GNU編碼標準
目錄
*****************
版本
1 關於GNU編碼標準
2 保持自由軟件之自由
2.1 引用私有程序
2.2 接受奉獻
2.3 商標
3 通用程序設計
3.1 使用何種語言
3.2 與其他實現的兼容性
3.3 使用非標準特性
3.4 標準C與準標準C
3.5 條件編譯
4 所有程序的程序行為
4.1 非GNU標準
4.2 編寫健壯的程序
4.3 庫的行為
4.4 格式化錯誤信息
4.5 通用的接口標準
4.6 圖形接口標準
4.7 命令行接口標準
4.7.1 "--version"
4.7.2 "--help"
4.8 長選項列表
4.9 OID的分配
4.10 內存的使用
4.11 文件的使用
5 C的最佳使用
5.1 格式化你的源代碼
5.2 給你的源代碼作注釋
5.3 用純C構建
5.4 給變量、函數和文件命名
5.5 系統類型間的可移植性
5.6 CPU間的可移植性
5.7 調用系統函數
5.8 國際化
5.9 字符集
5.10 引號
5.11 mmap
6 為程序制作文檔
6.1 GNU手冊
6.2 文檔的附加部分與手冊
6.3 手冊結構詳述
6.4 手冊的許可
6.5 手冊的歸屬
6.6 印刷版的手冊
6.7 NEWS文件
6.8 變更記錄
6.8.1 變更記錄的概念
6.8.2 變更記錄的風格
6.8.3 簡單變更
6.8.4 條件變更
6.8.5 指出變更的部分
6.9 手冊頁
6.10 閱讀其他手冊
7 版本的處理
7.1 應該如何配置
7.2 Makefile慣例
7.2.1 Makefile的通用慣例
7.2.2 Makefile的實用程序
7.2.3 指定命令的變量
7.2.4 DESTDIR：支持分階段安裝
7.2.5 用于指定安裝目錄的變量
7.2.6 標準的用戶目標
7.2.7 安裝命令的各類
7.3 制作發行包
8 參考非自由軟件及文檔
附錄 GNU自由文檔許可
索引
版本
*******
GNU編碼標準，最後更新于2009年11月20日
版權（C）：1992、1993、1994、1995、1996、1997、1998、1999、2000、2001、2002、2003、2004、2005、2006、2007、2008、2009自由軟件基金會。
在遵守由自由軟件基金會出版的GNU自由文檔許可協議第1.3版或之後的版本且不改變章節、不帶卷首語及後記的前提下，允許復制、發布和（或）修改此文檔。此許可的副本要包含以"GNU自由文檔許可"為題的章節。
1 關於GNU編碼標準
********************************
GNU編碼標準由Richard Stallman和其他GNU項目志願者撰寫。其宗旨是使GNU系統純正、一致且易于安裝。也可以把此文檔當作編寫可移植的、健壯且可靠的程序的指南。它主要關注C編程，但其中有許多規則和原理亦適用于使用其他語言所進行的程序設計。這些規則通常指出以特定方式編碼的理由。
如果你不是最近直接從GNU項目獲得此文件的話，請檢查有沒有更加新的版本。你可以從GNU的萬維網服務器"http://www.gnu.org/prep/standards/"上獲取多種格式的GNU編碼標準，包括Texinfo源代碼、PDF、HTML、DVI、普通文本等。
如果你正在維護一個官方的GNU軟件包，你除了文檔之外尚需參閱GNU維護者信息（參見目錄：(maintain)Top。譯注：指的是http://www.gnu.org/prep/maintain）。
如果你想獲得這些GNU文檔的每一變更的不同之處，則請通過網絡鏈接"http://lists.gnu.org/mailman/listinfo/gnustandards-commit"加入郵件列表"gnustandards-commit@gnu.org"。在那裡，文檔依然是可用的。
應該把此文檔的校正及你的建議發送到。若你要提建議，則請為此包含一個新的版式以作提示。這是由于我們時間有限。雖然我們喜歡以"standards.texi"或"make-stds.texi"命名文件名且含有上下文差異的文件（譯注：通常用diff程序生成），但是如果你沒有這些文件的話，也請你將建議郵過來。
這些標準所覆蓋的最低要求在編寫GNU軟件包時表現得相當重要。附加標準的需求也很可能會提升。有時，你會建議將這些標準合並到此文檔。如果你認為你的標準通常是有用的，請建議他們這麼幹。
在為你的軟件包設定標準時，你應該避免這裡列出許多問題。最重要的一點是自成一體，亦即堅持你所選擇的慣例，並盡力把它記錄下來。若如此，則對于他人而言，你的程序將會更加容易維護。
GNU Hello項目是一個用于演示如何在遵循GNU編碼標準的前提下編寫普通程序的例子。見"http://www.gnu.org/software/hello/hello.html"。
此GNU編碼標準版本最後更新于2009年11月20日。
2 保持自由軟件之自由
****************************
此章討論你如何才能確保GNU軟件避免法律爭議，以及其他相關爭端。
2.1 引用私有程序
=====================================
