the user can print out the manual from the sources.
File: standards.info, Node: NEWS File, Next: Change Logs, Prev: Printed Manuals, Up: Documentation
6.7 The NEWS File
=================
In addition to its manual, the package should have a file named 'NEWS'
which contains a list of user-visible changes worth mentioning. In each
new release, add items to the front of the file and identify the version
they pertain to. Don't discard old items; leave them in the file after
the newer items. This way, a user upgrading from any previous version
can see what is new.
If the 'NEWS' file gets very long, move some of the older items into
a file named 'ONEWS' and put a note at the end referring the user to
that file.
File: standards.info, Node: Change Logs, Next: Man Pages, Prev: NEWS File, Up: Documentation
6.8 Change Logs
===============
Keep a change log to describe all the changes made to program source
files. The purpose of this is so that people investigating bugs in the
future will know about the changes that might have introduced the bug.
Often a new bug can be found by looking at what was recently changed.
More importantly, change logs can help you eliminate conceptual
inconsistencies between different parts of a program, by giving you a
history of how the conflicting concepts arose and who they came from.
* Menu:
* Change Log Concepts::
* Style of Change Logs::
* Simple Changes::
* Conditional Changes::
* Indicating the Part Changed::
File: standards.info, Node: Change Log Concepts, Next: Style of Change Logs, Up: Change Logs
6.8.1 Change Log Concepts
-------------------------
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. Each "entry" in a
change log describes either an individual change or the smallest batch
of changes that belong together, also known as a "change set". For
later reference or for summarizing, sometimes it is useful to start the
entry with a one-line description (sometimes called a "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 '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
you.
Another alternative is to record change log information with a
version control system such as RCS or CVS. This can be converted
automatically to a 'ChangeLog' file using 'rcs2log'; in Emacs, the
command 'C-x v a' ('vc-update-change-log') does the job.
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, how
to call it, and so on.
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 'ChangeLog' is with the Emacs
command '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.
File: standards.info, Node: Style of Change Logs, Next: Simple Changes, Prev: Change Log Concepts, Up: Change Logs
6.8.2 Style of Change Logs
--------------------------
Here are some simple examples of change log entries, starting with the
header line that says who made the change and when it was installed,
followed by descriptions of specific changes. (These examples are drawn
from Emacs and GCC.)
1998-08-17 Richard Stallman <rms AT gnu.org>
* register.el (insert-register): Return nil.
(jump-to-register): Likewise.
* sort.el (sort-subr): Return nil.
* tex-mode.el (tex-bibtex-file, tex-file, tex-region):
Restart the tex shell if process is gone or stopped.
(tex-shell-running): New function.
* expr.c (store_one_arg): Round size up for move_block_to_reg.
(expand_call): Round up when emitting USE insns.
* stmt.c (assign_parms): Round size up for move_block_from_reg.
It's important to name the changed function or variable in full.
Don't abbreviate function or variable names, and don't combine them.
Subsequent maintainers will often search for a function name to find all
the change log entries that pertain to it; if you abbreviate the name,
they won't find it when they search.
For example, some people are tempted to abbreviate groups of function
names by writing '* register.el ({insert,jump-to}-register)'; this is
not a good idea, since searching for 'jump-to-register' or
'insert-register' would not find that entry.
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
')', rather than ',', and opening the continuation with '(' as in this
example:
* keyboard.c (menu_bar_items, tool_bar_items)
(Fexecute_extended_command): Deal with 'keymap' property.
When you install someone else's changes, put the contributor's name
in the change log entry rather than in the text of the entry. In other
words, write this:
2002-07-14 John Doe <jdoe AT gnu.org>
* sewing.c: Make it sew.
rather than this:
2002-07-14 Usual Maintainer <usual AT gnu.org>
* sewing.c: Make it sew. Patch by jdoe AT gnu.org.
As for the date, that should be the date you applied the change.
File: standards.info, Node: Simple Changes, Next: Conditional Changes, Prev: Style of Change Logs, Up: Change Logs
6.8.3 Simple Changes
--------------------
Certain simple kinds of changes don't need much detail in the change
log.
When you change the calling sequence of a function in a simple
fashion, and you change all the callers of the function to use the new
calling sequence, there is no need to make individual entries for all
the callers that you changed. Just write in the entry for the function
being called, "All callers changed"--like this:
* keyboard.c (Fcommand_execute): New arg SPECIAL.
All callers changed.
When you change just comments or doc strings, it is enough to write
an entry for the file, without mentioning the functions. Just "Doc
fixes" is enough for the change log.
There's no technical need to make change log entries for
documentation files. This is because documentation is not susceptible
to bugs that are hard to fix. Documentation does not consist of parts
that must interact in a precisely engineered fashion. To correct an
error, you need not know the history of the erroneous passage; it is
enough to compare what the documentation says with the way the program
actually works.
However, you should keep change logs for documentation files when the
project gets copyright assignments from its contributors, so as to make
the records of authorship more accurate.
File: standards.info, Node: Conditional Changes, Next: Indicating the Part Changed, Prev: Simple Changes, Up: Change Logs
6.8.4 Conditional Changes
-------------------------
Source files can often contain code that is conditional to build-time or
static conditions. For example, C programs can contain compile-time
'#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 'Makefile.am'
files can contain variable definitions or target declarations that are
only to be considered if a configure-time Automake conditional is true.
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.
Our convention for indicating conditional changes is to use _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:
* 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.
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 'FRAME_WINDOW_P' is defined (and used) only
when the macro 'HAVE_X_WINDOWS' is defined:
* frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined.
Next, an entry for a change within the function 'init_display', whose
definition as a whole is unconditional, but the changes themselves are
contained in a '#ifdef HAVE_LIBNCURSES' conditional:
* dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent.
Finally, here is an entry for a change that takes effect only when a
certain macro is _not_ defined:
* host.c (gethostname) [!HAVE_SOCKETS]: Replace with winsock version.
File: standards.info, Node: Indicating the Part Changed, Prev: Conditional Changes, Up: Change Logs
6.8.5 Indicating the Part Changed
---------------------------------
Indicate the part of a function which changed by using angle brackets
enclosing an indication of what the changed part does. Here is an entry
for a change in the part of the function 'sh-while-getopts' that deals
with 'sh' commands:
* progmodes/sh-script.el (sh-while-getopts) <sh>: Handle case that
user-specified option string is empty.
File: standards.info, Node: Man Pages, Next: Reading other Manuals, Prev: Change Logs, Up: Documentation
6.9 Man Pages
=============
In the GNU project, man pages are secondary. It is not necessary or
expected for every GNU program to have a man page, but some of them do.
It's your choice whether to include a man page in your program.
When you make this decision, consider that supporting a man page
requires continual effort each time the program is changed. The time
you spend on the man page is time taken away from more useful work.
For a simple program which changes little, updating the man page may
be a small job. Then there is little reason not to include a man page,
if you have one.
For a large program that changes a great deal, updating a man page
may be a substantial burden. If a user offers to donate a man page, you
may find this gift costly to accept. It may be better to refuse the man
page unless the same person agrees to take full responsibility for
maintaining it--so that you can wash your hands of it entirely. If this
volunteer later ceases to do the job, then don't feel obliged to pick it
up yourself; it may be better to withdraw the man page from the
distribution until someone else agrees to update it.
When a program changes only a little, you may feel that the
discrepancies are small enough that the man page remains useful without
updating. If so, put a prominent note near the beginning of the man
page explaining that you don't maintain it and that the Texinfo manual
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 (*note (maintain)License Notices for Other Files::).
For long man pages, with enough explanation and documentation that
they can be considered true manuals, use the GFDL (*note License for
Manuals::).
Finally, the GNU help2man program
(<http://www.gnu.org/software/help2man/>;) is one way to automate
generation of a man page, in this case from '--help' output. This is
sufficient in many cases.
File: standards.info, Node: Reading other Manuals, Prev: Man Pages, Up: Documentation
6.10 Reading other Manuals
==========================
There may be non-free books or documentation files that describe the
program you are documenting.
It is ok to use these documents for reference, just as the author of
a new algebra textbook can read other books on algebra. A large portion
of any non-fiction book consists of facts, in this case facts about how
a certain program works, and these facts are necessarily the same for
everyone who writes about the subject. But be careful not to copy your
outline structure, wording, tables or examples from preexisting non-free
documentation. Copying from free documentation may be ok; please check
with the FSF about the individual case.
File: standards.info, Node: Managing Releases, Next: References, Prev: Documentation, Up: Top
7 The Release Process
*********************
Making a release is more than just bundling up your source files in a
tar file and putting it up for FTP. You should set up your software so
that it can be configured to run on a variety of systems. Your Makefile
should conform to the GNU standards described below, and your directory
layout should also conform to the standards discussed below. Doing so
makes it easy to include your package into the larger framework of all
GNU software.
* Menu:
* Configuration:: How configuration of GNU packages should work.
* Makefile Conventions:: Makefile conventions.
* Releases:: Making releases
File: standards.info, Node: Configuration, Next: Makefile Conventions, Up: Managing Releases
7.1 How Configuration Should Work
=================================
Each GNU distribution should come with a shell script named 'configure'.
This script is given arguments which describe the kind of machine and
system you want to compile the program for. The 'configure' script must
record the configuration options so that they affect compilation.
