stow/doc/stow.texi

\input texinfo @c -*- texinfo -*-
@c %**start of header
@setfilename stow.info
@settitle Stow
@finalout
@c @smallbook
@c @setchapternewpage odd
@c @footnotestyle separate
@c %**end of header

@include version.texi

@ifinfo
@end ifinfo

@copying
This manual describes GNU Stow version @value{VERSION}
(@value{UPDATED}), a program for managing farms of symbolic links.

Software and documentation is copyrighted by the following:

@copyright{} 1993, 1994, 1995, 1996 Bob Glickstein @email{bobg+stow@@zanshin.com}
@*
@copyright{} 2000, 2001 Guillaume Morin @email{gmorin@@gnu.org}
@*
@copyright{} 2007 Kahlil (Kal) Hodgson @email{kahlil@@internode.on.net}
@*
@copyright{} 2011 Adam Spiers @email{stow@@adamspiers.org}

@quotation
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries a copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).
@end ignore

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
section entitled ``GNU General Public License'' is included with the
modified manual, and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to this
one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation
approved by the Free Software Foundation.
@end quotation
@end copying

@dircategory System administration
@direntry
* Stow: (stow).           GNU Stow.
@end direntry

@c ===========================================================================
@titlepage
@title Stow @value{VERSION}
@subtitle Managing the installation of software packages
@author Bob Glickstein, Zanshin Software, Inc.
@author Kahlil Hodgson, RMIT University, Australia.
@author Guillaume Morin
@author Adam Spiers
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@c FIXME: How to include the TOC in the TOC?
@c @node Table of Contents, Top, (dir), (dir)
@c @unnumbered Table of Contents
@contents

@c ==========================================================================
@ifnottex
@node Top
@top

This manual describes GNU Stow @value{VERSION} (@value{UPDATED}), a
symlink farm manager which takes distinct sets of software and/or data
located in separate directories on the filesystem, and makes them
appear to be installed in a single directory tree.
@end ifnottex

@menu
* Introduction::                Description of Stow.
* Terminology::                 Terms used by this manual.
* Invoking Stow::               Option summary.
* Ignore Lists::                Controlling what gets stowed.
* Installing Packages::         Using Stow to install.
* Deleting Packages::           Using Stow to uninstall.
* Conflicts::                   When Stow can't stow.
* Mixing Operations::           Multiple actions per invocation.
* Multiple Stow Directories::   Further segregating software.
* Target Maintenance::          Cleaning up mistakes.
* Resource Files::              Setting default command line options.
* Compile-time vs. Install-time::  Faking out `make install'.
* Bootstrapping::               When stow and perl are not yet stowed.
* Reporting Bugs::              How, what, where, and when to report.
* Known Bugs::                  Don't report any of these.
* GNU General Public License::  Copying terms.
* Index::                       Index of concepts.

@detailmenu
 --- The Detailed Node Listing ---

Ignore Lists

* Motivation For Ignore Lists::
* Types And Syntax Of Ignore Lists::
* Justification For Yet Another Set Of Ignore Files::

Advice on changing compilation and installation parameters

* GNU Emacs::
* Other FSF Software::
* Cygnus Software::
* Perl and Perl 5 Modules::

@end detailmenu
@end menu

@c ===========================================================================
@node Introduction, Terminology, Top, Top
@chapter Introduction

GNU Stow is a symlink farm manager which takes distinct sets of
software and/or data located in separate directories on the
filesystem, and makes them all appear to be installed in a single
directory tree.

Originally Stow was born to address the need to administer, upgrade,
install, and remove files in independent software packages without
confusing them with other files sharing the same file system space.
For instance, many years ago it used to be common to compile programs
such as Perl and Emacs from source and install them in
@file{/usr/local}.  When one does so, one winds up with the following
files@footnote{As of Perl 4.036 and Emacs 19.22.  These are now
ancient releases but the example still holds valid.} in
@file{/usr/local/man/man1}:

@example
a2p.1
ctags.1
emacs.1
etags.1
h2ph.1
perl.1
s2p.1
@end example

@noindent
Now suppose it's time to uninstall Perl.  Which man pages
get removed?  Obviously @file{perl.1} is one of them, but it should not
be the administrator's responsibility to memorize the ownership of
individual files by separate packages.

The approach used by Stow is to install each package into its own
tree, then use symbolic links to make it appear as though the files are
installed in the common tree.  Administration can be performed in the
package's private tree in isolation from clutter from other packages.
Stow can then be used to update the symbolic links.  The structure
of each private tree should reflect the desired structure in the common
tree; i.e. (in the typical case) there should be a @file{bin} directory
containing executables, a @file{man/man1} directory containing section 1
man pages, and so on.

While this is useful for keeping track of system-wide and per-user
installations of software built from source, in more recent times
software packages are often managed by more sophisticated package
management software such as
@uref{https://en.wikipedia.org/wiki/Rpm_(software), @command{rpm}},
@uref{https://en.wikipedia.org/wiki/Dpkg, @command{dpkg}}, and
@uref{https://en.wikipedia.org/wiki/Nix_package_manager, Nix} /
@uref{https://en.wikipedia.org/wiki/GNU_Guix, GNU Guix}, or
language-native package managers such as
@uref{https://en.wikipedia.org/wiki/RubyGems, Ruby's @command{gem}},
@uref{https://en.wikipedia.org/wiki/Pip_(package_manager), Python's
@command{pip}}, @uref{https://en.wikipedia.org/wiki/Npm_(software),
Javascript's @command{npm}}, and so on.

However Stow is still used not only for software package management,
but also for other purposes, such as facilitating a more controlled
approach to management of configuration files in the user's home
directory@footnote{@uref{http://brandon.invergo.net/news/2012-05-26-using-gnu-stow-to-manage-your-dotfiles.html}},
especially when coupled with version control
systems@footnote{@uref{http://lists.gnu.org/archive/html/info-stow/2011-12/msg00000.html}}.

Stow was inspired by Carnegie Mellon's Depot program, but is
substantially simpler and safer.  Whereas Depot required database
files to keep things in sync, Stow stores no extra state between runs,
so there's no danger (as there was in Depot) of mangling directories
when file hierarchies don't match the database.  Also unlike Depot,
Stow will never delete any files, directories, or links that appear in
a Stow directory (e.g., @file{/usr/local/stow/emacs}), so it's always
possible to rebuild the target tree (e.g., @file{/usr/local}).

Stow is implemented as a combination of a Perl script providing a CLI
interface, and a backend Perl module which does most of the work.

For information about the latest version of Stow, you can refer to
@uref{http://www.gnu.org/software/stow/}.


@c ===========================================================================
@node Terminology, Invoking Stow, Introduction, Top
@chapter Terminology

@indent
@cindex package
A @dfn{package} is a related collection of files and directories that
you wish to administer as a unit --- e.g., Perl or Emacs --- and that needs
to be installed in a particular directory structure --- e.g., with
@file{bin}, @file{lib}, and @file{man} subdirectories.

@cindex target directory
A @dfn{target directory} is the root of a tree in which one or more
packages wish to @emph{appear} to be installed.  @file{/usr/local} is a
common choice for this, but by no means the only such location.  Another
common choice is @file{~} (i.e.@: the user's @code{$HOME} directory) in
the case where Stow is being used to manage the user's configuration
(``dotfiles'') and other files in their @code{$HOME}.  The examples in
this manual will use @file{/usr/local} as the target directory.

@cindex stow directory
A @dfn{stow directory} is the root of a tree containing separate
packages in private subtrees.  When Stow runs, it uses the current
directory as the default stow directory.  The examples in this manual
will use @file{/usr/local/stow} as the stow directory, so that
individual packages will be, for example, @file{/usr/local/stow/perl}
and @file{/usr/local/stow/emacs}.