任何情況下，你都不要將Unix源代碼或其他私有程序引入到你的GNU項目中。
若你對一個Unix程序的內部組織有著朦朧的記憶，則並不意味著你絕對不能模仿它，但你在模仿時應該在內部將其組織到跟原來的源代碼（譯注："跟原來的源代碼"為譯者根據上下文所補，原文無此語）不同的行。這是由于這很可能使你的結果與Unix版本在細節上有所不同。
譬如：Unix實用程序通常優化為最省內存，若你代之以速度，你的程序將大異。你可以通過將整個輸入文件駐留于內存以供使用來代替使用stdio；使用更加巧妙的算法以表現得比Unix程序更加新；不使用臨時文件；以一遍代替兩遍（我們通過匯代碼來完成）。
或者相反地，強調簡單性，而非速度。對于一些應用程序，以今時今日的計算機速度，使用簡單的算法足以應付。
或者，致力于通用性。譬如：Unix程序通常使用力圖滿足任意限制的靜態表或固定大小的字符串。可通過動態分配來取而代之。確保你的程序能處理輸入文件中的NUL字符及其他特殊字符。
或者，將程序的某部分改寫成獨立可用的庫。或者，使用簡單的垃圾回收器，而非在釋放內存時精確地實施跟蹤。
2.2 接受奉獻
===========================
如果你正在開發的程序的版權為自由軟件基金會所有，則當其他人給你代碼塊並要加入到程序時，我們需要法律文書以使用它－－正如我們請你最初簽署文書時那樣。每個為程序作出重要貢獻的人都必須簽署某些類別的法律文書以便我們擁有明確的所有權；單單主要作者是不夠的。
因此，在接受他人的任何貢獻之前，請告訴我們，以便我們能夠作出安排以獲得文書。然後，在你實際使用這些貢獻之前，請等待至我們告訴你我們已經獲得已簽署的文書為止。
這嘅適用于你發布程序之前，也適用于發布版本之後。如果你收到用于修復缺陷的diff文件，並且它們會導致重大改變的話，我們需要有關此改變的法律文書。
這也適于用注釋及文檔文件。對于版權法而言，注釋和代碼都是文本。版權適用于所有類型的文本。因此，我們需要相應的法律文書。
我們知道請求法律文書是很麻煩的。對于我們而言，又何嘗不是呢？但若你不等待，你將走向孤立無援之境地。譬如：如果貢獻者之雇主不簽署免責聲明，會有什麼後果呢？你將不得不把那些代碼剔除！
你沒必要為零星的幾行修改而去請求法律文書，因為這對于版權保護之目的可謂無傷大雅。同樣，你從建議中所得到的僅僅是一些啟發，而非照搬代碼，則你也無須文書。譬如：若有人給你一個實現，但你以相同的想法寫一個不同的實現，則你亦無須取得文書。
最糟糕的是，若你忘記把其他的貢獻者告訴我們，則來日我們可能會因此而窘迫地出現在法庭上。
對于程序維護者，我們有更多詳細的忠告。若你如今已經在維護一個GNU程序（無論已經發布與否），請向我們要一份副本。你亦可以在線瀏覽"http://www.gnu.org/prep/maintain/"。
2.3 商標
==============
請不要將任何商標確認包含于GNU軟件包或文檔內。
商標確認就是對某種商標的具體描述。GNU項目並不反對基于商標的構思，但這好比叩頭，並沒有法定的要求。因此，我們不使用它。
對他人之商標，要考慮什麼法定要求呢？就是要避免如此使用它們：讀者見我們自己的程序或行為的命名或標識而自然而然地聯想到它們。譬如：因為"Objective C"是（起碼曾經是）一個商標，所以我們必須用"關于Objective C語言的編譯器"來代替"Objective C編譯器"。後者本該是用以表達前者之簡省，但它不能清晰地表達兩者的關系。因此，使用"Objective C"作為一種標識時，容易使人誤解其為一種編譯器，而不是一種語言。
請不要在GNU軟件或文檔內使用"win"來作為微軟Windows的縮寫。套用術語，稱某事物為"win"是一種贊美的形式。如果你自己想謳歌微軟Windows的話，你可以盡你之所能去這樣做，但不要在GNU軟件中這麼幹。通常，我們完整地拼寫"Windows"。但當簡潔性非常重要時（當用于文件名或某些符號名時），我們將其縮寫為"w"。譬如：Emacs處理Windows的文件和函數時，以"w32"打頭。
3 通用程序設計
************************
本章討論一些當你設計程序時應該考慮的問題。
3.1 使用何種語言
==========================
當你要使用一種（譯注：指使用該語言所編寫的源代碼）經編譯後（譯注：指所產生的程序）可高速運行的語言時，C語言是首選。使用其他語言有如使用非標準特性：它會給用戶帶來麻煩。雖然GCC支持其他語言，但用戶會發現必須通過安裝編譯器來使用其他語言構建程序是何等不便。譬如：若你用C++編寫你的程序，用戶必須安裝GNU C++編譯器來編譯你的程序。
C優勝與C++及其他編譯語言的另一點是：更多人認識C，因此，更多人會認為用C編寫的程序易于閱讀和修改。
因此，通常使用C會比其他選擇好得多。
但對于這個結論而言，以下兩種情況是例外的：
* 使用其他語言來編寫一個專給該語言使用的工具是沒問題的。這是因為想構建此工具的人總是已經安裝該語言（譯注：指編譯器）之人。
* 若應用程序只針對一小撮人，則用何種語言書寫程序的問題對他人而言，是無關痛癢的。因此，你可以率性而為。
許多程序被設計得可擴展：它們包含一個比C高級的語言解釋程序。通常很多程序也用這種語言來編寫。Emacs編輯器首先使用此技術。
