9 Using History Interactively

This chapter describes how to use the gnu History Library interactively, from a user's standpoint. It should be considered a user's guide. For information on using the gnu History Library in other programs, see the gnu Readline Library Manual.

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9.1 Bash History Facilities

When the -o history option to the set builtin is enabled (see The Set Builtin), the shell provides access to the command history, the list of commands previously typed. The value of the HISTSIZE shell variable is used as the number of commands to save in a history list. The text of the last $HISTSIZE commands (default 500) is saved. The shell stores each command in the history list prior to parameter and variable expansion but after history expansion is performed, subject to the values of the shell variables HISTIGNORE and HISTCONTROL.

When the shell starts up, the history is initialized from the file named by the HISTFILE variable (default ~/.bash_history). The file named by the value of HISTFILE is truncated, if necessary, to contain no more than the number of lines specified by the value of the HISTFILESIZE variable. When an interactive shell exits, the last $HISTSIZE lines are copied from the history list to the file named by $HISTFILE. If the histappend shell option is set (see Bash Builtins), the lines are appended to the history file, otherwise the history file is overwritten. If HISTFILE is unset, or if the history file is unwritable, the history is not saved. After saving the history, the history file is truncated to contain no more than $HISTFILESIZE lines. If HISTFILESIZE is not set, no truncation is performed.

If the HISTTIMEFORMAT is set, the time stamp information associated with each history entry is written to the history file.

The builtin command fc may be used to list or edit and re-execute a portion of the history list. The history builtin may be used to display or modify the history list and manipulate the history file. When using command-line editing, search commands are available in each editing mode that provide access to the history list (see Commands For History).

The shell allows control over which commands are saved on the history list. The HISTCONTROL and HISTIGNORE variables may be set to cause the shell to save only a subset of the commands entered. The cmdhist shell option, if enabled, causes the shell to attempt to save each line of a multi-line command in the same history entry, adding semicolons where necessary to preserve syntactic correctness. The lithist shell option causes the shell to save the command with embedded newlines instead of semicolons. The shopt builtin is used to set these options. See Bash Builtins, for a description of shopt.

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9.2 Bash History Builtins

fc
          fc [-e ename] [-nlr] [first] [last]
          fc -s [pat=rep] [command]

Fix Command. In the first form, a range of commands from first to last is selected from the history list. Both first and last may be specified as a string (to locate the most recent command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). If last is not specified it is set to first. If first is not specified it is set to the previous command for editing and −16 for listing. If the -l flag is given, the commands are listed on standard output. The -n flag suppresses the command numbers when listing. The -r flag reverses the order of the listing. Otherwise, the editor given by ename is invoked on a file containing those commands. If ename is not given, the value of the following variable expansion is used: ${FCEDIT:-${EDITOR:-vi}}. This says to use the value of the FCEDIT variable if set, or the value of the EDITOR variable if that is set, or vi if neither is set. When editing is complete, the edited commands are echoed and executed.

In the second form, command is re-executed after each instance of pat in the selected command is replaced by rep.

A useful alias to use with the fc command is r='fc -s', so that typing ‘r cc’ runs the last command beginning with cc and typing ‘r’ re-executes the last command (see Aliases).

history
          history [n]
          history -c
          history -d offset
          history [-anrw] [filename]
          history -ps arg

With no options, display the history list with line numbers. Lines prefixed with a ‘*’ have been modified. An argument of n lists only the last n lines. If the shell variable HISTTIMEFORMAT is set and not null, it is used as a format string for strftime to display the time stamp associated with each displayed history entry. No intervening blank is printed between the formatted time stamp and the history line.

Options, if supplied, have the following meanings:

-c
Clear the history list. This may be combined with the other options to replace the history list completely.
-d offset
Delete the history entry at position offset. offset should be specified as it appears when the history is displayed.
-a
Append the new history lines (history lines entered since the beginning of the current Bash session) to the history file.
-n
Append the history lines not already read from the history file to the current history list. These are lines appended to the history file since the beginning of the current Bash session.
-r
Read the current history file and append its contents to the history list.
-w
Write out the current history to the history file.
-p
Perform history substitution on the args and display the result on the standard output, without storing the results in the history list.
-s
The args are added to the end of the history list as a single entry.

When any of the -w, -r, -a, or -n options is used, if filename is given, then it is used as the history file. If not, then the value of the HISTFILE variable is used.