The description here is the specification of the interface for the
'configure' script in GNU packages. Many packages implement it using
GNU Autoconf (*note Introduction: (autoconf)Top.) and/or GNU Automake
(*note Introduction: (automake)Top.), but you do not have to use these
tools. You can implement it any way you like; for instance, by making
'configure' be a wrapper around a completely different configuration
system.
Another way for the 'configure' script to operate is to make a link
from a standard name such as 'config.h' to the proper configuration file
for the chosen system. If you use this technique, the distribution
should _not_ contain a file named 'config.h'. This is so that people
won't be able to build the program without configuring it first.
Another thing that 'configure' can do is to edit the Makefile. If
you do this, the distribution should _not_ contain a file named
'Makefile'. Instead, it should include a file 'Makefile.in' which
contains the input used for editing. Once again, this is so that people
won't be able to build the program without configuring it first.
If 'configure' does write the 'Makefile', then 'Makefile' should have
a target named 'Makefile' which causes 'configure' to be rerun, setting
up the same configuration that was set up last time. The files that
'configure' reads should be listed as dependencies of 'Makefile'.
All the files which are output from the 'configure' script should
have comments at the beginning explaining that they were generated
automatically using 'configure'. This is so that users won't think of
trying to edit them by hand.
The 'configure' script should write a file named 'config.status'
which describes which configuration options were specified when the
program was last configured. This file should be a shell script which,
if run, will recreate the same configuration.
The 'configure' script should accept an option of the form
'--srcdir=DIRNAME' to specify the directory where sources are found (if
it is not the current directory). This makes it possible to build the
program in a separate directory, so that the actual source directory is
not modified.
If the user does not specify '--srcdir', then 'configure' should
check both '.' and '..' to see if it can find the sources. If it finds
the sources in one of these places, it should use them from there.
Otherwise, it should report that it cannot find the sources, and should
exit with nonzero status.
Usually the easy way to support '--srcdir' is by editing a definition
of 'VPATH' into the Makefile. Some rules may need to refer explicitly
to the specified source directory. To make this possible, 'configure'
can add to the Makefile a variable named 'srcdir' whose value is
precisely the specified directory.
In addition, the 'configure' script should take options corresponding
to most of the standard directory variables (*note Directory
Variables::). Here is the list:
--prefix --exec-prefix --bindir --sbindir --libexecdir --sysconfdir
--sharedstatedir --localstatedir --runstatedir
--libdir --includedir --oldincludedir
--datarootdir --datadir --infodir --localedir --mandir --docdir
--htmldir --dvidir --pdfdir --psdir
The 'configure' script should also take an argument which specifies
the type of system to build the program for. This argument should look
like this:
CPU-COMPANY-SYSTEM
For example, an Athlon-based GNU/Linux system might be
'i686-pc-linux-gnu'.
The 'configure' script needs to be able to decode all plausible
alternatives for how to describe a machine. Thus, 'athlon-pc-gnu/linux'
would be a valid alias. There is a shell script called 'config.sub'
(http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD)
that you can use as a subroutine to validate system types and
canonicalize aliases.
The 'configure' script should also take the option
'--build=BUILDTYPE', which should be equivalent to a plain BUILDTYPE
argument. For example, 'configure --build=i686-pc-linux-gnu' is
equivalent to 'configure i686-pc-linux-gnu'. When the build type is not
specified by an option or argument, the 'configure' script should
normally guess it using the shell script 'config.guess'
(http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD).
Other options are permitted to specify in more detail the software 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:
'--enable-FEATURE[=PARAMETER]'
Configure the package to build and install an optional user-level
facility called FEATURE. This allows users to choose which
optional features to include. Giving an optional PARAMETER of 'no'
should omit FEATURE, if it is built by default.
No '--enable' option should *ever* cause one feature to replace
another. No '--enable' option should ever substitute one useful
behavior for another useful behavior. The only proper use for
'--enable' is for questions of whether to build part of the program
or exclude it.
'--with-PACKAGE'
The package PACKAGE will be installed, so configure this package to
work with PACKAGE.
Possible values of PACKAGE include 'gnu-as' (or 'gas'), 'gnu-ld',
'gnu-libc', 'gdb', 'x', and 'x-toolkit'.
Do not use a '--with' option to specify the file name to use to
find certain files. That is outside the scope of what '--with'
options are for.
'VARIABLE=VALUE'
Set the value of the variable VARIABLE to VALUE. This is used to
override the default values of commands or arguments in the build
process. For example, the user could issue 'configure CFLAGS=-g
CXXFLAGS=-g' to build with debugging information and without the
default optimization.
Specifying variables as arguments to 'configure', like this:
./configure CC=gcc
is preferable to setting them in environment variables:
CC=gcc ./configure
as it helps to recreate the same configuration later with
'config.status'. However, both methods should be supported.
All '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 '--with-' or '--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 '--with-' and '--enable-' are
narrow: they *do not* provide a place for any sort of option you might
think of. That is deliberate. We want to limit the possible
configuration options in GNU software. We do not want GNU programs to
have idiosyncratic configuration options.
Packages that perform part of the compilation process may support
cross-compilation. In such a case, the host and target machines for the
program may be different.
The 'configure' script should normally treat the specified type of
system as both the host and the target, thus producing a program which
works for the same type of machine that it runs on.
To compile a program to run on a host type that differs from the
build type, use the configure option '--host=HOSTTYPE', where HOSTTYPE
uses the same syntax as BUILDTYPE. The host type normally defaults to
the build type.
To configure a cross-compiler, cross-assembler, or what have you, you
should specify a target different from the host, using the configure
option '--target=TARGETTYPE'. The syntax for TARGETTYPE is the same as
for the host type. So the command would look like this:
./configure --host=HOSTTYPE --target=TARGETTYPE
The target type normally defaults to the host type. Programs for
which cross-operation is not meaningful need not accept the '--target'
option, because configuring an entire operating system for
cross-operation is not a meaningful operation.
Some programs have ways of configuring themselves automatically. If
your program is set up to do this, your 'configure' script can simply
ignore most of its arguments.
File: standards.info, Node: Makefile Conventions, Next: Releases, Prev: Configuration, Up: Managing Releases
7.2 Makefile Conventions
========================
This node describes conventions for writing the Makefiles for GNU
programs. Using Automake will help you write a Makefile that follows
these conventions. For more information on portable Makefiles, see
POSIX and *note Portable Make Programming: (autoconf)Portable Make.
* Menu:
* Makefile Basics:: General conventions for Makefiles.
* Utilities in Makefiles:: Utilities to be used in Makefiles.
* Command Variables:: Variables for specifying commands.
* DESTDIR:: Supporting staged installs.
* Directory Variables:: Variables for installation directories.
* Standard Targets:: Standard targets for users.
* Install Command Categories:: Three categories of commands in the 'install'
rule: normal, pre-install and post-install.
File: standards.info, Node: Makefile Basics, Next: Utilities in Makefiles, Up: Makefile Conventions
7.2.1 General Conventions for Makefiles
---------------------------------------
Every Makefile should contain this line:
SHELL = /bin/sh
to avoid trouble on systems where the 'SHELL' variable might be
inherited from the environment. (This is never a problem with GNU
'make'.)
Different 'make' programs have incompatible suffix lists and implicit
rules, and this sometimes creates confusion or misbehavior. So it is a
good idea to set the suffix list explicitly using only the suffixes you
need in the particular Makefile, like this:
.SUFFIXES:
.SUFFIXES: .c .o
The first line clears out the suffix list, the second introduces all
suffixes which may be subject to implicit rules in this Makefile.
Don't assume that '.' is in the path for command execution. When you
need to run programs that are a part of your package during the make,
please make sure that it uses './' if the program is built as part of
the make or '$(srcdir)/' if the file is an unchanging part of the source
code. Without one of these prefixes, the current search path is used.
The distinction between './' (the "build directory") and '$(srcdir)/'
(the "source directory") is important because users can build in a
separate directory using the '--srcdir' option to 'configure'. A rule
of the form:
foo.1 : foo.man sedscript
sed -f sedscript foo.man > foo.1
will fail when the build directory is not the source directory, because
'foo.man' and 'sedscript' are in the source directory.
When using GNU 'make', relying on 'VPATH' to find the source file
will work in the case where there is a single dependency file, since the
'make' automatic variable '$<' will represent the source file wherever
it is. (Many versions of 'make' set '$<' only in implicit rules.) A
Makefile target like
foo.o : bar.c
$(CC) -I. -I$(srcdir) $(CFLAGS) -c bar.c -o foo.o
should instead be written as
foo.o : bar.c
$(CC) -I. -I$(srcdir) $(CFLAGS) -c $< -o $@
in order to allow 'VPATH' to work correctly. When the target has
multiple dependencies, using an explicit '$(srcdir)' is the easiest way
to make the rule work well. For example, the target above for 'foo.1'
is best written as:
foo.1 : foo.man sedscript
sed -f $(srcdir)/sedscript $(srcdir)/foo.man > $@
GNU distributions usually contain some files which are not source
files--for example, Info files, and the output from Autoconf, Automake,
Bison or Flex. Since these files normally appear in the source
directory, they should always appear in the source directory, not in the
build directory. So Makefile rules to update them should put the
updated files in the source directory.
However, if a file does not appear in the distribution, then the
Makefile should not put it in the source directory, because building a
program in ordinary circumstances should not modify the source directory
in any way.
Try to make the build and installation targets, at least (and all
their subtargets) work correctly with a parallel 'make'.