針對GNU軟件的標準可擴展解釋程序是Guile("http://www.gnu.org/software/guile/")，它實現了Scheme語言（一種特別精簡的Lisp方言）。Guile也包含針對GTK+/GNOME的封裝，使其用Guile編寫現代的GUI功能時顯得很實用。我們不拒絕用其他諸如Perl和Python的腳本語言編寫程序，但使用Guile對于GNU系統的全局一致性而言，是很重要的。
3.2 與其他實現的兼容性
============================================
對于偶然的例外情況，GNU實用程序及庫應該向上兼容于Berkeley Unix中的這些情況；若標準C指定其行為，則同時要向上兼容于標準C；若POSIX中的這些情指定其行為，則同時要向上兼容于POSIX。
當這些標準衝突時，為每種標準提供兼容模式是有益的。
標準C和POSIX禁止很多類型的擴展。無論如何，不妨使用擴展，並通過包含"--ansi"、"--posix"或"--compatible"選項來關閉它們。然而，若擴展有破壞任何實際程序或腳本的重大風險時，實際上未必向上兼容。
若環境變量"POSIXLY_CORRECT"被定義（即使定義為null值），則許多GNU程序禁止與POSIX衝突的擴展。如果合適的話，則請使你的程序可識別這個變量。
當一個特性僅被用戶使用（不被程序或命令文件使用）並且Unix有拙劣的實現時，不妨以某些完全不同且更好的東西來徹底代替它（例如："vi"為Emacs所代替）。但還是提供兼容特性為妙（有自由的"vi"克隆，因此，我們提供它）。
另外，不管有沒有先例，有用的特性是受歡迎的。
3.3 使用非標準特性
===============================
許多現存的GNU工具支持很多比Unix工具更便利的擴展。是否使用這些擴展來實現你的程序是一道難題。
一方面，使用這些擴展可生成更為純淨的程序。另一方面，除非其他GNU工具可用，否則人們將不能構建程序。這可能導致程序運行于更少類型的機器。
有些擴展可以輕易提供兩種選擇。譬如：你可以用關鍵字"INLINE"定義函數，並且將其定義為一個由編譯器決定擴展為"inline"或空的宏。
通常，最好在你可以不使用擴展而能直接實現時不使用它，但使用它能帶來巨大的提升時就使用它。
這個規則中的一個例外是諸如Emacs之類運行于很多種系統的巨大的舊有程序。在這種程序中使用GNU擴展將會使用戶感到不快。因此，我們不這樣做。
另一個例外是用作編譯的一部分的程序：為了引導GNU編譯工具，所有東西都必須用其他編譯器編譯。若其需要GNU編譯器，則沒人能在還沒安裝它們之前就編譯它們。這在某些情況下是極端棘手的。
3.4 標準C與準標準C
=================================
1989標準C現在相當普及。因此，在新程序中使用它的特性是可行的。但有一個例外：不要使用標準C的"trigraph"特性。
1999標準C仍未普及。因此，不要在程序中強求這些特性。若其特性已有實現，則用亦無妨。
然而，在多數程序中，準標準編譯器易于提供。因此，若你知道如何用，則但用無妨。若你所維護的程序支持這些，你應該使其保持正常運轉。
為了支持準標準C，以下用標準原型形式編寫的函數定義：
int
foo (int x, int y)
...
應該用如下的準標準風格來編寫的定義來代替：
int
foo (x, y)
int x, y;
...
並用單獨的聲明來指明參數原型：
int foo (int, int);
無論如何，在一個頭文件中，你需要如此的聲明。在所有含有函數調用的文件中包含原型是有好處的。而且一旦你有所聲明，用準標準風格編寫函數定義對你而言亦無損失。
這種技巧不適用于比"int"窄的整數類型。若你把參數看作比"int"窄的類型，則不如幹脆將其聲明為"int"。
只有幾種特殊情況是難于使用這種技巧的。譬如：若一個函數參數需要隱藏系統類型"dev_t"，你就麻煩了。因為"dev_t"在某些機器上比"int"窄；但你不能用"int"來代替，因為"dev_t"在某些機器上比"int"寬。對于非標準定義，沒有類型可以安全地應用于所有機器。唯一支持非標準C並傳遞如此的參數的方法是用Autoconf檢查"dev_t"的寬度，並選擇相應的參數類型。未必值得這樣去解決問題。
為了支持不支持原型的準標準編譯器，你可能要像如下那樣使用預處理宏：
/* 為一個普通的外部函數聲明原型 */
#if defined (__STDC__) || defined (WINDOWSNT)
#define P_(proto) proto
#else
#define P_(proto) ()
#endif
3.5 條件編譯
===========================
當支持在構建你的程序時已知的配置選項時，相較于條件編譯，我們更喜歡使用"if(...)"。因为对于后一种情况而言，编译器可以更广泛地执行可能的代码路径检验。
譬如，请编写：
if (HAS_FOO)
...
else
...
以代替：
#ifdef HAS_FOO
...
#else
...