@cindex installation image
An @dfn{installation image} is the layout of files and directories
required by a package, relative to the target directory.  Thus, the
installation image for Perl includes: a @file{bin} directory containing
@file{perl} and @file{a2p} (among others); an @file{info} directory
containing Texinfo documentation; a @file{lib/perl} directory containing
Perl libraries; and a @file{man/man1} directory containing man pages.

@quotation Note
This is a @emph{pre-}installation image which exists even before Stow
has installed any symlinks into the target directory which point to it.
@end quotation

@cindex package directory
@cindex package name
A @dfn{package directory} is the root of a tree containing the
installation image for a particular package.  Each package directory
must reside in a stow directory --- e.g., the package directory
@file{/usr/local/stow/perl} must reside in the stow directory
@file{/usr/local/stow}.  The @dfn{name} of a package is the name of its
directory within the stow directory --- e.g., @file{perl}.

Thus, the Perl executable might reside in
@file{/usr/local/stow/perl/bin/perl}, where @file{/usr/local} is the
target directory, @file{/usr/local/stow} is the stow directory,
@file{/usr/local/stow/perl} is the package directory, and
@file{bin/perl} within is part of the installation image.

@anchor{symlink}
@cindex symlink
@cindex symlink source
@cindex symlink destination
@cindex relative symlink
@cindex absolute symlink
A @dfn{symlink} is a symbolic link, i.e.@: an entry on the filesystem
whose path is sometimes called the @dfn{symlink source}, which points to
another location on the filesystem called the @dfn{symlink destination}.
There is no guarantee that the destination actually exists.

In general, symlinks can be @dfn{relative} or @dfn{absolute}.  A symlink
is absolute when the destination names a full path; that is, one
starting from @file{/}.  A symlink is relative when the destination
names a relative path; that is, one not starting from @file{/}.  The
destination of a relative symlink is computed starting from the
symlink's own directory, i.e.@: the directory containing the symlink
source.

@quotation Note
Stow only creates symlinks within the target directory which point to
locations @emph{outside} the target directory and inside the stow
directory.

Consequently, we avoid referring to symlink destinations as symlink
@emph{targets}, since this would result in the word ``target'' having
two different meanings:

@enumerate

@item
the target directory, i.e.@: the directory into which Stow targets
installation, where symlinks are managed by Stow, and

@item
the destinations of those symlinks.

@end enumerate

If we did not avoid the second meaning of ``target'', then it would lead
to confusing language, such as describing Stow as installing symlinks
into the target directory which point to targets @emph{outside} the
target directory.

Similarly, the word ``source'' can have two different meanings in this
context:

@enumerate

@item
the installation image, or some of its contents, and

@item
the location of symlinks (the ``source'' of the link, vs.@: its
destination).

@end enumerate

Therefore it should also be avoided, or at least care taken to ensure
that the meaning is not ambiguous.

@end quotation

@c ===========================================================================
@node Invoking Stow, Ignore Lists, Terminology, Top
@chapter Invoking Stow

The syntax of the @command{stow} command is:

@example
stow [@var{options}] [@var{action flag}] @var{package @dots{}}
@end example

@noindent
Each @var{package} is the name of a package (e.g., @samp{perl}) in the stow
directory that we wish to install into (or delete from) the target directory.
The default action is to install the given packages, although alternate actions
may be specified by preceding the package name(s) with an @var{action flag}.

@noindent
The following options are supported:

@table @samp

@item -d @var{dir}
@itemx --dir=@var{dir}
Set the stow directory to @var{dir}.  Defaults to the value of the environment
variable @env{STOW_DIR} if set, or the current directory otherwise.

@item -t @var{dir}
@itemx --target=@var{dir}
Set the target directory to @var{dir} instead of the parent of the stow
directory.  Defaults to the parent of the stow directory, so it is typical to
execute @command{stow} from the directory @file{/usr/local/stow}.

@item --ignore=@var{regexp}
This (repeatable) option lets you suppress acting on files that match the
given Perl regular expression.  For example, using the options

@example
--ignore='.*\.orig' --ignore='.*\.dist'
@end example

@noindent
will cause stow to ignore files ending in @file{.orig} or @file{.dist}.

Note that the regular expression is anchored to the end of the filename,
because this is what you will want to do most of the time.

Also note that by default Stow automatically ignores a ``sensible''
built-in list of files and directories such as @file{CVS}, editor
backup files, and so on.  @xref{Ignore Lists}, for more details.

@item --defer=@var{regexp}
This (repeatable) option avoids stowing a file matching the given
regular expression, if that file is already stowed by another package.
This is effectively the opposite of @option{--override}.

(N.B. the name @option{--defer} was chosen in the sense that the package
currently being stowed is treated with lower precedence than any
already installed package, not in the sense that the operation is
being postponed to be run at a later point in time; do not confuse
this nomenclature with the wording used in @ref{Deferred Operation}.)

For example, the following options

@example
--defer=man --defer=info
@end example

@noindent
will cause stow to skip over pre-existing man and info pages.

Equivalently, you could use @samp{--defer='man|info'} since the
argument is just a Perl regular expression.

Note that the regular expression is anchored to the beginning of the path
relative to the target directory, because this is what you will want to do most
of the time.

@item --override=@var{regexp}
This (repeatable) option forces any file matching the regular expression to be
stowed, even if the file is already stowed to another package. For example,
the following options

@example
--override=man --override=info
@end example

@noindent
will permit stow to overwrite links that point to pre-existing man and info
pages that are owned by stow and would otherwise cause a conflict.

The regular expression is anchored to the beginning of the path relative to
the target directory, because this is what you will want to do most of the time.

@cindex dotfiles
@item --dotfiles

Enable special handling for @emph{dotfiles} (files or folders whose
name begins with a period) in the package directory. If this option is
enabled, Stow will add a preprocessing step for each file or folder
whose name begins with @samp{dot-}, and replace the @samp{dot-} prefix
in the name by a period @samp{.}. This is useful when Stow is used to
manage collections of dotfiles, to avoid having a package directory
full of hidden files.

For example, suppose we have a package containing two files,
@file{stow/dot-bashrc} and @file{stow/dot-emacs.d/init.el}. With this
option, Stow will create symlinks from @file{.bashrc} to
@file{stow/dot-bashrc} and from @file{.emacs.d/init.el} to
@file{stow/dot-emacs.d/init.el}. Any other files, whose name does not
begin with @samp{dot-}, will be processed as usual.

@item --no-folding

This disables any further tree folding (@pxref{tree folding}) or
refolding (@pxref{tree refolding}).  If a new subdirectory is
encountered whilst stowing a new package, the subdirectory is created
within the target, and its contents are symlinked, rather than just
creating a symlink for the directory.  If removal of symlinks whilst
unstowing a package causes a subtree to be foldable (i.e.@: only
containing symlinks to a single package), that subtree will not be
removed and replaced with a symlink.

@cindex adopting existing files
@item --adopt
@strong{Warning!} This behaviour is specifically intended to alter the
contents of your stow directory.  If you do not want that, this option
is not for you.

When stowing, if a target is encountered which already exists but is a
plain file (and hence not owned by any existing stow package), then
normally Stow will register this as a conflict and refuse to proceed.
This option changes that behaviour so that the file is moved to the
same relative place within the package's installation image within the
stow directory, and then stowing proceeds as before.  So effectively,
the file becomes adopted by the stow package, without its contents
changing.

This is particularly useful when the stow package is under the control
of a version control system, because it allows files in the target
tree, with potentially different contents to the equivalent versions
in the stow package's installation image, to be adopted into the
package, then compared by running something like @samp{git diff ...}
inside the stow package, and finally either kept (e.g. via @samp{git
commit ...}) or discarded (@samp{git checkout HEAD ...}).