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9.3 History Expansion

The History library provides a history expansion feature that is similar to the history expansion provided by csh. This section describes the syntax used to manipulate the history information.

History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current input line, or fix errors in previous commands quickly.

History expansion takes place in two parts. The first is to determine which line from the history list should be used during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is called the event, and the portions of that line that are acted upon are called words. Various modifiers are available to manipulate the selected words. The line is broken into words in the same fashion that Bash does, so that several words surrounded by quotes are considered one word. History expansions are introduced by the appearance of the history expansion character, which is ‘!’ by default. Only ‘\’ and ‘'’ may be used to escape the history expansion character.

Several shell options settable with the shopt builtin (see Bash Builtins) may be used to tailor the behavior of history expansion. If the histverify shell option is enabled, and Readline is being used, history substitutions are not immediately passed to the shell parser. Instead, the expanded line is reloaded into the Readline editing buffer for further modification. If Readline is being used, and the histreedit shell option is enabled, a failed history expansion will be reloaded into the Readline editing buffer for correction. The -p option to the history builtin command may be used to see what a history expansion will do before using it. The -s option to the history builtin may be used to add commands to the end of the history list without actually executing them, so that they are available for subsequent recall. This is most useful in conjunction with Readline.

The shell allows control of the various characters used by the history expansion mechanism with the histchars variable.

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9.3.1 Event Designators

An event designator is a reference to a command line entry in the history list.

!
Start a history substitution, except when followed by a space, tab, the end of the line, ‘=’ or ‘(’ (when the extglob shell option is enabled using the shopt builtin).
!n
Refer to command line n.
!-n
Refer to the command n lines back.
!!
Refer to the previous command. This is a synonym for ‘!-1’.
!string
Refer to the most recent command starting with string.
!?string[?]
Refer to the most recent command containing string. The trailing ‘?’ may be omitted if the string is followed immediately by a newline.
^string1^string2^
Quick Substitution. Repeat the last command, replacing string1 with string2. Equivalent to !!:s/string1/string2/.
!#
The entire command line typed so far.

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9.3.2 Word Designators

Word designators are used to select desired words from the event. A ‘:’ separates the event specification from the word designator. It may be omitted if the word designator begins with a ‘^’, ‘$’, ‘*’, ‘-’, or ‘%’. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.

For example,

!!
designates the preceding command. When you type this, the preceding command is repeated in toto.
!!:$
designates the last argument of the preceding command. This may be shortened to !$.
!fi:2
designates the second argument of the most recent command starting with the letters fi.

Here are the word designators:

0 (zero)
The 0th word. For many applications, this is the command word.
n
The nth word.
^
The first argument; that is, word 1.
$
The last argument.
%
The word matched by the most recent ‘?string?’ search.
x-y
A range of words; ‘-y’ abbreviates ‘0-y’.
*
All of the words, except the 0th. This is a synonym for ‘1-$’. It is not an error to use ‘*’ if there is just one word in the event; the empty string is returned in that case.
x*
Abbreviates ‘x-$’
x-
Abbreviates ‘x-$’ like ‘x*’, but omits the last word.

If a word designator is supplied without an event specification, the previous command is used as the event.

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9.3.3 Modifiers

After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a ‘:’.

h
Remove a trailing pathname component, leaving only the head.
t
Remove all leading pathname components, leaving the tail.
r
Remove a trailing suffix of the form ‘.suffix’, leaving the basename.
e
Remove all but the trailing suffix.
p
Print the new command but do not execute it.
q
Quote the substituted words, escaping further substitutions.
x
Quote the substituted words as with ‘q’, but break into words at spaces, tabs, and newlines.
s/old/new/
Substitute new for the first occurrence of old in the event line. Any delimiter may be used in place of ‘/’. The delimiter may be quoted in old and new with a single backslash. If ‘&’ appears in new, it is replaced by old. A single backslash will quote the ‘&’. The final delimiter is optional if it is the last character on the input line.
&
Repeat the previous substitution.
g
a
Cause changes to be applied over the entire event line. Used in conjunction with ‘s’, as in gs/old/new/, or with ‘&’.
G
Apply the following ‘s’ modifier once to each word in the event.

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10 Installing Bash

This chapter provides basic instructions for installing Bash on the various supported platforms. The distribution supports the gnu operating systems, nearly every version of Unix, and several non-Unix systems such as BeOS and Interix. Other independent ports exist for ms-dos, os/2, and Windows platforms.

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10.1 Basic Installation

These are installation instructions for Bash.