#endif
对于两种情况，如GCC般的现代编译器都会精确地生成同样的代码。在若干项目里，我们已经非常成功地运用了类似的技术。当然，前者假定"HAS_FOO"定义为0或1。
这并非是解决可移植性问题的良方，而且并非总是合适。与此相对，以下的这种方略将为GCC开发人员节省数小时每年，甚至数日每年。
在GCC中，像"REVERSIBLE_CC_MODE"这种如函数般的宏不能简单地用于"if(...)语句。这里有一个容易的解决方法。像如下的例子那样，简单地引入另一个宏"HAS_REVERSIBLE_CC_MODE"：
#ifdef REVERSIBLE_CC_MODE
#define HAS_REVERSIBLE_CC_MODE 1
#else
#define HAS_REVERSIBLE_CC_MODE 0
#endif
4 所有程序的程序行為
***********************************
此章描述編寫健壯軟件的慣例。同時，描述有關錯誤消息、命令行接口、庫行為的通用標準。
4.1 非GNU標準
=====================
GNU項目注意到標準被其他組織以建議的形式發行，而非命令。我們考慮這些標準，但不"聽命"于它們。開發GNU程序時，當外部標準規範使GNU系統的總體客觀感覺更好時，你應該執行之。否則，就不該執行了。
在多數情況下，以下的發行標準便于用戶－－這意味著他們的程序或腳本更具移植性。例如：GCC實現了幾乎所有這個標準所指出的標準C的特性。若非如此，C程序開發者將會不滿意。大部分GNU實用程序遵從POSIX.2規範。若我們的程序不兼容，則shell腳本作者和用戶都會不滿意。
但是我們不嚴格遵從任何一個規範，且明確指出我們選擇不遵從哪些，以便使GNU系統對用戶而言更好。
例如：標準C宣稱幾乎所有C擴展都被禁止。真暈！GCC實現了許多擴展，其中一些後來被採用為標準的一部分。若你想按標準"要求"那般給出錯誤信息以期實現這些構想的話，你必須指明"--pedantic"選項。它只被如此實現：足令我們可以說"GCC是標準的一個100％的實現"，而不是因為有任何實際上使用它的理由。
POSIX.2指定"df"和"du"必須默認以512字節為單位來輸出。而用戶想要的是以1k作為單位。因此，這才是我们設置的默認值。若你想得到POSIX所"要求"的可笑行為，你必須設置環境變量"POSIXLY_CORRECT"（最初打算命名為"POSIX_ME_HARDER)。
當GNU實用程序支持長命令行選項名以及混合選項與普通參數時，亦違反POSIX.2的字母規範。在實踐中，這種較小的POSIX不兼容性從來也不算問題，而且很實用。
特別是，不要僅僅因為標準說這是"禁止"或"反對"的而拒絕新特性或刪除舊特性。
4.2 編寫健壯的程序
===========================
避免包括文件名、行、文件和符號在內的任何動態分配的數據結構在長度及數量上受到任何限制。對于多數的Unix實用程序，"長行被安靜地截斷"。這對于GNU實用程序而言，是不可接受的。
實用程序讀文件時不應遺漏NUL字符或任何其他包括編碼值大于0177在內的非打印字符。僅有的實用的例外情況是，特定的實用程序想連接不能處理這些字符的特定類型的終端或打印機。每當可能時，嘗試使程序在諸如UTF-8和其他編碼那表示多字節字符的字節序的情況下正確運行。
Utilities reading files should not drop NUL characters, or any other
nonprinting characters _including those with codes above 0177_. The
only sensible exceptions would be utilities specifically intended for
interface to certain types of terminals or printers that can't handle
those characters. Whenever possible, try to make programs work
properly with sequences of bytes that represent multibyte characters,
using encodings such as UTF-8 and others.
Check every system call for an error return, unless you know you
wish to ignore errors. Include the system error text (from `perror' 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
zero. 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.
In Unix, `realloc' can destroy the storage block if it returns zero.
GNU `realloc' does not have this bug: if it fails, the original block
is unchanged. Feel free to assume the bug is fixed. If you wish to
run your program on Unix, and wish to avoid lossage in this case, you
can use the GNU `malloc'.
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. 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 libiberty.
In bash, use `set -C' to avoid this problem.
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.
4.4 Formatting Error Messages
=============================
Error messages from compilers should look like this:
SOURCE-FILE-NAME:LINENO: MESSAGE
If you want to mention the column number, use one of these formats:
SOURCE-FILE-NAME:LINENO:COLUMN: MESSAGE
SOURCE-FILE-NAME: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.
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:
SOURCE-FILE-NAME:LINENO-1.COLUMN-1-LINENO-2.COLUMN-2: MESSAGE
SOURCE-FILE-NAME:LINENO-1.COLUMN-1-COLUMN-2: MESSAGE
SOURCE-FILE-NAME:LINENO-1-LINENO-2: MESSAGE
When an error is spread over several files, you can use this format:
FILE-1:LINENO-1.COLUMN-1-FILE-2:LINENO-2.COLUMN-2: MESSAGE
Error messages from other noninteractive programs should look like
this:
PROGRAM:SOURCE-FILE-NAME: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:SOURCE-FILE-NAME: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.
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.
Likewise, please don't make the behavior of the program depend on the
type of output device it is used with. 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.
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.
4.6 Standards for Graphical Interfaces
======================================
When you write a program that provides a graphical user interface,
please make it work with X Windows and the GTK+ toolkit unless the
functionality specifically requires some alternative (for example,
"displaying jpeg images while in console mode").
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 CORBA interface (for use from
GNOME), a library interface (for use from C), and perhaps a
keyboard-driven console interface (for use by users from console mode).
Once you are doing the work to provide the functionality and the
graphical interface, these won't be much extra work.
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.
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 abbrevations 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
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 Copyright Notices: (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 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/Guile
GNU GPL with the exception for Guile; for example, GPLv3+/Guile
means the GNU GPL version 3 or later, with the extra exception for
Guile.