File: standards.info, Node: Utilities in Makefiles, Next: Command Variables, Prev: Makefile Basics, Up: Makefile Conventions
7.2.2 Utilities in Makefiles
----------------------------
Write the Makefile commands (and any shell scripts, such as 'configure')
to run under 'sh' (both the traditional Bourne shell and the POSIX
shell), not 'csh'. Don't use any special features of 'ksh' or 'bash',
or POSIX features not widely supported in traditional Bourne 'sh'.
The 'configure' script and the Makefile rules for building and
installation should not use any utilities directly except these:
awk cat cmp cp diff echo egrep expr false grep install-info ln ls
mkdir mv printf pwd rm rmdir sed sleep sort tar test touch tr true
Compression programs such as 'gzip' can be used in the 'dist' rule.
Generally, stick to the widely-supported (usually POSIX-specified)
options and features of these programs. For example, don't use 'mkdir
-p', convenient as it may be, because a few systems don't support it at
all and with others, it is not safe for parallel execution. For a list
of known incompatibilities, see *note Portable Shell Programming:
(autoconf)Portable Shell.
It is a good idea to avoid creating symbolic links in makefiles,
since a few file systems don't support them.
The Makefile rules for building and installation can also use
compilers and related programs, but should do so via 'make' variables so
that the user can substitute alternatives. Here are some of the
programs we mean:
ar bison cc flex install ld ldconfig lex
make makeinfo ranlib texi2dvi yacc
Use the following 'make' variables to run those programs:
$(AR) $(BISON) $(CC) $(FLEX) $(INSTALL) $(LD) $(LDCONFIG) $(LEX)
$(MAKE) $(MAKEINFO) $(RANLIB) $(TEXI2DVI) $(YACC)
When you use 'ranlib' or 'ldconfig', you should make sure nothing bad
happens if the system does not have the program in question. Arrange to
ignore an error from that command, and print a message before the
command to tell the user that failure of this command does not mean a
problem. (The Autoconf 'AC_PROG_RANLIB' macro can help with this.)
If you use symbolic links, you should implement a fallback for
systems that don't have symbolic links.
Additional utilities that can be used via Make variables are:
chgrp chmod chown mknod
It is ok to use other utilities in Makefile portions (or scripts)
intended only for particular systems where you know those utilities
exist.
File: standards.info, Node: Command Variables, Next: DESTDIR, Prev: Utilities in Makefiles, Up: Makefile Conventions
7.2.3 Variables for Specifying Commands
---------------------------------------
Makefiles should provide variables for overriding certain commands,
options, and so on.
In particular, you should run most utility programs via variables.
Thus, if you use Bison, have a variable named 'BISON' whose default
value is set with 'BISON = bison', and refer to it with '$(BISON)'
whenever you need to use Bison.
File management utilities such as 'ln', 'rm', 'mv', and so on, need
not be referred to through variables in this way, since users don't need
to replace them with other programs.
Each program-name variable should come with an options variable that
is used to supply options to the program. Append 'FLAGS' to the
program-name variable name to get the options variable name--for
example, 'BISONFLAGS'. (The names 'CFLAGS' for the C compiler, 'YFLAGS'
for yacc, and 'LFLAGS' for lex, are exceptions to this rule, but we keep
them because they are standard.) Use 'CPPFLAGS' in any compilation
command that runs the preprocessor, and use 'LDFLAGS' in any compilation
command that does linking as well as in any direct use of 'ld'.
If there are C compiler options that _must_ be used for proper
compilation of certain files, do not include them in 'CFLAGS'. Users
expect to be able to specify 'CFLAGS' freely themselves. Instead,
arrange to pass the necessary options to the C compiler independently of
'CFLAGS', by writing them explicitly in the compilation commands or by
defining an implicit rule, like this:
CFLAGS = -g
ALL_CFLAGS = -I. $(CFLAGS)
.c.o:
$(CC) -c $(CPPFLAGS) $(ALL_CFLAGS) $<
Do include the '-g' option in 'CFLAGS', because that is not
_required_ for proper compilation. You can consider it a default that
is only recommended. If the package is set up so that it is compiled
with GCC by default, then you might as well include '-O' in the default
value of 'CFLAGS' as well.
Put 'CFLAGS' last in the compilation command, after other variables
containing compiler options, so the user can use 'CFLAGS' to override
the others.
'CFLAGS' should be used in every invocation of the C compiler, both
those which do compilation and those which do linking.
Every Makefile should define the variable 'INSTALL', which is the
basic command for installing a file into the system.
Every Makefile should also define the variables 'INSTALL_PROGRAM' and
'INSTALL_DATA'. (The default for 'INSTALL_PROGRAM' should be
'$(INSTALL)'; the default for 'INSTALL_DATA' should be '${INSTALL} -m
644'.) Then it should use those variables as the commands for actual
installation, for executables and non-executables respectively. Minimal
use of these variables is as follows:
$(INSTALL_PROGRAM) foo $(bindir)/foo
$(INSTALL_DATA) libfoo.a $(libdir)/libfoo.a
However, it is preferable to support a 'DESTDIR' prefix on the target
files, as explained in the next section.
It is acceptable, but not required, to install multiple files in one
command, with the final argument being a directory, as in:
$(INSTALL_PROGRAM) foo bar baz $(bindir)
File: standards.info, Node: DESTDIR, Next: Directory Variables, Prev: Command Variables, Up: Makefile Conventions
7.2.4 'DESTDIR': Support for Staged Installs
--------------------------------------------
'DESTDIR' is a variable prepended to each installed target file, like
this:
$(INSTALL_PROGRAM) foo $(DESTDIR)$(bindir)/foo
$(INSTALL_DATA) libfoo.a $(DESTDIR)$(libdir)/libfoo.a
The 'DESTDIR' variable is specified by the user on the 'make' command
line as an absolute file name. For example:
make DESTDIR=/tmp/stage install
'DESTDIR' should be supported only in the 'install*' and 'uninstall*'
targets, as those are the only targets where it is useful.
If your installation step would normally install '/usr/local/bin/foo'
and '/usr/local/lib/libfoo.a', then an installation invoked as in the
example above would install '/tmp/stage/usr/local/bin/foo' and
'/tmp/stage/usr/local/lib/libfoo.a' instead.
Prepending the variable 'DESTDIR' to each target in this way provides
for "staged installs", where the installed files are not placed directly
into their expected location but are instead copied into a temporary
location ('DESTDIR'). However, installed files maintain their relative
directory structure and any embedded file names will not be modified.
You should not set the value of 'DESTDIR' in your 'Makefile' at all;
then the files are installed into their expected locations by default.
Also, specifying 'DESTDIR' should not change the operation of the
software in any way, so its value should not be included in any file
contents.
'DESTDIR' support is commonly used in package creation. It is also
helpful to users who want to understand what a given package will
install where, and to allow users who don't normally have permissions to
install into protected areas to build and install before gaining those
permissions. Finally, it can be useful with tools such as 'stow', where
code is installed in one place but made to appear to be installed
somewhere else using symbolic links or special mount operations. So, we
strongly recommend GNU packages support 'DESTDIR', though it is not an
absolute requirement.
File: standards.info, Node: Directory Variables, Next: Standard Targets, Prev: DESTDIR, Up: Makefile Conventions
7.2.5 Variables for Installation Directories
--------------------------------------------
Installation directories should always be named by variables, so it is
easy to install in a nonstandard place. The standard names for these
variables and the values they should have in GNU packages are described
below. They are based on a standard file system layout; variants of it
are used in GNU/Linux and other modern operating systems.
Installers are expected to override these values when calling 'make'
(e.g., 'make prefix=/usr install') or 'configure' (e.g., 'configure
--prefix=/usr'). GNU packages should not try to guess which value
should be appropriate for these variables on the system they are being
installed onto: use the default settings specified here so that all GNU
packages behave identically, allowing the installer to achieve any
desired layout.
All installation directories, and their parent directories, should be
created (if necessary) before they are installed into.
These first two variables set the root for the installation. All the
other installation directories should be subdirectories of one of these
two, and nothing should be directly installed into these two
directories.
'prefix'
A prefix used in constructing the default values of the variables
listed below. The default value of 'prefix' should be
'/usr/local'. When building the complete GNU system, the prefix
will be empty and '/usr' will be a symbolic link to '/'. (If you
are using Autoconf, write it as '@prefix@'.)
Running 'make install' with a different value of 'prefix' from the
one used to build the program should _not_ recompile the program.
'exec_prefix'
A prefix used in constructing the default values of some of the
variables listed below. The default value of 'exec_prefix' should
be '$(prefix)'. (If you are using Autoconf, write it as
'@exec_prefix@'.)
Generally, '$(exec_prefix)' is used for directories that contain
machine-specific files (such as executables and subroutine
libraries), while '$(prefix)' is used directly for other
directories.
Running 'make install' with a different value of 'exec_prefix' from
the one used to build the program should _not_ recompile the
program.
Executable programs are installed in one of the following
directories.
'bindir'
The directory for installing executable programs that users can
run. This should normally be '/usr/local/bin', but write it as
'$(exec_prefix)/bin'. (If you are using Autoconf, write it as
'@bindir@'.)
'sbindir'
The directory for installing executable programs that can be run
from the shell, but are only generally useful to system
administrators. This should normally be '/usr/local/sbin', but
write it as '$(exec_prefix)/sbin'. (If you are using Autoconf,
write it as '@sbindir@'.)