@cindex dry run
@cindex simulated run
@item -n
@itemx --no
@itemx --simulate
Do not perform any operations that modify the file system; in combination with
@option{-v} can be used to merely show what would happen.

@cindex verbosity levels
@item -v
@itemx --verbose[=@var{n}]
Send verbose output to standard error describing what Stow is
doing.  Verbosity levels are from 0 to 5; 0 is the default.  Using
@option{-v} or @option{--verbose} increases the verbosity by one; using
@samp{--verbose=@var{n}} sets it to @var{n}.

@item -p
@itemx --compat
Scan the whole target tree when unstowing.  By default, only
directories specified in the @dfn{installation image} are scanned
during an unstow operation.  Scanning the whole tree can be
prohibitive if your target tree is very large.  This option restores
the legacy behaviour; however, the @option{--badlinks} option to the
@command{chkstow} utility may be a better way of ensuring that your
installation does not have any dangling symlinks (@pxref{Target
Maintenance}).

@item -V
@itemx --version
Show Stow version number, and exit.

@item -h
@itemx --help
Show Stow command syntax, and exit.
@end table

The following @var{action flags} are supported:

@table @samp
@item -D
@itemx --delete
Delete (unstow) the package name(s) that follow this option from the @dfn{target
directory}. This option may be repeated any number of times.

@item -R
@itemx --restow
Restow (first unstow, then stow again) the package names that follow this
option.  This is useful for pruning obsolete symlinks from the target tree
after updating the software in a package. This option may be repeated any
number of times.

@item -S
@item --stow
explictly stow the package name(s) that follow this option.  May be
omitted if you are not using the @option{-D} or @option{-R} options in the
same invocation.  @xref{Mixing Operations}, for details of when you
might like to use this feature. This option may be repeated any number
of times.
@end table


@c ===========================================================================
@node Ignore Lists, Installing Packages, Invoking Stow, Top
@chapter Ignore Lists

@cindex ignore lists
@cindex ignoring files and directories

@menu
* Motivation For Ignore Lists::
* Types And Syntax Of Ignore Lists::
* Justification For Yet Another Set Of Ignore Files::
@end menu

@c ===========================================================================
@node Motivation For Ignore Lists, Types And Syntax Of Ignore Lists, Ignore Lists, Ignore Lists
@section Motivation For Ignore Lists

In many situations, there will exist files under the package
directories which it would be undesirable to stow into the target
directory.  For example, files related version control such as
@file{.gitignore}, @file{CVS}, @file{*,v} (RCS files) should typically
not have symlinks from the target tree pointing to them.  Also there
may be files or directories relating to the build of the package which
are not needed at run-time.

In these cases, it can be rather cumbersome to specify a
@option{--ignore} parameter for each file or directory to be ignored.
This could be worked around by ensuring the existence of
@file{~/.stowrc} containing multiple @option{--ignore} lines, or if a
different set of files/directories should be ignored depending on
which stow package is involved, a @file{.stowrc} file for each stow
package, but this would require the user to ensure that they were in
the correct directory before invoking stow, which would be tedious and
error-prone.  Furthermore, since Stow shifts parameters from
@file{.stowrc} onto ARGV at run-time, it could clutter up the process
table with excessively long parameter lists, or even worse, exceed the
operating system's limit for process arguments.

@cindex ignore lists
Therefore in addition to @option{--ignore} parameters, Stow provides a
way to specify lists of files and directories to ignore.

@c ===========================================================================
@node Types And Syntax Of Ignore Lists, Justification For Yet Another Set Of Ignore Files, Motivation For Ignore Lists, Ignore Lists
@section Types And Syntax Of Ignore Lists

If you put Perl regular expressions, one per line, in a
@file{.stow-local-ignore} file within any top level package directory,
in which case any file or directory within that package matching any
of these regular expressions will be ignored.  In the absence of this
package-specific ignore list, Stow will instead use the contents of
@file{~/.stow-global-ignore}, if it exists.  If neither the
package-local or global ignore list exist, Stow will use its own
built-in default ignore list, which serves as a useful example of the
format of these ignore list files:

@example
@verbatiminclude default-ignore-list
@end example

Stow first iterates through the chosen ignore list (built-in, global,
or package-local) as per above, stripping out comments (if you want to
include the @samp{#} symbol in a regular expression, escape it with a
blackslash) and blank lines, placing each regular expressions into one
of two sets depending on whether it contains the @samp{/} forward
slash symbol.

Then in order to determine whether a file or directory should be
ignored:

@enumerate
@item
Stow calculates its path relative to the top-level package directory,
prefixing that with @samp{/}.  If any of the regular expressions
containing a @samp{/} @emph{exactly}@footnote{Exact matching means the
regular expression is anchored at the beginning and end, in contrast
to unanchored regular expressions which will match a substring.} match
a subpath@footnote{In this context, ``subpath'' means a contiguous
subset of path segments; e.g for the relative path
@file{one/two/three}, there are six valid subpaths: @file{one},
@file{two}, @file{three}, @file{one/two}, @file{two/three},
@file{one/two/three}.} of this relative path, then the file or
directory will be ignored.

@item
If none of the regular expressions containing a @samp{/} match in the
manner described above, Stow checks whether the
@emph{basename}@footnote{The ``basename'' is the name of the file or
directory itself, excluding any directory path prefix - as returned by
the @command{basename} command.} of the file or directory matches
@emph{exactly} against the remaining regular expressions which do not
contain a @samp{/}, and if so, ignores the file or directory.

@item
Otherwise, the file or directory is not ignored.
@end enumerate

@c N.B. if you change the examples below, please also consider
@c updating test_examples_in_manual() in t/ignore.t.

For example, if a file @file{bazqux} is in the @file{foo/bar}
subdirectory of the package directory, Stow would use
@samp{/foo/bar/bazqux} as the text for matching against regular
expressions which contain @samp{/}, and @samp{bazqux} as the text for
matching against regular expressions which don't contain @samp{/}.
Then regular expressions @samp{bazqux}, @samp{baz.*}, @samp{.*qux},
@samp{bar/.*x}, and @samp{^/foo/.*qux} would all match (causing the
file to be ignored), whereas @samp{bar}, @samp{baz}, @samp{qux}, and
@samp{o/bar/b} would not (although @samp{bar} would cause its parent
directory to be ignored and prevent Stow from recursing into that
anyway, in which case the file @file{bazqux} would not even be
considered for stowing).

As a special exception to the above algorithm, any
@file{.stow-local-ignore} present in the top-level package directory
is @emph{always} ignored, regardless of the contents of any ignore
list, because this file serves no purpose outside the stow directory.

@c ===========================================================================
@node Justification For Yet Another Set Of Ignore Files,  , Types And Syntax Of Ignore Lists, Ignore Lists
@section Justification For Yet Another Set Of Ignore Files

The reader may note that this format is very similar to existing
ignore list file formats, such as those for @command{cvs}, @command{git},
@command{rsync} etc., and wonder if another set of ignore lists is
justified.  However there are good reasons why Stow does not simply
check for the presence of say, @file{.cvsignore}, and use that if it
exists.  Firstly, there is no guarantee that a stow package would
contain any version control meta-data, or permit introducing this if
it didn't already exist.

Secondly even if it did, version control system ignore lists generally
reflect @emph{build-time} ignores rather than @emph{install-time}, and
there may be some intermediate or temporary files on those ignore
lists generated during development or at build-time which it would be
inappropriate to stow, even though many files generated at build-time
(binaries, libraries, documentation etc.) certainly do need to be
stowed.  Similarly, if a file is @emph{not} in the version control
system's ignore list, there is no way of knowing whether the file is
intended for end use, let alone whether the version control system is
tracking it or not.