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://www.perlfoundation.org/legal'.
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://www.python.org/2.0.1/license.html'.
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'.
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 , and the general page for
help using GNU programs. The format should be like this:
Report bugs to: MAILING-ADDRESS
PKG home page:
General help using GNU software:
It is ok to mention other appropriate mailing lists and web pages.
4.8 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 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'.
4.9 OID Allocations
===================
The OID (object identifier) 1.3.6.1.4.1.11591 has been assigned to the
GNU Project (thanks to Werner Koch). 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
. 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
1.3.6.1.4.1.11591.5 GNU Shishi
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
4.10 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 zero.
4.11 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.
5 Making The Best Use of C
**************************
This chapter provides advice on how best to use the C language when
writing GNU software.
5.1 Formatting Your Source Code
===============================
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)
...
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.
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 the reader can see that for himself.
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 */
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.
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.
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)) == 0)
fatal ("virtual memory exhausted");
instead, write this:
foo = (char *) malloc (sizeof *foo);
if (foo == 0)
fatal ("virtual memory exhausted");
Don't make the program ugly to placate `lint'. Please don't insert
any casts to `void'. Zero without a cast is perfectly fine as a null
pointer constant, except when calling a varargs function.
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.
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.
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);
}
It used to be ok to not worry about the difference between pointers
and integers when passing arguments to functions. However, on most
modern 64-bit machines pointers are wider than `int'. Conversely,
integer types like `long long int' and `off_t' are wider than pointers
on most modern 32-bit machines. Hence it's often better nowadays to
use prototypes to define functions whose argument types are not trivial.
In particular, if functions accept varying argument counts or types
they should be declared using prototypes containing `...' and defined
using `stdarg.h'. For an example of this, please see the Gnulib
(http://www.gnu.org/software/gnulib/) error module, which declares and
defines the following function:
/* Print a message with `fprintf (stderr, FORMAT, ...)';
if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM).
If STATUS is nonzero, terminate the program with `exit (STATUS)'. */
void error (int status, int errnum, const char *format, ...);
A simple way to use the Gnulib error module is to obtain the two
source files `error.c' and `error.h' from the Gnulib library source
code repository at `http://git.savannah.gnu.org/gitweb/?p=gnulib.git'.
Here's a sample use:
#include "error.h"
#include
#include
char *program_name = "myprogram";
FILE *
xfopen (char const *name)
{
FILE *fp = fopen (name, "r");
if (! fp)
error (1, errno, "cannot read %s", name);
return fp;
}
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.
5.7 Calling System Functions
============================
C implementations differ substantially. Standard C reduces but does
not eliminate the incompatibilities; meanwhile, many GNU packages still
support pre-standard compilers because this is not hard to do. This
chapter gives recommendations for how to use the more-or-less standard C
library functions to avoid unnecessary loss of portability.
* Don't use the return value of `sprintf'. It returns the number of
characters written on some systems, but not on all systems.
* Be aware that `vfprintf' is not always available.
* `main' should be declared to return type `int'. It should
terminate either by calling `exit' or by returning the integer
status code; make sure it cannot ever return an undefined value.
* Don't declare system functions explicitly.
Almost any declaration for a system function is wrong on some
system. To minimize conflicts, leave it to the system header
files to declare system functions. If the headers don't declare a
function, let it remain undeclared.
While it may seem unclean to use a function without declaring it,
in practice this works fine for most system library functions on
the systems where this really happens; thus, the disadvantage is
only theoretical. By contrast, actual declarations have
frequently caused actual conflicts.
* If you must declare a system function, don't specify the argument
types. Use an old-style declaration, not a Standard C prototype.
The more you specify about the function, the more likely a
conflict.
* In particular, don't unconditionally declare `malloc' or `realloc'.
Most GNU programs use those functions just once, in functions
conventionally named `xmalloc' and `xrealloc'. These functions
call `malloc' and `realloc', respectively, and check the results.
Because `xmalloc' and `xrealloc' are defined in your program, you
can declare them in other files without any risk of type conflict.
On most systems, `int' is the same length as a pointer; thus, the
calls to `malloc' and `realloc' work fine. For the few
exceptional systems (mostly 64-bit machines), you can use
*conditionalized* declarations of `malloc' and `realloc'--or put
these declarations in configuration files specific to those
systems.
* The string functions require special treatment. Some Unix systems
have a header file `string.h'; others have `strings.h'. Neither
file name is portable. There are two things you can do: use
Autoconf to figure out which file to include, or don't include
either file.
* If you don't include either strings file, you can't get
declarations for the string functions from the header file in the
usual way.
That causes less of a problem than you might think. The newer
standard string functions should be avoided anyway because many
systems still don't support them. The string functions you can
use are these:
strcpy strncpy strcat strncat
strlen strcmp strncmp
strchr strrchr
The copy and concatenate functions work fine without a declaration
as long as you don't use their values. Using their values without
a declaration fails on systems where the width of a pointer
differs from the width of `int', and perhaps in other cases. It
is trivial to avoid using their values, so do that.
The compare functions and `strlen' work fine without a declaration
on most systems, possibly all the ones that GNU software runs on.
You may find it necessary to declare them *conditionally* on a few
systems.
The search functions must be declared to return `char *'. Luckily,
there is no variation in the data type they return. But there is
variation in their names. Some systems give these functions the
names `index' and `rindex'; other systems use the names `strchr'
and `strrchr'. Some systems support both pairs of names, but
neither pair works on all systems.