'libexecdir'
The directory for installing executable programs to be run by other
programs rather than by users. This directory should normally be
'/usr/local/libexec', but write it as '$(exec_prefix)/libexec'.
(If you are using Autoconf, write it as '@libexecdir@'.)
The definition of 'libexecdir' is the same for all packages, so you
should install your data in a subdirectory thereof. Most packages
install their data under '$(libexecdir)/PACKAGE-NAME/', possibly
within additional subdirectories thereof, such as
'$(libexecdir)/PACKAGE-NAME/MACHINE/VERSION'.
Data files used by the program during its execution are divided into
categories in two ways.
* Some files are normally modified by programs; others are never
normally modified (though users may edit some of these).
* Some files are architecture-independent and can be shared by all
machines at a site; some are architecture-dependent and can be
shared only by machines of the same kind and operating system;
others may never be shared between two machines.
This makes for six different possibilities. However, we want to
discourage the use of architecture-dependent files, aside from object
files and libraries. It is much cleaner to make other data files
architecture-independent, and it is generally not hard.
Here are the variables Makefiles should use to specify directories to
put these various kinds of files in:
'datarootdir'
The root of the directory tree for read-only
architecture-independent data files. This should normally be
'/usr/local/share', but write it as '$(prefix)/share'. (If you are
using Autoconf, write it as '@datarootdir@'.) 'datadir''s default
value is based on this variable; so are 'infodir', 'mandir', and
others.
'datadir'
The directory for installing idiosyncratic read-only
architecture-independent data files for this program. This is
usually the same place as 'datarootdir', but we use the two
separate variables so that you can move these program-specific
files without altering the location for Info files, man pages, etc.
This should normally be '/usr/local/share', but write it as
'$(datarootdir)'. (If you are using Autoconf, write it as
'@datadir@'.)
The definition of 'datadir' is the same for all packages, so you
should install your data in a subdirectory thereof. Most packages
install their data under '$(datadir)/PACKAGE-NAME/'.
'sysconfdir'
The directory for installing read-only data files that pertain to a
single machine-that is to say, files for configuring a host.
Mailer and network configuration files, '/etc/passwd', and so forth
belong here. All the files in this directory should be ordinary
ASCII text files. This directory should normally be
'/usr/local/etc', but write it as '$(prefix)/etc'. (If you are
using Autoconf, write it as '@sysconfdir@'.)
Do not install executables here in this directory (they probably
belong in '$(libexecdir)' or '$(sbindir)'). Also do not install
files that are modified in the normal course of their use (programs
whose purpose is to change the configuration of the system
excluded). Those probably belong in '$(localstatedir)'.
'sharedstatedir'
The directory for installing architecture-independent data files
which the programs modify while they run. This should normally be
'/usr/local/com', but write it as '$(prefix)/com'. (If you are
using Autoconf, write it as '@sharedstatedir@'.)
'localstatedir'
The directory for installing data files which the programs modify
while they run, and that pertain to one specific machine. Users
should never need to modify files in this directory to configure
the package's operation; put such configuration information in
separate files that go in '$(datadir)' or '$(sysconfdir)'.
'$(localstatedir)' should normally be '/usr/local/var', but write
it as '$(prefix)/var'. (If you are using Autoconf, write it as
'@localstatedir@'.)
'runstatedir'
The directory for installing data files which the programs modify
while they run, that pertain to one specific machine, and which
need not persist longer than the execution of the program--which is
generally long-lived, for example, until the next reboot. PID
files for system daemons are a typical use. In addition, this
directory should not be cleaned except perhaps at reboot, while the
general '/tmp' ('TMPDIR') may be cleaned arbitrarily. This should
normally be '/var/run', but write it as '$(localstatedir)/run'.
Having it as a separate variable allows the use of '/run' if
desired, for example. (If you are using Autoconf 2.70 or later,
write it as '@runstatedir@'.)
These variables specify the directory for installing certain specific
types of files, if your program has them. Every GNU package should have
Info files, so every program needs 'infodir', but not all need 'libdir'
or 'lispdir'.
'includedir'
The directory for installing header files to be included by user
programs with the C '#include' preprocessor directive. This should
normally be '/usr/local/include', but write it as
'$(prefix)/include'. (If you are using Autoconf, write it as
'@includedir@'.)
Most compilers other than GCC do not look for header files in
directory '/usr/local/include'. So installing the header files
this way is only useful with GCC. Sometimes this is not a problem
because some libraries are only really intended to work with GCC.
But some libraries are intended to work with other compilers. They
should install their header files in two places, one specified by
'includedir' and one specified by 'oldincludedir'.
'oldincludedir'
The directory for installing '#include' header files for use with
compilers other than GCC. This should normally be '/usr/include'.
(If you are using Autoconf, you can write it as '@oldincludedir@'.)
The Makefile commands should check whether the value of
'oldincludedir' is empty. If it is, they should not try to use it;
they should cancel the second installation of the header files.
A package should not replace an existing header in this directory
unless the header came from the same package. Thus, if your Foo
package provides a header file 'foo.h', then it should install the
header file in the 'oldincludedir' directory if either (1) there is
no 'foo.h' there or (2) the 'foo.h' that exists came from the Foo
package.
To tell whether 'foo.h' came from the Foo package, put a magic
string in the file--part of a comment--and 'grep' for that string.
'docdir'
The directory for installing documentation files (other than Info)
for this package. By default, it should be
'/usr/local/share/doc/YOURPKG', but it should be written as
'$(datarootdir)/doc/YOURPKG'. (If you are using Autoconf, write it
as '@docdir@'.) The YOURPKG subdirectory, which may include a
version number, prevents collisions among files with common names,
such as 'README'.
'infodir'
The directory for installing the Info files for this package. By
default, it should be '/usr/local/share/info', but it should be
written as '$(datarootdir)/info'. (If you are using Autoconf,
write it as '@infodir@'.) 'infodir' is separate from 'docdir' for
compatibility with existing practice.
'htmldir'
'dvidir'
'pdfdir'
'psdir'
Directories for installing documentation files in the particular
format. They should all be set to '$(docdir)' by default. (If you
are using Autoconf, write them as '@htmldir@', '@dvidir@', etc.)
Packages which supply several translations of their documentation
should install them in '$(htmldir)/'LL, '$(pdfdir)/'LL, etc. where
LL is a locale abbreviation such as 'en' or 'pt_BR'.
'libdir'
The directory for object files and libraries of object code. Do
not install executables here, they probably ought to go in
'$(libexecdir)' instead. The value of 'libdir' should normally be
'/usr/local/lib', but write it as '$(exec_prefix)/lib'. (If you
are using Autoconf, write it as '@libdir@'.)
'lispdir'
The directory for installing any Emacs Lisp files in this package.
By default, it should be '/usr/local/share/emacs/site-lisp', but it
should be written as '$(datarootdir)/emacs/site-lisp'.
If you are using Autoconf, write the default as '@lispdir@'. In
order to make '@lispdir@' work, you need the following lines in
your 'configure.ac' file:
lispdir='${datarootdir}/emacs/site-lisp'
AC_SUBST(lispdir)
'localedir'
The directory for installing locale-specific message catalogs for
this package. By default, it should be '/usr/local/share/locale',
but it should be written as '$(datarootdir)/locale'. (If you are
using Autoconf, write it as '@localedir@'.) This directory usually
has a subdirectory per locale.
Unix-style man pages are installed in one of the following:
'mandir'
The top-level directory for installing the man pages (if any) for
this package. It will normally be '/usr/local/share/man', but you
should write it as '$(datarootdir)/man'. (If you are using
Autoconf, write it as '@mandir@'.)
'man1dir'
The directory for installing section 1 man pages. Write it as
'$(mandir)/man1'.
'man2dir'
The directory for installing section 2 man pages. Write it as
'$(mandir)/man2'
'...'
*Don't make the primary documentation for any GNU software be a man
page. Write a manual in Texinfo instead. Man pages are just for
the sake of people running GNU software on Unix, which is a
secondary application only.*
'manext'
The file name extension for the installed man page. This should
contain a period followed by the appropriate digit; it should
normally be '.1'.
'man1ext'
The file name extension for installed section 1 man pages.
'man2ext'
The file name extension for installed section 2 man pages.
'...'
Use these names instead of 'manext' if the package needs to install
man pages in more than one section of the manual.
And finally, you should set the following variable:
'srcdir'
The directory for the sources being compiled. The value of this
variable is normally inserted by the 'configure' shell script. (If
you are using Autoconf, use 'srcdir = @srcdir@'.)
For example:
# Common prefix for installation directories.
# NOTE: This directory must exist when you start the install.
prefix = /usr/local
datarootdir = $(prefix)/share
datadir = $(datarootdir)
exec_prefix = $(prefix)
# Where to put the executable for the command 'gcc'.
bindir = $(exec_prefix)/bin
# Where to put the directories used by the compiler.
libexecdir = $(exec_prefix)/libexec
# Where to put the Info files.
infodir = $(datarootdir)/info
If your program installs a large number of files into one of the
standard user-specified directories, it might be useful to group them
into a subdirectory particular to that program. If you do this, you
should write the 'install' rule to create these subdirectories.
Do not expect the user to include the subdirectory name in the value
of any of the variables listed above. The idea of having a uniform set
of variable names for installation directories is to enable the user to
specify the exact same values for several different GNU packages. In
order for this to be useful, all the packages must be designed so that
they will work sensibly when the user does so.