The simplest way to compile Bash is:

  1. cd to the directory containing the source code and type ‘./configure’ to configure Bash for your system. If you're using csh on an old version of System V, you might need to type ‘sh ./configure’ instead to prevent csh from trying to execute configure itself.

    Running configure takes some time. While running, it prints messages telling which features it is checking for.

  2. Type ‘make’ to compile Bash and build the bashbug bug reporting script.
  3. Optionally, type ‘make tests’ to run the Bash test suite.
  4. Type ‘make install’ to install bash and bashbug. This will also install the manual pages and Info file.

The configure shell script attempts to guess correct values for various system-dependent variables used during compilation. It uses those values to create a Makefile in each directory of the package (the top directory, the builtins, doc, and support directories, each directory under lib, and several others). It also creates a config.h file containing system-dependent definitions. Finally, it creates a shell script named config.status that you can run in the future to recreate the current configuration, a file config.cache that saves the results of its tests to speed up reconfiguring, and a file config.log containing compiler output (useful mainly for debugging configure). If at some point config.cache contains results you don't want to keep, you may remove or edit it.

To find out more about the options and arguments that the configure script understands, type 

     bash-2.04$ ./configure --help

at the Bash prompt in your Bash source directory.

If you need to do unusual things to compile Bash, please try to figure out how configure could check whether or not to do them, and mail diffs or instructions to bash-maintainers@gnu.org so they can be considered for the next release.

The file configure.in is used to create configure by a program called Autoconf. You only need configure.in if you want to change it or regenerate configure using a newer version of Autoconf. If you do this, make sure you are using Autoconf version 2.50 or newer.

You can remove the program binaries and object files from the source code directory by typing ‘make clean’. To also remove the files that configure created (so you can compile Bash for a different kind of computer), type ‘make distclean’.

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10.2 Compilers and Options

Some systems require unusual options for compilation or linking that the configure script does not know about. You can give configure initial values for variables by setting them in the environment. Using a Bourne-compatible shell, you can do that on the command line like this: 

     CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure

On systems that have the env program, you can do it like this: 

     env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure

The configuration process uses GCC to build Bash if it is available.

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10.3 Compiling For Multiple Architectures

You can compile Bash for more than one kind of computer at the same time, by placing the object files for each architecture in their own directory. To do this, you must use a version of make that supports the VPATH variable, such as GNU make. cd to the directory where you want the object files and executables to go and run the configure script from the source directory. You may need to supply the --srcdir=PATH argument to tell configure where the source files are. configure automatically checks for the source code in the directory that configure is in and in `..'.

If you have to use a make that does not supports the VPATH variable, you can compile Bash for one architecture at a time in the source code directory. After you have installed Bash for one architecture, use ‘make distclean’ before reconfiguring for another architecture.

Alternatively, if your system supports symbolic links, you can use the support/mkclone script to create a build tree which has symbolic links back to each file in the source directory. Here's an example that creates a build directory in the current directory from a source directory /usr/gnu/src/bash-2.0: 

     bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .

The mkclone script requires Bash, so you must have already built Bash for at least one architecture before you can create build directories for other architectures.

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10.4 Installation Names

By default, ‘make install’ will install into /usr/local/bin, /usr/local/man, etc. You can specify an installation prefix other than /usr/local by giving configure the option --prefix=PATH, or by specifying a value for the DESTDIR ‘make’ variable when running ‘make install’.

You can specify separate installation prefixes for architecture-specific files and architecture-independent files. If you give configure the option --exec-prefix=PATH, ‘make install’ will use PATH as the prefix for installing programs and libraries. Documentation and other data files will still use the regular prefix.

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10.5 Specifying the System Type

There may be some features configure can not figure out automatically, but need to determine by the type of host Bash will run on. Usually configure can figure that out, but if it prints a message saying it can not guess the host type, give it the --host=TYPE option. ‘TYPE’ can either be a short name for the system type, such as ‘sun4’, or a canonical name with three fields: ‘CPU-COMPANY-SYSTEM’ (e.g., ‘i386-unknown-freebsd4.2’).

See the file support/config.sub for the possible values of each field.

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10.6 Sharing Defaults

If you want to set default values for configure scripts to share, you can create a site shell script called config.site that gives default values for variables like CC, cache_file, and prefix. configure looks for PREFIX/share/config.site if it exists, then PREFIX/etc/config.site if it exists. Or, you can set the CONFIG_SITE environment variable to the location of the site script. A warning: the Bash configure looks for a site script, but not all configure scripts do.