You should pick a single pair of names and use it throughout your
program. (Nowadays, it is better to choose `strchr' and `strrchr'
for new programs, since those are the standard names.) Declare
both of those names as functions returning `char *'. On systems
which don't support those names, define them as macros in terms of
the other pair. For example, here is what to put at the beginning
of your file (or in a header) if you want to use the names
`strchr' and `strrchr' throughout:
#ifndef HAVE_STRCHR
#define strchr index
#endif
#ifndef HAVE_STRRCHR
#define strrchr rindex
#endif
char *strchr ();
char *strrchr ();
Here we assume that `HAVE_STRCHR' and `HAVE_STRRCHR' are macros
defined in systems where the corresponding functions exist. One way to
get them properly defined is to use Autoconf.
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'..."));
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);
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 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, as one cannot in general mix encodings reliably.
5.10 Quote Characters
=====================
In the C locale, GNU programs should stick to plain ASCII for quotation
characters in messages to users: preferably 0x60 (``') for left quotes
and 0x27 (`'') for right quotes. It is ok, but not required, to use
locale-specific quotes in other locales.
The Gnulib (http://www.gnu.org/software/gnulib/) `quote' and
`quotearg' modules provide a reasonably straightforward way to support
locale-specific quote characters, as well as taking care of other
issues, such as quoting a filename that itself contains a quote
character. See the Gnulib documentation for usage details.
In any case, the documentation for your program should clearly
specify how it does quoting, if different than the preferred method of
``' and `''. This is especially important if the output of your
program is ever likely to be parsed by another program.
Quotation characters are a difficult area in the computing world at
this time: there are no true left or right quote characters in Latin1;
the ``' character we use was standardized there as a grave accent.
Moreover, Latin1 is still not universally usable.
Unicode contains the unambiguous quote characters required, and its
common encoding UTF-8 is upward compatible with Latin1. However,
Unicode and UTF-8 are not universally well-supported, either.
This may change over the next few years, and then we will revisit
this.
5.11 Mmap
=========
Don't assume that `mmap' 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.
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.
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 list all
the functions, variables, options, and important concepts that are part
of the program. One combined Index should do for a short manual, but
sometimes for a complex package it is better to use multiple indices.
The Texinfo manual includes advice on preparing good index entries, see
*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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
There's no need to describe the full purpose of the changes or how
they work together. If you think that a change calls for explanation,
you're probably right. Please do explain it--but please put the
explanation in comments in the code, where people will see it whenever
they see the code. For example, "New function" is enough for the
change log when you add a function, because there should be a comment
before the function definition to explain what it does.
In the past, we recommended not mentioning changes in non-software
files (manuals, help files, etc.) in change logs. However, we've been
advised that it is a good idea to include them, for the sake of
copyright records.
However, sometimes it is useful to write one line to describe the
overall purpose of a batch of changes.
The easiest way to add an entry to `ChangeLog' is with the Emacs
command `M-x add-change-log-entry'. An entry should have an asterisk,
the name of the changed file, and then in parentheses the name of the
changed functions, variables or whatever, followed by a colon. Then
describe the changes you made to that function or variable.
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
* 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. When two
entries represent parts of the same change, so that they work together,
then don't put blank lines between them. Then you can omit the file
name and the asterisk when successive entries are in the same file.
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
* sewing.c: Make it sew.
rather than this:
2002-07-14 Usual Maintainer
* sewing.c: Make it sew. Patch by jdoe@gnu.org.
As for the date, that should be the date you applied the change.
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.
6.8.4 Conditional Changes
-------------------------
C programs often contain compile-time `#if' conditionals. Many changes
are conditional; sometimes you add a new definition which is entirely
contained in a conditional. It is very useful to indicate in the
change log the conditions for which the change applies.
Our convention for indicating conditional changes is to use square
brackets around the name of the condition.
Here is a simple example, describing a change which is conditional
but does not have a function or entity name associated with it:
* xterm.c [SOLARIS2]: Include string.h.
Here is an entry describing a new definition which is entirely
conditional. This new definition for the macro `FRAME_WINDOW_P' is
used only when `HAVE_X_WINDOWS' is defined:
* frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined.
Here is 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.
Here is an entry for a change that takes affect only when a certain
macro is _not_ defined:
(gethostname) [!HAVE_SOCKETS]: Replace with winsock version.
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) : Handle case that
user-specified option string is empty.
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 License Notices for Other Files: (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.
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.
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.
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 --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.
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.
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 -e 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 -e $(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'.
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 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) $(YACC)
When you use `ranlib' or `ldconfig', you should make sure nothing
bad happens if the system does not have the program in question.
Arrange to ignore an error from that command, and print a message before
the command to tell the user that failure of this command does not mean
a problem. (The Autoconf `AC_PROG_RANLIB' macro can help with this.)
If you use symbolic links, you should implement a fallback for
systems that don't have symbolic links.
Additional utilities that can be used via Make variables are:
chgrp chmod chown mknod
It is ok to use other utilities in Makefile portions (or scripts)
intended only for particular systems where you know those utilities
exist.
7.2.3 Variables for Specifying Commands
---------------------------------------
Makefiles should provide variables for overriding certain commands,
options, and so on.
In particular, you should run most utility programs via variables.
Thus, if you use Bison, have a variable named `BISON' whose default
value is set with `BISON = bison', and refer to it with `$(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)
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.