At times, not all of these variables may be implemented in the
current release of Autoconf and/or Automake; but as of Autoconf 2.60, we
believe all of them are. When any are missing, the descriptions here
serve as specifications for what Autoconf will implement. As a
programmer, you can either use a development version of Autoconf or
avoid using these variables until a stable release is made which
supports them.
File: standards.info, Node: Standard Targets, Next: Install Command Categories, Prev: Directory Variables, Up: Makefile Conventions
7.2.6 Standard Targets for Users
--------------------------------
All GNU programs should have the following targets in their Makefiles:
'all'
Compile the entire program. This should be the default target.
This target need not rebuild any documentation files; Info files
should normally be included in the distribution, and DVI (and other
documentation format) files should be made only when explicitly
asked for.
By default, the Make rules should compile and link with '-g', so
that executable programs have debugging symbols. Otherwise, you
are essentially helpless in the face of a crash, and it is often
far from easy to reproduce with a fresh build.
'install'
Compile the program and copy the executables, libraries, and so on
to the file names where they should reside for actual use. If
there is a simple test to verify that a program is properly
installed, this target should run that test.
Do not strip executables when installing them. This helps eventual
debugging that may be needed later, and nowadays disk space is
cheap and dynamic loaders typically ensure debug sections are not
loaded during normal execution. Users that need stripped binaries
may invoke the 'install-strip' target to do that.
If possible, write the 'install' target rule so that it does not
modify anything in the directory where the program was built,
provided 'make all' has just been done. This is convenient for
building the program under one user name and installing it under
another.
The commands should create all the directories in which files are
to be installed, if they don't already exist. This includes the
directories specified as the values of the variables 'prefix' and
'exec_prefix', as well as all subdirectories that are needed. One
way to do this is by means of an 'installdirs' target as described
below.
Use '-' before any command for installing a man page, so that
'make' will ignore any errors. This is in case there are systems
that don't have the Unix man page documentation system installed.
The way to install Info files is to copy them into '$(infodir)'
with '$(INSTALL_DATA)' (*note Command Variables::), and then run
the 'install-info' program if it is present. 'install-info' is a
program that edits the Info 'dir' file to add or update the menu
entry for the given Info file; it is part of the Texinfo package.
Here is a sample rule to install an Info file that also tries to
handle some additional situations, such as 'install-info' not being
present.
do-install-info: foo.info installdirs
$(NORMAL_INSTALL)
# Prefer an info file in . to one in srcdir.
if test -f foo.info; then d=.; \
else d="$(srcdir)"; fi; \
$(INSTALL_DATA) $$d/foo.info \
"$(DESTDIR)$(infodir)/foo.info"
# Run install-info only if it exists.
# Use 'if' instead of just prepending '-' to the
# line so we notice real errors from install-info.
# Use '$(SHELL) -c' because some shells do not
# fail gracefully when there is an unknown command.
$(POST_INSTALL)
if $(SHELL) -c 'install-info --version' \
>/dev/null 2>&1; then \
install-info --dir-file="$(DESTDIR)$(infodir)/dir" \
"$(DESTDIR)$(infodir)/foo.info"; \
else true; fi
When writing the 'install' target, you must classify all the
commands into three categories: normal ones, "pre-installation"
commands and "post-installation" commands. *Note Install Command
Categories::.
'install-html'
'install-dvi'
'install-pdf'
'install-ps'
These targets install documentation in formats other than Info;
they're intended to be called explicitly by the person installing
the package, if that format is desired. GNU prefers Info files, so
these must be installed by the 'install' target.
When you have many documentation files to install, we recommend
that you avoid collisions and clutter by arranging for these
targets to install in subdirectories of the appropriate
installation directory, such as 'htmldir'. As one example, if your
package has multiple manuals, and you wish to install HTML
documentation with many files (such as the "split" mode output by
'makeinfo --html'), you'll certainly want to use subdirectories, or
two nodes with the same name in different manuals will overwrite
each other.
Please make these 'install-FORMAT' targets invoke the commands for
the FORMAT target, for example, by making FORMAT a dependency.
'uninstall'
Delete all the installed files--the copies that the 'install' and
'install-*' targets create.
This rule should not modify the directories where compilation is
done, only the directories where files are installed.
The uninstallation commands are divided into three categories, just
like the installation commands. *Note Install Command
Categories::.
'install-strip'
Like 'install', but strip the executable files while installing
them. In simple cases, this target can use the 'install' target in
a simple way:
install-strip:
$(MAKE) INSTALL_PROGRAM='$(INSTALL_PROGRAM) -s' \
install
But if the package installs scripts as well as real executables,
the 'install-strip' target can't just refer to the 'install'
target; it has to strip the executables but not the scripts.
'install-strip' should not strip the executables in the build
directory which are being copied for installation. It should only
strip the copies that are installed.
Normally we do not recommend stripping an executable unless you are
sure the program has no bugs. However, it can be reasonable to
install a stripped executable for actual execution while saving the
unstripped executable elsewhere in case there is a bug.
'clean'
Delete all files in the current directory that are normally created
by building the program. Also delete files in other directories if
they are created by this makefile. However, don't delete the files
that record the configuration. Also preserve files that could be
made by building, but normally aren't because the distribution
comes with them. There is no need to delete parent directories
that were created with 'mkdir -p', since they could have existed
anyway.
Delete '.dvi' files here if they are not part of the distribution.
'distclean'
Delete all files in the current directory (or created by this
makefile) that are created by configuring or building the program.
If you have unpacked the source and built the program without
creating any other files, 'make distclean' should leave only the
files that were in the distribution. However, there is no need to
delete parent directories that were created with 'mkdir -p', since
they could have existed anyway.
'mostlyclean'
Like 'clean', but may refrain from deleting a few files that people
normally don't want to recompile. For example, the 'mostlyclean'
target for GCC does not delete 'libgcc.a', because recompiling it
is rarely necessary and takes a lot of time.
'maintainer-clean'
Delete almost everything that can be reconstructed with this
Makefile. This typically includes everything deleted by
'distclean', plus more: C source files produced by Bison, tags
tables, Info files, and so on.
The reason we say "almost everything" is that running the command
'make maintainer-clean' should not delete 'configure' even if
'configure' can be remade using a rule in the Makefile. More
generally, 'make maintainer-clean' should not delete anything that
needs to exist in order to run 'configure' and then begin to build
the program. Also, there is no need to delete parent directories
that were created with 'mkdir -p', since they could have existed
anyway. These are the only exceptions; 'maintainer-clean' should
delete everything else that can be rebuilt.
The 'maintainer-clean' target is intended to be used by a
maintainer of the package, not by ordinary users. You may need
special tools to reconstruct some of the files that 'make
maintainer-clean' deletes. Since these files are normally included
in the distribution, we don't take care to make them easy to
reconstruct. If you find you need to unpack the full distribution
again, don't blame us.
To help make users aware of this, the commands for the special
'maintainer-clean' target should start with these two:
@echo 'This command is intended for maintainers to use; it'
@echo 'deletes files that may need special tools to rebuild.'
'TAGS'
Update a tags table for this program.
'info'
Generate any Info files needed. The best way to write the rules is
as follows:
info: foo.info
foo.info: foo.texi chap1.texi chap2.texi
$(MAKEINFO) $(srcdir)/foo.texi
You must define the variable 'MAKEINFO' in the Makefile. It should
run the 'makeinfo' program, which is part of the Texinfo
distribution.
Normally a GNU distribution comes with Info files, and that means
the Info files are present in the source directory. Therefore, the
Make rule for an info file should update it in the source
directory. When users build the package, ordinarily Make will not
update the Info files because they will already be up to date.
'dvi'
'html'
'pdf'
'ps'
Generate documentation files in the given format. These targets
should always exist, but any or all can be a no-op if the given
output format cannot be generated. These targets should not be
dependencies of the 'all' target; the user must manually invoke
them.
Here's an example rule for generating DVI files from Texinfo:
dvi: foo.dvi
foo.dvi: foo.texi chap1.texi chap2.texi
$(TEXI2DVI) $(srcdir)/foo.texi
You must define the variable 'TEXI2DVI' in the Makefile. It should
run the program 'texi2dvi', which is part of the Texinfo
distribution. ('texi2dvi' uses TeX to do the real work of
formatting. TeX is not distributed with Texinfo.) Alternatively,
write only the dependencies, and allow GNU 'make' to provide the
command.
Here's another example, this one for generating HTML from Texinfo:
html: foo.html
foo.html: foo.texi chap1.texi chap2.texi
$(TEXI2HTML) $(srcdir)/foo.texi
Again, you would define the variable 'TEXI2HTML' in the Makefile;
for example, it might run 'makeinfo --no-split --html' ('makeinfo'
is part of the Texinfo distribution).
'dist'
Create a distribution tar file for this program. The tar file
should be set up so that the file names in the tar file start with
a subdirectory name which is the name of the package it is a
distribution for. This name can include the version number.
For example, the distribution tar file of GCC version 1.40 unpacks
into a subdirectory named 'gcc-1.40'.
The easiest way to do this is to create a subdirectory
appropriately named, use 'ln' or 'cp' to install the proper files
in it, and then 'tar' that subdirectory.
Compress the tar file with 'gzip'. For example, the actual
distribution file for GCC version 1.40 is called 'gcc-1.40.tar.gz'.
It is ok to support other free compression formats as well.
The 'dist' target should explicitly depend on all non-source files
that are in the distribution, to make sure they are up to date in
the distribution. *Note Making Releases: Releases.