Therefore it seems clear that ignore lists provided by version control
systems do not provide sufficient information for Stow to determine
which files and directories to stow, and so it makes sense for Stow to
support independent ignore lists.

@c ===========================================================================
@node Installing Packages, Deleting Packages, Ignore Lists, Top
@chapter Installing Packages

@cindex installation
The default action of Stow is to install a package.  This means creating
symlinks in the target tree that point into the package tree.  Stow
attempts to do this with as few symlinks as possible; in other words, if
Stow can create a single symlink that points to an entire subtree within
the package tree, it will choose to do that rather than create a
directory in the target tree and populate it with symlinks.

@anchor{tree folding}
@section Tree folding
@cindex tree folding
@cindex directory folding
@cindex folding trees
For example, suppose that no packages have yet been installed in
@file{/usr/local}; it's completely empty (except for the @file{stow}
subdirectory, of course).  Now suppose the Perl package is installed.
Recall that it includes the following directories in its installation
image:  @file{bin}; @file{info}; @file{lib/perl}; @file{man/man1}.
Rather than creating the directory @file{/usr/local/bin} and populating
it with symlinks to @file{../stow/perl/bin/perl} and
@file{../stow/perl/bin/a2p} (and so on), Stow will create a
single symlink, @file{/usr/local/bin}, which points to
@file{stow/perl/bin}.  In this way, it still works to refer to
@file{/usr/local/bin/perl} and @file{/usr/local/bin/a2p}, and fewer
symlinks have been created.  This is called @dfn{tree folding}, since an
entire subtree is ``folded'' into a single symlink.

To complete this example, Stow will also create the symlink
@file{/usr/local/info} pointing to @file{stow/perl/info}; the symlink
@file{/usr/local/lib} pointing to @file{stow/perl/lib}; and the symlink
@file{/usr/local/man} pointing to @file{stow/perl/man}.

Now suppose that instead of installing the Perl package into an empty
target tree, the target tree is not empty to begin with.  Instead, it
contains several files and directories installed under a different
system-administration philosophy.  In particular, @file{/usr/local/bin}
already exists and is a directory, as are @file{/usr/local/lib} and
@file{/usr/local/man/man1}.  In this case, Stow will descend into
@file{/usr/local/bin} and create symlinks to
@file{../stow/perl/bin/perl} and @file{../stow/perl/bin/a2p} (etc.),
and it will descend into @file{/usr/local/lib} and create the
tree-folding symlink @file{perl} pointing to
@file{../stow/perl/lib/perl}, and so on.  As a rule, Stow only
descends as far as necessary into the target tree when it can create a
tree-folding symlink.  However, this behaviour can be changed via
the @option{--no-folding} option; @pxref{Invoking Stow}.

@anchor{Tree unfolding}
@section Tree unfolding
@cindex splitting open folded trees
@cindex unfolding trees
@cindex tree unfolding
@cindex tree unsplitting
The time often comes when a tree-folding symlink has to be undone
because another package uses one or more of the folded subdirectories in
its installation image.  This operation is called @dfn{splitting open} or
@dfn{unfolding} a folded tree.  It involves removing the original symlink from
the target tree, creating a true directory in its place, and then populating the
new directory with symlinks to the newly-installed package @emph{and} to
the old package that used the old symlink.  For example, suppose that
after installing Perl into an empty @file{/usr/local}, we wish to
install Emacs.  Emacs's installation image includes a @file{bin}
directory containing the @file{emacs} and @file{etags} executables,
among others.  Stow must make these files appear to be installed
in @file{/usr/local/bin}, but presently @file{/usr/local/bin} is a
symlink to @file{stow/perl/bin}.  Stow therefore takes the
following steps:  the symlink @file{/usr/local/bin} is deleted; the
directory @file{/usr/local/bin} is created; links are made from
@file{/usr/local/bin} to @file{../stow/emacs/bin/emacs} and
@file{../stow/emacs/bin/etags}; and links are made from
@file{/usr/local/bin} to @file{../stow/perl/bin/perl} and
@file{../stow/perl/bin/a2p}.

@section Ownership
@cindex ownership
When splitting open a folded tree, Stow makes sure that the
symlink it is about to remove points inside a valid package in the
current stow directory.  @emph{Stow will never delete anything
that it doesn't own}.  Stow ``owns'' everything living in the
target tree that points into a package in the stow directory.  Anything
Stow owns, it can recompute if lost: symlinks that point into a package in
the stow directory, or directories that only contain symlinks that stow
``owns''.   Note that by this definition, Stow doesn't ``own'' anything
@emph{in} the stow directory or in any of the packages.

@section Conflicts during installation
@cindex conflicts
@cindex installation conflicts
If Stow needs to create a directory or a symlink in the target
tree and it cannot because that name is already in use and is not owned
by Stow, then a @dfn{conflict} has arisen.  @xref{Conflicts}.


@c ===========================================================================
@node Deleting Packages, Conflicts, Installing Packages, Top
@chapter Deleting Packages

@cindex deletion
When the @option{-D} option is given, the action of Stow is to
delete a package from the target tree.  Note that Stow will not
delete anything it doesn't ``own''.  Deleting a package does @emph{not}
mean removing it from the stow directory or discarding the package
tree.

To delete a package, Stow recursively scans the target tree, skipping over any
directory that is not included in the installation image.@footnote{This
approach was introduced in version 2 of GNU Stow.  Previously, the whole
target tree was scanned and stow directories were explicitly omitted.  This
became problematic when dealing with very large installations.  The only
situation where this is useful is if you accidentally delete a directory in
the package tree, leaving you with a whole bunch of dangling links.  Note that
you can enable the old approach with the @option{-p} option.  Alternatively, you can
use the @option{--badlinks} option get stow to search for dangling links in your target tree and remove the offenders manually.}
For example, if the target directory is @file{/usr/local} and the
installation image for the package being deleted has only a @file{bin}
directory and a @file{man} directory at the top level, then we only scan
@file{/usr/local/bin} and  @file{/usr/local/man}, and not
@file{/usr/local/lib} or @file{/usr/local/share}, or for that matter
@file{/usr/local/stow}.  Any symlink it finds that points into the package
being deleted is removed.  Any directory that contained only symlinks to the
package being deleted is removed.

@anchor{tree refolding}
@section Refolding ``foldable'' trees.
@cindex refolding trees
@cindex tree refolding

After removing symlinks and empty subdirectories, any directory that
contains only symlinks to a single other package is considered to be a
previously ``folded'' tree that was ``split open.''  Stow will refold
the tree by removing the symlinks to the surviving package, removing
the directory, then linking the directory back to the surviving
package.  However, this behaviour can be prevented via the
@option{--no-folding} option; @pxref{Invoking Stow}.

@c ===========================================================================
@node Conflicts, Mixing Operations, Deleting Packages, Top
@chapter Conflicts

@cindex conflicts
If, during installation, a file or symlink exists in the target tree and
has the same name as something Stow needs to create, and if the
existing name is not a folded tree that can be split open, then a
@dfn{conflict} has arisen.  A conflict also occurs if a directory exists
where Stow needs to place a symlink to a non-directory.  On the
other hand, if the existing name is merely a symlink that already points
where Stow needs it to, then no conflict has occurred.  (Thus it
is harmless to install a package that has already been installed.)

For complex packages, scanning the stow and target trees in tandem,
and deciding whether to make directories or links, split-open or fold
directories, can actually take a long time (a number of seconds).
Moreover, an accurate analysis of potential conflicts requires us to
take into account all of these operations.