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.
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@'.)
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 `$(datarootdir)/emacs/site-lisp'.
If you are using Autoconf, write the default as `@lispdir@'. In
order to make `@lispdir@' work, you need the following lines in
your `configure.in' file:
lispdir='${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.
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. Users who don't
mind being helpless can strip the executables later if they wish.
`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. Devil-may-care
users can use 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:
$(DESTDIR)$(infodir)/foo.info: foo.info
$(POST_INSTALL)
# There may be a newer info file in . than in srcdir.
-if test -f foo.info; then d=.; \
else d=$(srcdir); fi; \
$(INSTALL_DATA) $$d/foo.info $(DESTDIR)$@; \
# Run install-info only if it exists.
# Use `if' instead of just prepending `-' to the
# line so we notice real errors from install-info.
# We use `$(SHELL) -c' because some shells do not
# fail gracefully when there is an unknown command.
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.(1) Alternatively, write just 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) $(srcdir)/foo.texi
Again, you would define the variable `TEXI2HTML' in the Makefile;
for example, it might run `makeinfo --no-split --html' (`makeinfo'
is part of the Texinfo distribution).
`dist'
Create a distribution tar file for this program. The tar file
should be set up so that the file names in the tar file start with
a subdirectory name which is the name of the package it is a
distribution for. This name can include the version number.
For example, the distribution tar file of GCC version 1.40 unpacks
into a subdirectory named `gcc-1.40'.
The easiest way to do this is to create a subdirectory
appropriately named, use `ln' or `cp' to install the proper files
in it, and then `tar' that subdirectory.
Compress the tar file with `gzip'. For example, the actual
distribution file for GCC version 1.40 is called `gcc-1.40.tar.gz'.
It is ok to support other free compression formats as well, such as
`bzip2' and `lzma'.
The `dist' target should explicitly depend on all non-source files
that are in the distribution, to make sure they are up to date in
the distribution. *Note Making Releases: Releases.
`check'
Perform self-tests (if any). The user must build the program
before running the tests, but need not install the program; you
should write the self-tests so that they work when the program is
built but not installed.
The following targets are suggested as conventional names, for
programs in which they are useful.
`installcheck'
Perform installation tests (if any). The user must build and
install the program before running the tests. You should not
assume that `$(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 Texinfo 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',
# 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.
---------- Footnotes ----------
(1) `texi2dvi' uses TeX to do the real work of formatting. TeX is
not distributed with Texinfo.
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}
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' which gives
the name of the package, and a general description of what it does. It
is also good to explain the purpose of each of the first-level
subdirectories in the package, if there are any. The `README' file
should either state the version number of the package, or refer to where
in the package it can be found.
The `README' file should refer to the file `INSTALL', which should
contain an explanation of the installation procedure.
The `README' file should also refer 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, provided they are
up-to-date and machine-independent, so that building the distribution
normally will never modify them. We commonly include non-source files
produced by Bison, `lex', TeX, and `makeinfo'; this helps avoid
unnecessary dependencies between our distributions, so that users can
install whichever packages they want to install.
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 the directory into which the distribution unpacks (as
well as any subdirectories) are all world-writable (octal mode 777).
This is so that old versions of `tar' which preserve the ownership and
permissions of the files from the tar archive will be able to extract
all the files even if the user is unprivileged.
Make sure that all the files in the distribution are world-readable.
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.
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 . 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 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 (or
mention by name) web sites that contain such material. This policy is
relevant particularly for the web pages for a GNU package.
Following links from nearly any web site can lead eventually to
non-free software; this is inherent in the nature of the web. So it
makes no sense to criticize a site for having such links. As long as
the site does not itself recommend a non-free program, there is no need
to consider the question of the sites that it links to for other
reasons.
Thus, for example, you should not refer to AT&T's web site if that
recommends AT&T's non-free software packages; you should not refer to a
site that links to AT&T's site presenting it as a place to get some
non-free program, because that link recommends and legitimizes the
non-free program. However, that a site contains a link to AT&T's web
site for some other purpose (such as long-distance telephone service)
is not an objection against it.
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.
Index
*****
#endif, commenting: See 5.2. (line 2319)
--help output: See 4.7.2. (line 948)
--version output: See 4.7.1. (line 798)
-Wall compiler option: See 5.3. (line 2352)
accepting contributions: See 2.2. (line 185)
address for bug reports: See 4.7.2. (line 953)
ANSI C standard: See 3.4. (line 374)
arbitrary limits on data: See 4.2. (line 529)
ASCII characters: See 5.9. (line 2862)
autoconf: See 5.5. (line 2521)
avoiding proprietary code: See 2.1. (line 151)
behavior, dependent on program's name: See 4.5. (line 714)
binary packages: See 7.2.7. (line 4547)
bindir: See 7.2.5. (line 3895)
braces, in C source: See 5.1. (line 2145)
bug reports: See 4.7.2. (line 953)
canonical name of a program: See 4.7.1. (line 804)
casting pointers to integers: See 5.6. (line 2643)
CGI programs, standard options for: See 4.7. (line 789)
change logs: See 6.8. (line 3148)
change logs, conditional changes: See 6.8.4. (line 3292)
change logs, style: See 6.8.2. (line 3199)
character set: See 5.9. (line 2862)
command-line arguments, decoding: See 4.2. (line 569)
command-line interface: See 4.7. (line 764)
commenting: See 5.2. (line 2265)
compatibility with C and POSIX standards: See 3.2. (line 309)
compiler warnings: See 5.3. (line 2352)
conditional changes, and change logs: See 6.8.4. (line 3292)
conditionals, comments for: See 5.2. (line 2319)
configure: See 7.1. (line 3407)
control-L: See 5.1. (line 2257)
conventions for makefiles: See 7.2. (line 3588)
corba: See 4.6. (line 755)
credits for manuals: See 6.5. (line 3113)
data types, and portability: See 5.6. (line 2560)
declaration for system functions: See 5.7. (line 2670)
DESTDIR: See 7.2.4. (line 3801)
documentation: See 6. (line 2924)
doschk: See 5.4. (line 2490)
downloading this manual: See 1. (line 101)
encodings: See 5.9. (line 2862)
error messages: See 4.2. (line 542)
error messages, formatting: See 4.4. (line 652)
exec_prefix: See 7.2.5. (line 3877)
expressions, splitting: See 5.1. (line 2220)
FDL, GNU Free Documentation License: See Appendix A.