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10.7 Operation Controls

configure recognizes the following options to control how it operates.

--cache-file=file
Use and save the results of the tests in file instead of ./config.cache. Set file to /dev/null to disable caching, for debugging configure.
--help
Print a summary of the options to configure, and exit.
--quiet
--silent
-q
Do not print messages saying which checks are being made.
--srcdir=dir
Look for the Bash source code in directory dir. Usually configure can determine that directory automatically.
--version
Print the version of Autoconf used to generate the configure script, and exit.

configure also accepts some other, not widely used, boilerplate options. ‘configure --help’ prints the complete list.

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10.8 Optional Features

The Bash configure has a number of --enable-feature options, where feature indicates an optional part of Bash. There are also several --with-package options, where package is something like ‘bash-malloc’ or ‘purify’. To turn off the default use of a package, use --without-package. To configure Bash without a feature that is enabled by default, use --disable-feature.

Here is a complete list of the --enable- and --with- options that the Bash configure recognizes.

--with-afs
Define if you are using the Andrew File System from Transarc.
--with-bash-malloc
Use the Bash version of malloc in the directory lib/malloc. This is not the same malloc that appears in gnu libc, but an older version originally derived from the 4.2 bsd malloc. This malloc is very fast, but wastes some space on each allocation. This option is enabled by default. The NOTES file contains a list of systems for which this should be turned off, and configure disables this option automatically for a number of systems.
--with-curses
Use the curses library instead of the termcap library. This should be supplied if your system has an inadequate or incomplete termcap database.
--with-gnu-malloc
A synonym for --with-bash-malloc.
--with-installed-readline[=PREFIX]
Define this to make Bash link with a locally-installed version of Readline rather than the version in lib/readline. This works only with Readline 5.0 and later versions. If PREFIX is yes or not supplied, configure uses the values of the make variables includedir and libdir, which are subdirectories of prefix by default, to find the installed version of Readline if it is not in the standard system include and library directories. If PREFIX is no, Bash links with the version in lib/readline. If PREFIX is set to any other value, configure treats it as a directory pathname and looks for the installed version of Readline in subdirectories of that directory (include files in PREFIX/include and the library in PREFIX/lib).
--with-purify
Define this to use the Purify memory allocation checker from Rational Software.
--enable-minimal-config
This produces a shell with minimal features, close to the historical Bourne shell.

There are several --enable- options that alter how Bash is compiled and linked, rather than changing run-time features.

--enable-largefile
Enable support for large files if the operating system requires special compiler options to build programs which can access large files. This is enabled by default, if the operating system provides large file support.
--enable-profiling
This builds a Bash binary that produces profiling information to be processed by gprof each time it is executed.
--enable-static-link
This causes Bash to be linked statically, if gcc is being used. This could be used to build a version to use as root's shell.

The ‘minimal-config’ option can be used to disable all of the following options, but it is processed first, so individual options may be enabled using ‘enable-feature’.

All of the following options except for ‘disabled-builtins’ and ‘xpg-echo-default’ are enabled by default, unless the operating system does not provide the necessary support.