'check'
Perform self-tests (if any). The user must build the program
before running the tests, but need not install the program; you
should write the self-tests so that they work when the program is
built but not installed.
The following targets are suggested as conventional names, for
programs in which they are useful.
'installcheck'
Perform installation tests (if any). The user must build and
install the program before running the tests. You should not
assume that '$(bindir)' is in the search path.
'installdirs'
It's useful to add a target named 'installdirs' to create the
directories where files are installed, and their parent
directories. There is a script called 'mkinstalldirs' which is
convenient for this; you can find it in the Gnulib package. You
can use a rule like this:
# Make sure all installation directories (e.g. $(bindir))
# actually exist by making them if necessary.
installdirs: mkinstalldirs
$(srcdir)/mkinstalldirs $(bindir) $(datadir) \
$(libdir) $(infodir) \
$(mandir)
or, if you wish to support 'DESTDIR' (strongly encouraged),
# Make sure all installation directories (e.g. $(bindir))
# actually exist by making them if necessary.
installdirs: mkinstalldirs
$(srcdir)/mkinstalldirs \
$(DESTDIR)$(bindir) $(DESTDIR)$(datadir) \
$(DESTDIR)$(libdir) $(DESTDIR)$(infodir) \
$(DESTDIR)$(mandir)
This rule should not modify the directories where compilation is
done. It should do nothing but create installation directories.
File: standards.info, Node: Install Command Categories, Prev: Standard Targets, Up: Makefile Conventions
7.2.7 Install Command Categories
--------------------------------
When writing the 'install' target, you must classify all the commands
into three categories: normal ones, "pre-installation" commands and
"post-installation" commands.
Normal commands move files into their proper places, and set their
modes. They may not alter any files except the ones that come entirely
from the package they belong to.
Pre-installation and post-installation commands may alter other
files; in particular, they can edit global configuration files or data
bases.
Pre-installation commands are typically executed before the normal
commands, and post-installation commands are typically run after the
normal commands.
The most common use for a post-installation command is to run
'install-info'. This cannot be done with a normal command, since it
alters a file (the Info directory) which does not come entirely and
solely from the package being installed. It is a post-installation
command because it needs to be done after the normal command which
installs the package's Info files.
Most programs don't need any pre-installation commands, but we have
the feature just in case it is needed.
To classify the commands in the 'install' rule into these three
categories, insert "category lines" among them. A category line
specifies the category for the commands that follow.
A category line consists of a tab and a reference to a special Make
variable, plus an optional comment at the end. There are three
variables you can use, one for each category; the variable name
specifies the category. Category lines are no-ops in ordinary execution
because these three Make variables are normally undefined (and you
_should not_ define them in the makefile).
Here are the three possible category lines, each with a comment that
explains what it means:
$(PRE_INSTALL) # Pre-install commands follow.
$(POST_INSTALL) # Post-install commands follow.
$(NORMAL_INSTALL) # Normal commands follow.
If you don't use a category line at the beginning of the 'install'
rule, all the commands are classified as normal until the first category
line. If you don't use any category lines, all the commands are
classified as normal.
These are the category lines for 'uninstall':
$(PRE_UNINSTALL) # Pre-uninstall commands follow.
$(POST_UNINSTALL) # Post-uninstall commands follow.
$(NORMAL_UNINSTALL) # Normal commands follow.
Typically, a pre-uninstall command would be used for deleting entries
from the Info directory.
If the 'install' or 'uninstall' target has any dependencies which act
as subroutines of installation, then you should start _each_
dependency's commands with a category line, and start the main target's
commands with a category line also. This way, you can ensure that each
command is placed in the right category regardless of which of the
dependencies actually run.
Pre-installation and post-installation commands should not run any
programs except for these:
[ basename bash cat chgrp chmod chown cmp cp dd diff echo
egrep expand expr false fgrep find getopt grep gunzip gzip
hostname install install-info kill ldconfig ln ls md5sum
mkdir mkfifo mknod mv printenv pwd rm rmdir sed sort tee
test touch true uname xargs yes
The reason for distinguishing the commands in this way is for the
sake of making binary packages. Typically a binary package contains all
the executables and other files that need to be installed, and has its
own method of installing them--so it does not need to run the normal
installation commands. But installing the binary package does need to
execute the pre-installation and post-installation commands.
Programs to build binary packages work by extracting the
pre-installation and post-installation commands. Here is one way of
extracting the pre-installation commands (the '-s' option to 'make' is
needed to silence messages about entering subdirectories):
make -s -n install -o all \
PRE_INSTALL=pre-install \
POST_INSTALL=post-install \
NORMAL_INSTALL=normal-install \
| gawk -f pre-install.awk
where the file 'pre-install.awk' could contain this:
$0 ~ /^(normal-install|post-install)[ \t]*$/ {on = 0}
on {print $0}
$0 ~ /^pre-install[ \t]*$/ {on = 1}
File: standards.info, Node: Releases, Prev: Makefile Conventions, Up: Managing Releases
7.3 Making 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.
Package the distribution of 'Foo version 69.96' up in a gzipped tar
file with the name 'foo-69.96.tar.gz'. It should unpack into a
subdirectory named 'foo-69.96'.
Building and installing the program should never modify any of the
files contained in the distribution. This means that all the files that
form part of the program in any way must be classified into "source
files" and "non-source files". Source files are written by humans and
never changed automatically; non-source files are produced from source
files by programs under the control of the Makefile.
The distribution should contain a file named 'README' with a general
overview of the package:
* the name of the package;
* the version number of the package, or refer to where in the package
the version can be found;
* a general description of what the package does;
* a reference to the file 'INSTALL', which should in turn contain an
explanation of the installation procedure;
* a brief explanation of any unusual top-level directories or files,
or other hints for readers to find their way around the source;
* a reference to the file which contains the copying conditions. The
GNU GPL, if used, should be in a file called 'COPYING'. If the GNU
LGPL is used, it should be in a file called 'COPYING.LESSER'.
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, 'flex',
TeX, and 'makeinfo'; this helps avoid unnecessary dependencies between
our distributions, so that users can 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 *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 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
'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
systems that don't support symbolic links. Also, don't use multiple
names for one file in different directories, because certain file
systems cannot handle this and that prevents unpacking the distribution.
Try to make sure that all the file names will be unique on MS-DOS. A
name on MS-DOS consists of up to 8 characters, optionally followed by a
period and up to three characters. MS-DOS will truncate extra
characters both before and after the period. Thus, 'foobarhacker.c' and
'foobarhacker.o' are not ambiguous; they are truncated to 'foobarha.c'
and 'foobarha.o', which are distinct.
Include in your distribution a copy of the 'texinfo.tex' you used to
test print any '*.texinfo' or '*.texi' files.
Likewise, if your program uses small GNU software packages like
regex, getopt, obstack, or termcap, include them in the distribution
file. Leaving them out would make the distribution file a little
smaller at the expense of possible inconvenience to a user who doesn't
know what other files to get.
File: standards.info, Node: References, Next: GNU Free Documentation License, Prev: Managing Releases, Up: Top
8 References to Non-Free Software and Documentation
***************************************************
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, 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
<http://www.gnu.org/philosophy/free-sw.html>;, and the definition of free
documentation is found at <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
<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 <licensing AT 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
probably already know about it. For instance, it is fine to explain how
to build your package on top of some widely used non-free operating
system, or how to use it together with some widely used non-free
program.
However, you should give only the necessary information to help those
who already use the non-free program to use your program with it--don't
give, or refer to, any further information about the proprietary
program, and don't imply that the proprietary program enhances your
program, or that its existence is in any way a good 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 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 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 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 'mplayer'. It is free software in itself, and the
free code can handle some kinds of files. However, 'mplayer' recommends
use of non-free codecs for other kinds of files, and users that install
'mplayer' are very likely to install those codecs along with it. To
recommend '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 '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 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 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 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
page P that links to AT&T's site presenting it as a place to get some
non-free program, because that part of the page P itself recommends and
legitimizes the non-free program. However, that P 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.
A web page recommends a program in a particularly strong way if it
requires users to run that program in order to use the page. Many pages
contain Javascript code which they recommend in this way. This
Javascript code may be free or nonfree, but nonfree is the usual case.
If the purpose for which you would refer to the page cannot be
carried out without running nonfree Javascript code, then you should not
refer to it. Thus, if the purpose of referring to the page is for
people to view a video, or subscribing to a mailing list, and the
viewing or subscribing fail to work if the user's browser blocks the
nonfree Javascript code, then don't refer to that page.
The extreme case is that of web sites which depend on nonfree
Javascript code even to _see_ the contents of the pages. Any site
hosted on 'wix.com' has this problem, and so do some other sites.
Referring people to such pages to read their contents is, in effect,
urging them to run those nonfree programs--so please don't refer to
those pages. (Such pages also break the Web, so they deserve
condemnation for two reasons.)
Instead, please quote excerpts from the page to make your point, or
find another place to refer to that information.
File: standards.info, Node: GNU Free Documentation License, Next: Index, Prev: References, Up: Top
Appendix A GNU Free Documentation License
*****************************************
Version 1.3, 3 November 2008
Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
<http://fsf.org/>;
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless
of subject matter or whether it is published as a printed book. We
recommend this License principally for works whose purpose is
instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium,
that contains a notice placed by the copyright holder saying it can
be distributed under the terms of this License. Such a notice
grants a world-wide, royalty-free license, unlimited in duration,
to use that work under the conditions stated herein. The
"Document", below, refers to any such manual or work. Any member
of the public is a licensee, and is addressed as "you". You accept
the license if you copy, modify or distribute the work in a way
requiring permission under copyright law.