(line 4756)
file usage: See 4.11. (line 2123)
file-name limitations: See 5.4. (line 2490)
formatting error messages: See 4.4. (line 652)
formatting source code: See 5.1. (line 2145)
formfeed: See 5.1. (line 2257)
function argument, declaring: See 5.3. (line 2348)
function prototypes: See 3.4. (line 385)
getopt: See 4.7. (line 764)
gettext: See 5.8. (line 2767)
gnome: See 4.6. (line 755)
GNOME and Guile: See 3.1. (line 298)
gnustandards-commit@gnu.org mailing list: See 1. (line 111)
graphical user interface: See 4.6. (line 745)
grave accent: See 5.10. (line 2877)
gtk+: See 4.6. (line 745)
Guile: See 3.1. (line 298)
implicit int: See 5.3. (line 2348)
impossible conditions: See 4.2. (line 593)
installations, staged: See 7.2.4. (line 3801)
internationalization: See 5.8. (line 2767)
LDAP: See 4.9. (line 2055)
left quote: See 5.10. (line 2877)
legal aspects: See 2. (line 145)
legal papers: See 2.2. (line 185)
libexecdir: See 7.2.5. (line 3908)
libraries: See 4.3. (line 624)
library functions, and portability: See 5.7. (line 2655)
license for manuals: See 6.4. (line 3094)
lint: See 5.3. (line 2451)
locale-specific quote characters: See 5.10. (line 2877)
long option names: See 4.8. (line 967)
long-named options: See 4.7. (line 770)
makefile, conventions for: See 7.2. (line 3588)
malloc return value: See 4.2. (line 548)
man pages: See 6.9. (line 3336)
manual structure: See 6.3. (line 3067)
memory allocation failure: See 4.2. (line 548)
memory usage: See 4.10. (line 2103)
message text, and internationalization: See 5.8. (line 2790)
mmap: See 5.11. (line 2908)
multiple variables in a line: See 5.3. (line 2377)
names of variables, functions, and files: See 5.4. (line 2458)
NEWS file: See 6.7. (line 3134)
non-ASCII characters: See 5.9. (line 2862)
non-POSIX systems, and portability: See 5.5. (line 2530)
non-standard extensions: See 3.3. (line 341)
NUL characters: See 4.2. (line 534)
OID allocations for GNU: See 4.9. (line 2055)
open brace: See 5.1. (line 2145)
optional features, configure-time: See 7.1. (line 3501)
options for compatibility: See 3.2. (line 317)
options, standard command-line: See 4.7. (line 789)
output device and program's behavior: See 4.5. (line 721)
packaging: See 7.3. (line 4574)
PATH_INFO, specifying standard options as: See 4.7. (line 789)
portability, and data types: See 5.6. (line 2560)
portability, and library functions: See 5.7. (line 2655)
portability, between system types: See 5.5. (line 2504)
POSIX compatibility: See 3.2. (line 309)
POSIXLY_CORRECT, environment variable: See 3.2. (line 324)
post-installation commands: See 7.2.7. (line 4473)
pre-installation commands: See 7.2.7. (line 4473)
prefix: See 7.2.5. (line 3867)
program configuration: See 7.1. (line 3407)
program design: See 3. (line 260)
program name and its behavior: See 4.5. (line 714)
program's canonical name: See 4.7.1. (line 804)
programming languages: See 3.1. (line 266)
proprietary programs: See 2.1. (line 151)
quote characters: See 5.10. (line 2877)
README file: See 7.3. (line 4589)
references to non-free material: See 8. (line 4650)
releasing: See 7. (line 3396)
sbindir: See 7.2.5. (line 3901)
signal handling: See 4.2. (line 582)
SNMP: See 4.9. (line 2055)
spaces before open-paren: See 5.1. (line 2214)
staged installs: See 7.2.4. (line 3801)
standard command-line options: See 4.7. (line 789)
standards for makefiles: See 7.2. (line 3588)
string library functions: See 5.7. (line 2704)
syntactic conventions: See 5.3. (line 2348)
table of long options: See 4.8. (line 967)
temporary files: See 4.2. (line 607)
temporary variables: See 5.3. (line 2365)
texinfo.tex, in a distribution: See 7.3. (line 4638)
TMPDIR environment variable: See 4.2. (line 607)
trademarks: See 2.3. (line 230)
where to obtain standards.texi: See 1. (line 101)
X.509: See 4.9. (line 2055)
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