@anchor{Deferred Operation}
@section Deferred Operation
@cindex deferred operation

Since version 2.0, Stow now adopts a two-phase algorithm, first
scanning for any potential conflicts before any stowing or unstowing
operations are performed.  If any conflicts are found, they are
displayed and then Stow terminates without making any modifications to
the filesystem.  This means that there is much less risk of a package
being partially stowed or unstowed due to conflicts.

Prior to version 2.0, if a conflict was discovered, the stow or unstow
operation could be aborted mid-flow, leaving the target tree in an
inconsistent state.

@c ===========================================================================
@node Mixing Operations, Multiple Stow Directories, Conflicts, Top
@chapter Mixing Operations
@cindex mixing operations

Since version 2.0, multiple distinct actions can be specified in a single
invocation of GNU Stow.  For example, to update an installation of Emacs from
version 21.3 to 21.4a you can now do the following:

@example
stow -D emacs-21.3 -S emacs-21.4a
@end example

@noindent
which will replace emacs-21.3 with emacs-21.4a using a single invocation.

@cindex deferred operation
This is much faster and cleaner than performing two separate
invocations of stow, because redundant folding/unfolding operations
can be factored out.  In addition, all the operations are calculated
and merged before being executed (@pxref{Deferred Operation}), so the
amount of time in which GNU Emacs is unavailable is minimised.

You can mix and match any number of actions, for example,

@example
stow -S pkg1 pkg2 -D pkg3 pkg4 -S pkg5 -R pkg6
@end example

@noindent
will unstow pkg3, pkg4 and pkg6, then stow pkg1, pkg2, pkg5 and pkg6.

@c ===========================================================================
@node Multiple Stow Directories, Target Maintenance, Mixing Operations, Top
@chapter Multiple Stow Directories

If there are two or more system administrators who wish to maintain
software separately, or if there is any other reason to want two or more
stow directories, it can be done by creating a file named @file{.stow}
in each stow directory.  The presence of @file{/usr/local/foo/.stow}
informs Stow that, though @file{foo} is not the current stow
directory, even if it is a subdirectory of the target directory,
nevertheless it is @emph{a} stow directory and as such Stow
doesn't ``own'' anything in it (@pxref{Installing Packages}).  This will
protect the contents of @file{foo} from a @samp{stow -D}, for instance.

@c There is a test for the following case in t/examples.t:

When multiple stow directories share a target tree, if a tree-folding
symlink is encountered and needs to be split open during an
installation, as long as the top-level stow directory into which the
existing symlink points contains @file{.stow}, Stow knows how to split
open the tree in the correct manner.

@c ===========================================================================
@node Target Maintenance, Resource Files, Multiple Stow Directories, Top
@chapter Target Maintenance

@cindex maintenance
From time to time you will need to clean up your target tree.  Since
version 2, Stow provides a new utility @command{chkstow} to help with
this.  It includes three operational modes which performs checks that
would generally be too expensive to be performed during normal stow
execution.

The syntax of the @command{chkstow} command is:

@example
chkstow [@var{options}]
@end example

@noindent
The following options are supported:

@table @samp

@item -t @var{dir}
@itemx --target=@var{dir}
Set the target directory to @var{dir} instead of the parent of the stow
directory.  Defaults to the parent of the stow directory, so it is typical to
execute @command{stow} from the directory @file{/usr/local/stow}.

@item -b
@itemx --badlinks
Checks target directory for bogus symbolic links. That is, links that point to
non-existent files.

@item -a
@itemx --aliens
Checks for files in the target directory that are not symbolic links. The
target directory should be managed by stow alone, except for directories that
contain a @file{.stow} file.

@item -l
@itemx --list
Will display the target package for every symbolic link in the stow target
directory.

@end table

@c ===========================================================================
@node Resource Files, Compile-time vs. Install-time, Target Maintenance, Top
@chapter Resource Files
@cindex resource files
@cindex configuration files

Default command line options may be set in @file{.stowrc} (current
directory) or @file{~/.stowrc} (home directory). These are parsed in
that order, and are appended together if they both exist. The effect of
the options in the resource file is similar to simply prepending the
options to the command line. This feature can be used for some
interesting effects.

For example, suppose your site uses more than one stow directory, perhaps in
order to share around responsibilities with a number of systems
administrators. One of the administrators might have the following in their
@file{~/.stowrc} file:

@example
--dir=/usr/local/stow2
--target=/usr/local
--ignore='~'
--ignore='^CVS'
@end example

so that the @command{stow} command will default to operating on the
@file{/usr/local/stow2} directory, with @file{/usr/local} as the
target, and ignoring vi backup files and CVS directories.

If you had a stow directory @file{/usr/local/stow/perl-extras} that
was only used for Perl modules, then you might place the following in
@file{/usr/local/stow/perl-extras/.stowrc}:

@example
--dir=/usr/local/stow/perl-extras
--target=/usr/local
--override=bin
--override=man
--ignore='perllocal\.pod'
--ignore='\.packlist'
--ignore='\.bs'
@end example

so that when you are in the @file{/usr/local/stow/perl-extras}
directory, @command{stow} will regard any subdirectories as stow
packages, with @file{/usr/local} as the target (rather than the
immediate parent directory @file{/usr/local/stow}), overriding any
pre-existing links to bin files or man pages, and ignoring some cruft
that gets installed by default.

If an option is provided both on the command line and in a resource file,
the command line option takes precedence. For options that provide a single
value, such as @command{--target} or @command{--dir}, the command line
option will overwrite any options in the resource file. For options that can
be given more than once, @command{--ignore} for example, command line
options and resource options are appended together.

For options that take a file path, environment variables and the tilde
character (@command{~}) are expanded. An environment variable can be
given in either the @command{$VAR} or @command{$@{VAR@}} form. To
prevent expansion, escape the @command{$} or @command{~} with a
backslash.

The options @command{-D}, @command{-S}, and @command{-R} are ignored in
resource files. This is also true of any package names given in the
resource file.

@c ===========================================================================
@node Compile-time vs. Install-time, Bootstrapping, Resource Files, Top
@chapter Compile-time vs. Install-time

Software whose installation is managed with Stow needs to be installed
in one place (the package directory, e.g. @file{/usr/local/stow/perl})
but needs to appear to run in another place (the target tree, e.g.,
@file{/usr/local}).  Why is this important?  What's wrong with Perl, for
instance, looking for its files in @file{/usr/local/stow/perl} instead
of in @file{/usr/local}?

The answer is that there may be another package, e.g.,
@file{/usr/local/stow/perl-extras}, stowed under @file{/usr/local}.  If
Perl is configured to find its files in @file{/usr/local/stow/perl}, it
will never find the extra files in the @samp{perl-extras} package, even
though they're intended to be found by Perl.  On the other hand, if Perl
looks for its files in @file{/usr/local}, then it will find the
intermingled Perl and @samp{perl-extras} files.

This means that when you compile a package, you must tell it the
location of the run-time, or target tree; but when you install it, you
must place it in the stow tree.

@section Advice on changing compilation and installation parameters
Some software packages allow you to specify, at compile-time, separate
locations for installation and for run-time.  Perl is one such package;
see @ref{Perl and Perl 5 Modules}.  Others allow you to compile the
package, then give a different destination in the @samp{make install}
step without causing the binaries or other files to get rebuilt.  Most
GNU software falls into this category; Emacs is a notable exception.
@xref{GNU Emacs}, and @ref{Other FSF Software}.