A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section
of the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall
subject (or to related matters) and contains nothing that could
fall directly within that overall subject. (Thus, if the Document
is in part a textbook of mathematics, a Secondary Section may not
explain any mathematics.) The relationship could be a matter of
historical connection with the subject or with related matters, or
of legal, commercial, philosophical, ethical or political position
regarding them.
The "Invariant Sections" are certain Secondary Sections whose
titles are designated, as being those of Invariant Sections, in the
notice that says that the Document is released under this License.
If a section does not fit the above definition of Secondary then it
is not allowed to be designated as Invariant. The Document may
contain zero Invariant Sections. If the Document does not identify
any Invariant Sections then there are none.
The "Cover Texts" are certain short passages of text that are
listed, as Front-Cover Texts or Back-Cover Texts, in the notice
that says that the Document is released under this License. A
Front-Cover Text may be at most 5 words, and a Back-Cover Text may
be at most 25 words.
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images composed
of pixels) generic paint programs or (for drawings) some widely
available drawing editor, and that is suitable for input to text
formatters or for automatic translation to a variety of formats
suitable for input to text formatters. A copy made in an otherwise
Transparent file format whose markup, or absence of markup, has
been arranged to thwart or discourage subsequent modification by
readers is not Transparent. An image format is not Transparent if
used for any substantial amount of text. A copy that is not
"Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format,
SGML or XML using a publicly available DTD, and standard-conforming
simple HTML, PostScript or PDF designed for human modification.
Examples of transparent image formats include PNG, XCF and JPG.
Opaque formats include proprietary formats that can be read and
edited only by proprietary word processors, SGML or XML for which
the DTD and/or processing tools are not generally available, and
the machine-generated HTML, PostScript or PDF produced by some word
processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the
material this License requires to appear in the title page. For
works in formats which do not have any title page as such, "Title
Page" means the text near the most prominent appearance of the
work's title, preceding the beginning of the body of the text.
The "publisher" means any person or entity that distributes copies
of the Document to the public.
A section "Entitled XYZ" means a named subunit of the Document
whose title either is precisely XYZ or contains XYZ in parentheses
following text that translates XYZ in another language. (Here XYZ
stands for a specific section name mentioned below, such as
"Acknowledgements", "Dedications", "Endorsements", or "History".)
To "Preserve the Title" of such a section when you modify the
Document means that it remains a section "Entitled XYZ" according
to this definition.
The Document may include Warranty Disclaimers next to the notice
which states that this License applies to the Document. These
Warranty Disclaimers are considered to be included by reference in
this License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and
has no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License
applies to the Document are reproduced in all copies, and that you
add no other conditions whatsoever to those of this License. You
may not use technical measures to obstruct or control the reading
or further copying of the copies you make or distribute. However,
you may accept compensation in exchange for copies. If you
distribute a large enough number of copies you must also follow the
conditions in section 3.
You may also lend copies, under the same conditions stated above,
and you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly
have printed covers) of the Document, numbering more than 100, and
the Document's license notice requires Cover Texts, you must
enclose the copies in covers that carry, clearly and legibly, all
these Cover Texts: Front-Cover Texts on the front cover, and
Back-Cover Texts on the back cover. Both covers must also clearly
and legibly identify you as the publisher of these copies. The
front cover must present the full title with all words of the title
equally prominent and visible. You may add other material on the
covers in addition. Copying with changes limited to the covers, as
long as they preserve the title of the Document and satisfy these
conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto
adjacent pages.
If you publish or distribute Opaque copies of the Document
numbering more than 100, you must either include a machine-readable
Transparent copy along with each Opaque copy, or state in or with
each Opaque copy a computer-network location from which the general
network-using public has access to download using public-standard
network protocols a complete Transparent copy of the Document, free
of added material. If you use the latter option, you must take
reasonably prudent steps, when you begin distribution of Opaque
copies in quantity, to ensure that this Transparent copy will
remain thus accessible at the stated location until at least one
year after the last time you distribute an Opaque copy (directly or
through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of
the Document well before redistributing any large number of copies,
to give them a chance to provide you with an updated version of the
Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document
under the conditions of sections 2 and 3 above, provided that you
release the Modified Version under precisely this License, with the
Modified Version filling the role of the Document, thus licensing
distribution and modification of the Modified Version to whoever
possesses a copy of it. In addition, you must do these things in
the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title
distinct from that of the Document, and from those of previous
versions (which should, if there were any, be listed in the
History section of the Document). You may use the same title
as a previous version if the original publisher of that
version gives permission.
B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in
the Modified Version, together with at least five of the
principal authors of the Document (all of its principal
authors, if it has fewer than five), unless they release you
from this requirement.
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified
Version under the terms of this License, in the form shown in
the Addendum below.
G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's
license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title,
and add to it an item stating at least the title, year, new
authors, and publisher of the Modified Version as given on the
Title Page. If there is no section Entitled "History" in the
Document, create one stating the title, year, authors, and
publisher of the Document as given on its Title Page, then add
an item describing the Modified Version as stated in the
previous sentence.
J. Preserve the network location, if any, given in the Document
for public access to a Transparent copy of the Document, and
likewise the network locations given in the Document for
previous versions it was based on. These may be placed in the
"History" section. You may omit a network location for a work
that was published at least four years before the Document
itself, or if the original publisher of the version it refers
to gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the section
all the substance and tone of each of the contributor
acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document, unaltered
in their text and in their titles. Section numbers or the
equivalent are not considered part of the section titles.
M. Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled
"Endorsements" or to conflict in title with any Invariant
Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no
material copied from the Document, you may at your option designate
some or all of these sections as invariant. To do this, add their
titles to the list of Invariant Sections in the Modified Version's
license notice. These titles must be distinct from any other
section titles.
You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text
has been approved by an organization as the authoritative
definition of a standard.
You may add a passage of up to five words as a Front-Cover Text,
and a passage of up to 25 words as a Back-Cover Text, to the end of
the list of Cover Texts in the Modified Version. Only one passage
of Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity. If the Document
already includes a cover text for the same cover, previously added
by you or by arrangement made by the same entity you are acting on
behalf of, you may not add another; but you may replace the old
one, on explicit permission from the previous publisher that added
the old one.
The author(s) and publisher(s) of the Document do not by this
License give permission to use their names for publicity for or to
assert or imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under
this License, under the terms defined in section 4 above for
modified versions, provided that you include in the combination all
of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your
combined work in its license notice, and that you preserve all
their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name
but different contents, make the title of each such section unique
by adding at the end of it, in parentheses, the name of the
original author or publisher of that section if known, or else a
unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the
combined work.
In the combination, you must combine any sections Entitled
"History" in the various original documents, forming one section
Entitled "History"; likewise combine any sections Entitled
"Acknowledgements", and any sections Entitled "Dedications". You
must delete all sections Entitled "Endorsements."
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the
rules of this License for verbatim copying of each of the documents
in all other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert
a copy of this License into the extracted document, and follow this
License in all other respects regarding verbatim copying of that
document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of a
storage or distribution medium, is called an "aggregate" if the
copyright resulting from the compilation is not used to limit the
legal rights of the compilation's users beyond what the individual
works permit. When the Document is included in an aggregate, this
License does not apply to the other works in the aggregate which
are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half
of the entire aggregate, the Document's Cover Texts may be placed
on covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic
form. Otherwise they must appear on printed covers that bracket
the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also
include the original English version of this License and the
original versions of those notices and disclaimers. In case of a
disagreement between the translation and the original version of
this License or a notice or disclaimer, the original version will
prevail.
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to
Preserve its Title (section 1) will typically require changing the
actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense, or distribute it is void,
and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your
license from a particular copyright holder is reinstated (a)
provisionally, unless and until the copyright holder explicitly and
finally terminates your license, and (b) permanently, if the
copyright holder fails to notify you of the violation by some
reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from
that copyright holder, and you cure the violation prior to 30 days
after your receipt of the notice.
Termination of your rights under this section does not terminate
the licenses of parties who have received copies or rights from you
under this License. If your rights have been terminated and not
permanently reinstated, receipt of a copy of some or all of the
same material does not give you any rights to use it.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of
the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
<http://www.gnu.org/copyleft/>;.
Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
version of this License "or any later version" applies to it, you
have the option of following the terms and conditions either of
that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If the
Document does not specify a version number of this License, you may
choose any version ever published (not as a draft) by the Free
Software Foundation. If the Document specifies that a proxy can
decide which future versions of this License can be used, that
proxy's public statement of acceptance of a version permanently
authorizes you to choose that version for the Document.
11. RELICENSING
"Massive Multiauthor Collaboration Site" (or "MMC Site") means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server.
A "Massive Multiauthor Collaboration" (or "MMC") contained in the
site means any set of copyrightable works thus published on the MMC
site.
"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.
"Incorporate" means to publish or republish a Document, in whole or
in part, as part of another Document.
An MMC is "eligible for relicensing" if it is licensed under this
License, and if all works that were first published under this
License somewhere other than this MMC, and subsequently
incorporated in whole or in part into the MMC, (1) had no cover
texts or invariant sections, and (2) were thus incorporated prior
to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the
site under CC-BY-SA on the same site at any time before August 1,
2009, provided the MMC is eligible for relicensing.