--enable-alias
Allow alias expansion and include the alias and unalias builtins (see Aliases).
--enable-arith-for-command
Include support for the alternate form of the for command that behaves like the C language for statement (see Looping Constructs).
--enable-array-variables
Include support for one-dimensional array shell variables (see Arrays).
--enable-bang-history
Include support for csh-like history substitution (see History Interaction).
--enable-brace-expansion
Include csh-like brace expansion ( b{a,b}c ==> bac bbc ). See Brace Expansion, for a complete description.
--enable-command-timing
Include support for recognizing time as a reserved word and for displaying timing statistics for the pipeline following time (see Pipelines). This allows pipelines as well as shell builtins and functions to be timed.
--enable-cond-command
Include support for the [[ conditional command. (see Conditional Constructs).
--enable-cond-regexp
Include support for matching POSIX regular expressions using the ‘=~’ binary operator in the [[ conditional command. (see Conditional Constructs).
--enable-debugger
Include support for the bash debugger (distributed separately).
--enable-directory-stack
Include support for a csh-like directory stack and the pushd, popd, and dirs builtins (see The Directory Stack).
--enable-disabled-builtins
Allow builtin commands to be invoked via ‘builtin xxx’ even after xxx has been disabled using ‘enable -n xxx’. See Bash Builtins, for details of the builtin and enable builtin commands.
--enable-dparen-arithmetic
Include support for the ((...)) command (see Conditional Constructs).
--enable-extended-glob
Include support for the extended pattern matching features described above under Pattern Matching.
--enable-help-builtin
Include the help builtin, which displays help on shell builtins and variables (see Bash Builtins).
--enable-history
Include command history and the fc and history builtin commands (see Bash History Facilities).
--enable-job-control
This enables the job control features (see Job Control), if the operating system supports them.
--enable-multibyte
This enables support for multibyte characters if the operating system provides the necessary support.
--enable-net-redirections
This enables the special handling of filenames of the form /dev/tcp/host/port and /dev/udp/host/port when used in redirections (see Redirections).
--enable-process-substitution
This enables process substitution (see Process Substitution) if the operating system provides the necessary support.
--enable-progcomp
Enable the programmable completion facilities (see Programmable Completion). If Readline is not enabled, this option has no effect.
--enable-prompt-string-decoding
Turn on the interpretation of a number of backslash-escaped characters in the $PS1, $PS2, $PS3, and $PS4 prompt strings. See Printing a Prompt, for a complete list of prompt string escape sequences.
--enable-readline
Include support for command-line editing and history with the Bash version of the Readline library (see Command Line Editing).
--enable-restricted
Include support for a restricted shell. If this is enabled, Bash, when called as rbash, enters a restricted mode. See The Restricted Shell, for a description of restricted mode.
--enable-select
Include the select builtin, which allows the generation of simple menus (see Conditional Constructs).
--enable-separate-helpfiles
Use external files for the documentation displayed by the help builtin instead of storing the text internally.
--enable-single-help-strings
Store the text displayed by the help builtin as a single string for each help topic. This aids in translating the text to different languages. You may need to disable this if your compiler cannot handle very long string literals.
--enable-strict-posix-default
Make Bash posix-conformant by default (see Bash POSIX Mode).
--enable-usg-echo-default
A synonym for --enable-xpg-echo-default.
--enable-xpg-echo-default
Make the echo builtin expand backslash-escaped characters by default, without requiring the -e option. This sets the default value of the xpg_echo shell option to on, which makes the Bash echo behave more like the version specified in the Single Unix Specification, version 3. See Bash Builtins, for a description of the escape sequences that echo recognizes.

The file config-top.h contains C Preprocessor ‘#define’ statements for options which are not settable from configure. Some of these are not meant to be changed; beware of the consequences if you do. Read the comments associated with each definition for more information about its effect.

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Appendix A Reporting Bugs

Please report all bugs you find in Bash. But first, you should make sure that it really is a bug, and that it appears in the latest version of Bash. The latest version of Bash is always available for FTP from ftp://ftp.gnu.org/pub/bash/.

Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to bug-bash@gnu.org or posted to the Usenet newsgroup gnu.bash.bug.

All bug reports should include:

bashbug inserts the first three items automatically into the template it provides for filing a bug report.

Please send all reports concerning this manual to chet@po.CWRU.Edu.

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Appendix B Major Differences From The Bourne Shell

Bash implements essentially the same grammar, parameter and variable expansion, redirection, and quoting as the Bourne Shell. Bash uses the posix standard as the specification of how these features are to be implemented. There are some differences between the traditional Bourne shell and Bash; this section quickly details the differences of significance. A number of these differences are explained in greater depth in previous sections. This section uses the version of sh included in SVR4.2 (the last version of the historical Bourne shell) as the baseline reference.

More features unique to Bash may be found in Bash Features.

B.1 Implementation Differences From The SVR4.2 Shell

Since Bash is a completely new implementation, it does not suffer from many of the limitations of the SVR4.2 shell. For instance:

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Appendix C Copying This Manual

Up: Copying This Manual

C.1 GNU Free Documentation License

Version 1.2, November 2002
     Copyright © 2000,2001,2002 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307, USA
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.
  1. 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.

  2. 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.

    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.

  3. 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.

  4. 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.

  5. 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:

    1. 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.
    2. 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.
    3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
    4. Preserve all the copyright notices of the Document.
    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
    6. 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.
    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
    8. Include an unaltered copy of this License.
    9. 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.
    10. 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.
    11. 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.
    12. 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.
    13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
    14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
    15. 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.

  6. 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.”

  7. 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.

  8. 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 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.

  9. 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.

  10. TERMINATION

    You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

  11. 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.

C.1.1 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 1.2
       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.

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