Still other software packages cannot abide the idea of separate
installation and run-time locations at all.  If you try to @samp{make
install prefix=/usr/local/stow/@var{foo}}, then first the whole package
will be recompiled to hardwire the @file{/usr/local/stow/@var{foo}}
path.  With these packages, it is best to compile normally, then run
@samp{make -n install}, which should report all the steps needed to
install the just-built software.  Place this output into a file, edit
the commands in the file to remove recompilation steps and to reflect
the Stow-based installation location, and execute the edited file as a
shell script in place of @samp{make install}.  Be sure to execute the
script using the same shell that @samp{make install} would have used.

(If you use GNU Make and a shell [such as GNU bash] that understands
@command{pushd} and @command{popd}, you can do the following:

@enumerate
@item
Replace all lines matching @samp{make[@var{n}]: Entering directory
@var{dir}} with @samp{pushd @var{dir}}.
@item
Replace all lines matching @samp{make[@var{n}]: Leaving directory
@var{dir}} with @samp{popd}.
@item
Delete all lines matching @samp{make[@var{n}]: Nothing to be done for
@var{rule}}.
@end enumerate

Then find other lines in the output containing @command{cd} or @command{make}
commands and rewrite or delete them.  In particular, you should be able
to delete sections of the script that resemble this:

@example
for i in @var{dir_1} @var{dir_2} @r{@dots{}}; do \
  (cd $i; make @var{args} @r{@dots{}}) \
done
@end example

@noindent
Note, that's ``should be able to,'' not ``can.''  Be sure to modulate
these guidelines with plenty of your own intelligence.

The details of stowing some specific packages are described in the
following sections.

@menu
* GNU Emacs::
* Other FSF Software::
* Cygnus Software::
* Perl and Perl 5 Modules::
@end menu

@c ---------------------------------------------------------------------------
@node GNU Emacs, Other FSF Software, Compile-time vs. Install-time, Compile-time vs. Install-time
@section GNU Emacs

Although the Free Software Foundation has many enlightened practices
regarding Makefiles and software installation (see @pxref{Other FSF
Software}), Emacs, its flagship program, doesn't quite follow the
rules.  In particular, most GNU software allows you to write:

@example
make
make install prefix=/usr/local/stow/@var{package}
@end example

@noindent
If you try this with Emacs, then the new value for @var{prefix} in the
@samp{make install} step will cause some files to get recompiled with
the new value of @var{prefix} wired into them.  In Emacs 19.23 and
later,@footnote{As I write this, the current version of Emacs is 19.31.}
the way to work around this problem is:

@example
make
make install-arch-dep install-arch-indep prefix=/usr/local/stow/emacs
@end example

In 19.22 and some prior versions of Emacs, the workaround was:

@example
make
make do-install prefix=/usr/local/stow/emacs
@end example

@c ---------------------------------------------------------------------------
@node Other FSF Software, Cygnus Software, GNU Emacs, Compile-time vs. Install-time
@section Other FSF Software

The Free Software Foundation, the organization behind the GNU project,
has been unifying the build procedure for its tools for some time.
Thanks to its tools @samp{autoconf} and @samp{automake}, most packages
now respond well to these simple steps, with no other intervention
necessary:

@example
./configure @var{options}
make
make install prefix=/usr/local/stow/@var{package}
@end example

Hopefully, these tools can evolve to be aware of Stow-managed packages,
such that providing an option to @samp{configure} can allow @samp{make}
and @samp{make install} steps to work correctly without needing to
``fool'' the build process.

@c ---------------------------------------------------------------------------
@node Cygnus Software, Perl and Perl 5 Modules, Other FSF Software, Compile-time vs. Install-time
@section Cygnus Software

Cygnus is a commercial supplier and supporter of GNU software.  It has
also written several of its own packages, released under the terms of
the GNU General Public License; and it has taken over the maintenance of
other packages.  Among the packages released by Cygnus are @samp{gdb},
@samp{gnats}, and @samp{dejagnu}.

Cygnus packages have the peculiarity that each one unpacks into a
directory tree with a generic top-level Makefile, which is set up to
compile @emph{all} of Cygnus' packages, any number of which may reside
under the top-level directory.  In other words, even if you're only
building @samp{gnats}, the top-level Makefile will look for, and try to
build, @file{gdb} and @file{dejagnu} subdirectories, among many others.

The result is that if you try @samp{make -n install
prefix=/usr/local/stow/@var{package}} at the top level of a Cygnus
package, you'll get a bewildering amount of output.  It will then be
very difficult to visually scan the output to see whether the install
will proceed correctly.  Unfortunately, it's not always clear how to
invoke an install from the subdirectory of interest.

In cases like this, the best approach is to run your @samp{make install
prefix=@r{@dots{}}}, but be ready to interrupt it if you detect that it
is recompiling files.  Usually it will work just fine; otherwise,
install manually.

@c ---------------------------------------------------------------------------
@node Perl and Perl 5 Modules,  , Cygnus Software, Compile-time vs. Install-time
@section Perl and Perl 5 Modules

Perl 4.036 allows you to specify different locations for installation
and for run-time.  It is the only widely-used package in this author's
experience that allows this, though hopefully more packages will adopt
this model.

Unfortunately, the authors of Perl believed that only AFS sites need
this ability.  The configuration instructions for Perl 4 misleadingly
state that some occult means are used under AFS to transport files from
their installation tree to their run-time tree.  In fact, that confusion
arises from the fact that Depot, Stow's predecessor, originated at
Carnegie Mellon University, which was also the birthplace of AFS.  CMU's
need to separate install-time and run-time trees stemmed from its use of
Depot, not from AFS.

The result of this confusion is that Perl 5's configuration script
doesn't even offer the option of separating install-time and run-time
trees @emph{unless} you're running AFS.  Fortunately, after you've
entered all the configuration settings, Perl's setup script gives you
the opportunity to edit those settings in a file called
@file{config.sh}.  When prompted, you should edit this file and replace
occurrences of

@example
inst@r{@dots{}}/usr/local@r{@dots{}}
@end example

@noindent
with

@example
inst@r{@dots{}}/usr/local/stow/perl@r{@dots{}}
@end example

@noindent
You can do this with the following Unix command:

@example
sed 's,^\(inst.*/usr/local\),\1/stow/perl,' config.sh > config.sh.new
mv config.sh.new config.sh
@end example

Hopefully, the Perl authors will correct this deficiency in Perl 5's
configuration mechanism.

Perl 5 modules---i.e., extensions to Perl 5---generally conform to a set
of standards for building and installing them.  The standard says that
the package comes with a top-level @file{Makefile.PL}, which is a Perl
script.  When it runs, it generates a @file{Makefile}.

If you followed the instructions above for editing @file{config.sh} when
Perl was built, then when you create a @file{Makefile} from a
@file{Makefile.PL}, it will contain separate locations for run-time
(@file{/usr/local}) and install-time (@file{/usr/local/stow/perl}).
Thus you can do

@example
perl Makefile.PL
make
make install
@end example

@noindent
and the files will be installed into @file{/usr/local/stow/perl}.
However, you might prefer each Perl module to be stowed separately.  In
that case, you must edit the resulting Makefile, replacing
@file{/usr/local/stow/perl} with @file{/usr/local/stow/@var{module}}.
The best way to do this is:

@example
perl Makefile.PL
find . -name Makefile -print | \
  xargs perl -pi~ -e 's,^(INST.*/stow)/perl,$1/@var{module},;'
make
make install
@end example

@noindent
(The use of @samp{find} and @samp{xargs} ensures that all Makefiles in
the module's source tree, even those in subdirectories, get edited.)  A
good convention to follow is to name the stow directory for a Perl
@var{module} @file{cpan.@var{module}}, where @samp{cpan} stands for
Comprehensive Perl Archive Network, a collection of FTP sites that is
the source of most Perl 5 extensions.  This way, it's easy to tell at a
glance which of the subdirectories of @file{/usr/local/stow} are Perl 5
extensions.