ADDENDUM: How to use this License for your documents
====================================================
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:
Copyright (C) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
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, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with
the Front-Cover Texts being LIST, and with the Back-Cover Texts
being LIST.
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of free
software license, such as the GNU General Public License, to permit
their use in free software.
File: standards.info, Node: Index, Prev: GNU Free Documentation License, Up: Top
Index
*****
* Menu:
* #endif, commenting: Comments. (line 60)
* --help output: --help. (line 6)
* --version output: --version. (line 6)
* -Wall compiler option: Syntactic Conventions.
(line 10)
* accepting contributions: Contributions. (line 6)
* address for bug reports: --help. (line 11)
* ANSI C standard: Standard C. (line 6)
* arbitrary limits on data: Semantics. (line 6)
* ASCII characters: Character Set. (line 6)
* autoconf: System Portability. (line 23)
* avoiding proprietary code: Reading Non-Free Code.
(line 6)
* batch of changes: Change Log Concepts. (line 6)
* behavior, dependent on program's name: User Interfaces. (line 6)
* binary packages: Install Command Categories.
(line 80)
* bindir: Directory Variables. (line 57)
* braces, in C source: Formatting. (line 9)
* bug reports: --help. (line 11)
* bug-standards AT gnu.org email address: Preface. (line 30)
* C compatibility: Compatibility. (line 6)
* C library functions, and portability: System Functions. (line 6)
* canonical name of a program: --version. (line 12)
* casting pointers to integers: CPU Portability. (line 49)
* CGI programs, standard options for: Command-Line Interfaces.
(line 31)
* change logs: Change Logs. (line 6)
* change logs, conditional changes: Conditional Changes. (line 6)
* change logs, style: Style of Change Logs.
(line 6)
* change set: Change Log Concepts. (line 6)
* character set: Character Set. (line 6)
* clang: Syntactic Conventions.
(line 17)
* command-line arguments, decoding: Semantics. (line 37)
* command-line interface: Command-Line Interfaces.
(line 6)
* commenting: Comments. (line 6)
* compatibility with C and POSIX standards: Compatibility. (line 6)
* compiler warnings: Syntactic Conventions.
(line 10)
* conditional changes, and change logs: Conditional Changes. (line 6)
* conditionals, comments for: Comments. (line 60)
* configure: Configuration. (line 6)
* control-L: Formatting. (line 131)
* conventions for makefiles: Makefile Conventions.
(line 6)
* CORBA: Graphical Interfaces.
(line 17)
* credits for manuals: Manual Credits. (line 6)
* D-bus: Graphical Interfaces.
(line 17)
* data structures, in Gnulib: System Functions. (line 44)
* data types, and portability: CPU Portability. (line 6)
* description, change log entry: Change Log Concepts. (line 12)
* DESTDIR: DESTDIR. (line 6)
* directories, creating installation: Directory Variables. (line 20)
* documentation: Documentation. (line 6)
* doschk: Names. (line 38)
* double quote: Quote Characters. (line 6)
* downloading this manual: Preface. (line 14)
* dynamic plug-ins: Dynamic Plug-In Interfaces.
(line 6)
* encodings: Character Set. (line 6)
* enum types, formatting: Formatting. (line 48)
* error messages: Semantics. (line 16)
* error messages, formatting: Errors. (line 6)
* error messages, in Gnulib: System Functions. (line 44)
* exec_prefix: Directory Variables. (line 39)
* expressions, splitting: Formatting. (line 94)
* FDL, GNU Free Documentation License: GNU Free Documentation License.
(line 6)
* file usage: File Usage. (line 6)
* file-name limitations: Names. (line 38)
* formatting error messages: Errors. (line 6)
* formatting source code: Formatting. (line 6)
* formfeed: Formatting. (line 131)
* function argument, declaring: Syntactic Conventions.
(line 6)
* function definitions, formatting: Formatting. (line 9)
* function prototypes: Standard C. (line 22)
* getopt: Command-Line Interfaces.
(line 6)
* gettext: Internationalization.
(line 6)
* GNOME: Graphical Interfaces.
(line 17)
* GNOME and Guile: Source Language. (line 24)
* Gnulib: System Functions. (line 37)
* gnustandards project repository: Preface. (line 30)
* gnustandards-commit AT gnu.org mailing list: Preface. (line 24)
* GNUstep: Graphical Interfaces.
(line 6)
* graphical user interface: Graphical Interfaces.
(line 6)
* grave accent: Quote Characters. (line 6)
* GTK+: Graphical Interfaces.
(line 6)
* Guile: Source Language. (line 24)
* implicit int: Syntactic Conventions.
(line 6)
* impossible conditions: Semantics. (line 63)
* installation directories, creating: Directory Variables. (line 20)
* installations, staged: DESTDIR. (line 6)
* interface styles: Graphical Interfaces.
(line 6)
* internationalization: Internationalization.
(line 6)
* keyboard interface: Graphical Interfaces.
(line 17)
* LDAP: OID Allocations. (line 6)
* left quote: Quote Characters. (line 6)
* legal aspects: Legal Issues. (line 6)
* legal papers: Contributions. (line 6)
* length of source lines: Formatting. (line 6)
* libexecdir: Directory Variables. (line 70)
* libiconv: Semantics. (line 11)
* libraries: Libraries. (line 6)
* library functions, and portability: System Functions. (line 6)
* library interface: Graphical Interfaces.
(line 17)
* license for manuals: License for Manuals. (line 6)
* line length: Formatting. (line 6)
* lint: Syntactic Conventions.
(line 17)
* locale-specific quote characters: Quote Characters. (line 6)
* long option names: Option Table. (line 6)
* long-named options: Command-Line Interfaces.
(line 12)
* makefile, conventions for: Makefile Conventions.
(line 6)
* malloc return value: Semantics. (line 22)
* man pages: Man Pages. (line 6)
* manual structure: Manual Structure Details.
(line 6)
* memory allocation failure: Semantics. (line 22)
* memory leak: Memory Usage. (line 23)
* memory usage: Memory Usage. (line 6)
* message text, and internationalization: Internationalization.
(line 29)
* mmap: Mmap. (line 6)
* multiple variables in a line: Syntactic Conventions.
(line 43)
* names of variables, functions, and files: Names. (line 6)
* NEWS file: NEWS File. (line 6)
* non-ASCII characters: Character Set. (line 6)
* non-POSIX systems, and portability: System Portability. (line 32)
* non-standard extensions: Using Extensions. (line 6)
* NUL characters: Semantics. (line 11)
* OID allocations for GNU: OID Allocations. (line 6)
* open brace: Formatting. (line 9)
* opening quote: Quote Characters. (line 6)
* optional features, configure-time: Configuration. (line 98)
* options for compatibility: Compatibility. (line 14)
* options, standard command-line: Command-Line Interfaces.
(line 31)
* output device and program's behavior: User Interfaces. (line 14)
* packaging: Releases. (line 6)
* PATH_INFO, specifying standard options as: Command-Line Interfaces.
(line 31)
* plug-ins: Dynamic Plug-In Interfaces.
(line 6)
* plugin_is_GPL_compatible: Dynamic Plug-In Interfaces.
(line 17)
* portability, and data types: CPU Portability. (line 6)
* portability, and library functions: System Functions. (line 6)
* portability, between system types: System Portability. (line 6)
* POSIX compatibility: Compatibility. (line 6)
* POSIX functions, and portability: System Functions. (line 6)
* POSIXLY_CORRECT, environment variable: Compatibility. (line 21)
* post-installation commands: Install Command Categories.
(line 6)
* pre-installation commands: Install Command Categories.
(line 6)
* prefix: Directory Variables. (line 29)
* program configuration: Configuration. (line 6)
* program design: Design Advice. (line 6)
* program name and its behavior: User Interfaces. (line 6)
* program's canonical name: --version. (line 12)
* programming languages: Source Language. (line 6)
* proprietary programs: Reading Non-Free Code.
(line 6)
* quote characters: Quote Characters. (line 6)
* README file: Releases. (line 21)
* references to non-free material: References. (line 6)
* releasing: Managing Releases. (line 6)
* right quote: Quote Characters. (line 6)
* Savannah repository for gnustandards: Preface. (line 30)
* sbindir: Directory Variables. (line 63)
* signal handling: Semantics. (line 52)
* single quote: Quote Characters. (line 6)
* SNMP: OID Allocations. (line 6)
* spaces before open-paren: Formatting. (line 88)
* staged installs: DESTDIR. (line 6)
* standard command-line options: Command-Line Interfaces.
(line 31)
* standards for makefiles: Makefile Conventions.
(line 6)
* struct types, formatting: Formatting. (line 48)
* syntactic conventions: Syntactic Conventions.
(line 6)
* table of long options: Option Table. (line 6)
* temporary files: Semantics. (line 77)
* temporary variables: Syntactic Conventions.
(line 31)
* texinfo.tex, in a distribution: Releases. (line 78)
* title, change log entry: Change Log Concepts. (line 12)
* TMPDIR environment variable: Semantics. (line 77)
* trademarks: Trademarks. (line 6)
* user interface styles: Graphical Interfaces.
(line 6)
* valgrind: Memory Usage. (line 23)
* version numbers, for releases: Releases. (line 6)
* where to obtain standards.texi: Preface. (line 14)
* X.509: OID Allocations. (line 6)
* xmalloc, in Gnulib: System Functions. (line 44)
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