When you stow separate Perl 5 modules separately, you are likely to
encounter conflicts (@pxref{Conflicts}) with files named @file{.exists}
and @file{perllocal.pod}.  One way to work around this is to remove
those files before stowing the module.  If you use the
@file{cpan.@var{module}} naming convention, you can simply do this:

@example
cd /usr/local/stow
find cpan.* \( -name .exists -o -name perllocal.pod \) -print | \
  xargs rm
@end example


@c ---------------------------------------------------------------------------
@node Bootstrapping, Reporting Bugs, Compile-time vs. Install-time, Top
@chapter Bootstrapping

Suppose you have a stow directory all set up and ready to go:
@file{/usr/local/stow/perl} contains the Perl installation,
@file{/usr/local/stow/stow} contains Stow itself, and perhaps you have
other packages waiting to be stowed.  You'd like to be able to do this:

@example
cd /usr/local/stow
stow -vv *
@end example

@noindent
but @command{stow} is not yet in your @env{PATH}.  Nor can you do this:

@example
cd /usr/local/stow
stow/bin/stow -vv *
@end example

@noindent
because the @samp{#!} line at the beginning of @command{stow} tries to
locate Perl (usually in @file{/usr/local/bin/perl}), and that won't be
found.  The solution you must use is:

@example
cd /usr/local/stow
perl/bin/perl stow/bin/stow -vv *
@end example

@c ===========================================================================
@node Reporting Bugs, Known Bugs, Bootstrapping, Top
@chapter Reporting Bugs

You can report bugs to the current maintainers in one of three ways:

@enumerate
@item
Send e-mail to @email{bug-stow@@gnu.org}.

@item
File an issue in @uref{https://savannah.gnu.org/bugs/?group=stow,
the Savannah bug tracker}.

@item
File an issue in
@uref{https://github.com/aspiers/stow/issues/, the GitHub project}.
@end enumerate

While GitHub is arguably the most convenient of these three options, it
@uref{https://www.gnu.org/software/repo-criteria-evaluation.html#GitHub,
is not the most ethical or freedom-preserving way to host software
projects}.  Therefore the GitHub project may be
@uref{https://github.com/aspiers/stow/issues/43, moved to a more ethical
hosting service} in the future.

Before reporting a bug, it is recommended to check whether it is already
known, so please first @pxref{Known Bugs}.

When reporting a new bug, please include:

@itemize @bullet
@item
the version number of Stow (@samp{stow --version});

@item
the version number of Perl (@samp{perl -v});

@item
the system information, which can often be obtained with @samp{uname
-a};

@item
a description of the bug;

@item
the precise command you gave;

@item
the output from the command (preferably verbose output, obtained by
adding @samp{--verbose=5} to the Stow command line).
@end itemize

If you are really keen, consider developing a minimal test case and
creating a new test.  See the @file{t/} directory in the source for lots
of examples, and the @file{CONTRIBUTING.md} file for a guide on how to
contribute.

Before reporting a bug, please read the manual carefully, especially
@ref{Known Bugs}, to see whether you're encountering
something that doesn't need reporting.
(@pxref{Conflicts}).

@c ===========================================================================
@node Known Bugs, GNU General Public License, Reporting Bugs, Top
@chapter Known Bugs

Known bugs can be found in the following locations:

@itemize
@item
@uref{https://github.com/aspiers/stow/issues/, the GitHub issue tracker}

@item
@uref{https://savannah.gnu.org/bugs/?group=stow, the Savannah bug
tracker}

@item
the @uref{https://lists.gnu.org/archive/html/bug-stow/, bug-stow list
archives}
@end itemize

If you think you have found a new bug, please @pxref{Reporting Bugs}.

@c ===========================================================================
@node GNU General Public License, Index, Known Bugs, Top
@unnumbered GNU General Public License

@center Version 3, 29 June 2007

@c This file is intended to be included within another document,
@c hence no sectioning command or @node.

@display
Copyright @copyright{} 2007 Free Software Foundation, Inc. @url{https://fsf.org/}

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
@end display

@heading Preamble

The GNU General Public License is a free, copyleft license for
software and other kinds of works.

The licenses for most software and other practical works are designed
to take away your freedom to share and change the works.  By contrast,
the GNU General Public License is intended to guarantee your freedom
to share and change all versions of a program---to make sure it remains
free software for all its users.  We, the Free Software Foundation,
use the GNU General Public License for most of our software; it
applies also to any other work released this way by its authors.  You
can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
them if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
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To protect your rights, we need to prevent others from denying you
these rights or asking you to surrender the rights.  Therefore, you
have certain responsibilities if you distribute copies of the
software, or if you modify it: responsibilities to respect the freedom
of others.

For example, if you distribute copies of such a program, whether
gratis or for a fee, you must pass on to the recipients the same
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terms so they know their rights.

Developers that use the GNU GPL protect your rights with two steps:
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For the developers' and authors' protection, the GPL clearly explains
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Some devices are designed to deny users access to install or run
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Finally, every program is threatened constantly by software patents.
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The precise terms and conditions for copying, distribution and
modification follow.

@heading TERMS AND CONDITIONS

@enumerate 0
@item Definitions.

``This License'' refers to version 3 of the GNU General Public License.

``Copyright'' also means copyright-like laws that apply to other kinds
of works, such as semiconductor masks.

``The Program'' refers to any copyrightable work licensed under this
License.  Each licensee is addressed as ``you''.  ``Licensees'' and
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To ``modify'' a work means to copy from or adapt all or part of the work
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A ``covered work'' means either the unmodified Program or a work based
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To ``propagate'' a work means to do anything with it that, without
permission, would make you directly or secondarily liable for
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To ``convey'' a work means any kind of propagation that enables other
parties to make or receive copies.  Mere interaction with a user
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An interactive user interface displays ``Appropriate Legal Notices'' to
the extent that it includes a convenient and prominently visible
feature that (1) displays an appropriate copyright notice, and (2)
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work under this License, and how to view a copy of this License.  If
the interface presents a list of user commands or options, such as a
menu, a prominent item in the list meets this criterion.

@item Source Code.

The ``source code'' for a work means the preferred form of the work for
making modifications to it.  ``Object code'' means any non-source form
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A ``Standard Interface'' means an interface that either is an official
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The ``System Libraries'' of an executable work include anything, other
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The ``Corresponding Source'' for a work in object code form means all
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The Corresponding Source need not include anything that users can
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The Corresponding Source for a work in source code form is that same
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@item Basic Permissions.

All rights granted under this License are granted for the term of
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You may make, run and propagate covered works that you do not convey,
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You may convey covered works to others for the sole purpose of having
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Conveying under any other circumstances is permitted solely under the
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@item Protecting Users' Legal Rights From Anti-Circumvention Law.

No covered work shall be deemed part of an effective technological
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When you convey a covered work, you waive any legal power to forbid
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@item Conveying Verbatim Copies.

You may convey verbatim copies of the Program's source code as you
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keep intact all notices stating that this License and any
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keep intact all notices of the absence of any warranty; and give all
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You may charge any price or no price for each copy that you convey,
and you may offer support or warranty protection for a fee.

@item Conveying Modified Source Versions.

You may convey a work based on the Program, or the modifications to
produce it from the Program, in the form of source code under the
terms of section 4, provided that you also meet all of these
conditions:

@enumerate a
@item
The work must carry prominent notices stating that you modified it,
and giving a relevant date.

@item
The work must carry prominent notices stating that it is released
under this License and any conditions added under section 7.  This
requirement modifies the requirement in section 4 to ``keep intact all
notices''.

@item
You must license the entire work, as a whole, under this License to
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to the whole of the work, and all its parts, regardless of how they
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any other way, but it does not invalidate such permission if you have
separately received it.

@item
If the work has interactive user interfaces, each must display
Appropriate Legal Notices; however, if the Program has interactive
interfaces that do not display Appropriate Legal Notices, your work
need not make them do so.
@end enumerate

A compilation of a covered work with other separate and independent
works, which are not by their nature extensions of the covered work,
and which are not combined with it such as to form a larger program,
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beyond what the individual works permit.  Inclusion of a covered work
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parts of the aggregate.

@item  Conveying Non-Source Forms.

You may convey a covered work in object code form under the terms of
sections 4 and 5, provided that you also convey the machine-readable
Corresponding Source under the terms of this License, in one of these
ways:

@enumerate a
@item
Convey the object code in, or embodied in, a physical product
(including a physical distribution medium), accompanied by the
Corresponding Source fixed on a durable physical medium customarily
used for software interchange.

@item
Convey the object code in, or embodied in, a physical product
(including a physical distribution medium), accompanied by a written
offer, valid for at least three years and valid for as long as you
offer spare parts or customer support for that product model, to give
anyone who possesses the object code either (1) a copy of the
Corresponding Source for all the software in the product that is
covered by this License, on a durable physical medium customarily used
for software interchange, for a price no more than your reasonable
cost of physically performing this conveying of source, or (2) access
to copy the Corresponding Source from a network server at no charge.

@item
Convey individual copies of the object code with a copy of the written
offer to provide the Corresponding Source.  This alternative is
allowed only occasionally and noncommercially, and only if you
received the object code with such an offer, in accord with subsection
6b.

@item
Convey the object code by offering access from a designated place
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Corresponding Source along with the object code.  If the place to copy
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on a different server (operated by you or a third party) that supports
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Regardless of what server hosts the Corresponding Source, you remain
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satisfy these requirements.

@item
Convey the object code using peer-to-peer transmission, provided you
inform other peers where the object code and Corresponding Source of
the work are being offered to the general public at no charge under
subsection 6d.

@end enumerate

A separable portion of the object code, whose source code is excluded
from the Corresponding Source as a System Library, need not be
included in conveying the object code work.

A ``User Product'' is either (1) a ``consumer product'', which means any
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If you convey an object code work under this section in, or with, or
specifically for use in, a User Product, and the conveying occurs as
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User Product is transferred to the recipient in perpetuity or for a
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Corresponding Source conveyed under this section must be accompanied
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if neither you nor any third party retains the ability to install
modified object code on the User Product (for example, the work has
been installed in ROM).

The requirement to provide Installation Information does not include a
requirement to continue to provide support service, warranty, or
updates for a work that has been modified or installed by the
recipient, or for the User Product in which it has been modified or
installed.  Access to a network may be denied when the modification
itself materially and adversely affects the operation of the network
or violates the rules and protocols for communication across the
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Corresponding Source conveyed, and Installation Information provided,
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documented (and with an implementation available to the public in
source code form), and must require no special password or key for
unpacking, reading or copying.

@item Additional Terms.

``Additional permissions'' are terms that supplement the terms of this
License by making exceptions from one or more of its conditions.
Additional permissions that are applicable to the entire Program shall
be treated as though they were included in this License, to the extent
that they are valid under applicable law.  If additional permissions
apply only to part of the Program, that part may be used separately
under those permissions, but the entire Program remains governed by
this License without regard to the additional permissions.

When you convey a copy of a covered work, you may at your option
remove any additional permissions from that copy, or from any part of
it.  (Additional permissions may be written to require their own
removal in certain cases when you modify the work.)  You may place
additional permissions on material, added by you to a covered work,
for which you have or can give appropriate copyright permission.

Notwithstanding any other provision of this License, for material you
add to a covered work, you may (if authorized by the copyright holders
of that material) supplement the terms of this License with terms:

@enumerate a
@item
Disclaiming warranty or limiting liability differently from the terms
of sections 15 and 16 of this License; or

@item
Requiring preservation of specified reasonable legal notices or author
attributions in that material or in the Appropriate Legal Notices
displayed by works containing it; or

@item
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@item
Limiting the use for publicity purposes of names of licensors or
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@item
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names, trademarks, or service marks; or

@item
Requiring indemnification of licensors and authors of that material by
anyone who conveys the material (or modified versions of it) with
contractual assumptions of liability to the recipient, for any
liability that these contractual assumptions directly impose on those
licensors and authors.
@end enumerate

All other non-permissive additional terms are considered ``further
restrictions'' within the meaning of section 10.  If the Program as you
received it, or any part of it, contains a notice stating that it is
governed by this License along with a term that is a further
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a further restriction but permits relicensing or conveying under this
License, you may add to a covered work material governed by the terms
of that license document, provided that the further restriction does
not survive such relicensing or conveying.

If you add terms to a covered work in accord with this section, you
must place, in the relevant source files, a statement of the
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where to find the applicable terms.

Additional terms, permissive or non-permissive, may be stated in the
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above requirements apply either way.

@item Termination.

You may not propagate or modify a covered work except as expressly
provided under this License.  Any attempt otherwise to propagate or
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this License (including any patent licenses granted under the third
paragraph of section 11).

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, you do not qualify to receive new licenses for the same
material under section 10.

@item Acceptance Not Required for Having Copies.

You are not required to accept this License in order to receive or run
a copy of the Program.  Ancillary propagation of a covered work
occurring solely as a consequence of using peer-to-peer transmission
to receive a copy likewise does not require acceptance.  However,
nothing other than this License grants you permission to propagate or
modify any covered work.  These actions infringe copyright if you do
not accept this License.  Therefore, by modifying or propagating a
covered work, you indicate your acceptance of this License to do so.

@item Automatic Licensing of Downstream Recipients.

Each time you convey a covered work, the recipient automatically
receives a license from the original licensors, to run, modify and
propagate that work, subject to this License.  You are not responsible
for enforcing compliance by third parties with this License.

An ``entity transaction'' is a transaction transferring control of an
organization, or substantially all assets of one, or subdividing an
organization, or merging organizations.  If propagation of a covered
work results from an entity transaction, each party to that
transaction who receives a copy of the work also receives whatever
licenses to the work the party's predecessor in interest had or could
give under the previous paragraph, plus a right to possession of the
Corresponding Source of the work from the predecessor in interest, if
the predecessor has it or can get it with reasonable efforts.

You may not impose any further restrictions on the exercise of the
rights granted or affirmed under this License.  For example, you may
not impose a license fee, royalty, or other charge for exercise of
rights granted under this License, and you may not initiate litigation
(including a cross-claim or counterclaim in a lawsuit) alleging that
any patent claim is infringed by making, using, selling, offering for
sale, or importing the Program or any portion of it.

@item Patents.

A ``contributor'' is a copyright holder who authorizes use under this
License of the Program or a work on which the Program is based.  The
work thus licensed is called the contributor's ``contributor version''.

A contributor's ``essential patent claims'' are all patent claims owned
or controlled by the contributor, whether already acquired or
hereafter acquired, that would be infringed by some manner, permitted
by this License, of making, using, or selling its contributor version,
but do not include claims that would be infringed only as a
consequence of further modification of the contributor version.  For
purposes of this definition, ``control'' includes the right to grant
patent sublicenses in a manner consistent with the requirements of
this License.

Each contributor grants you a non-exclusive, worldwide, royalty-free
patent license under the contributor's essential patent claims, to
make, use, sell, offer for sale, import and otherwise run, modify and
propagate the contents of its contributor version.

In the following three paragraphs, a ``patent license'' is any express
agreement or commitment, however denominated, not to enforce a patent
(such as an express permission to practice a patent or covenant not to
sue for patent infringement).  To ``grant'' such a patent license to a
party means to make such an agreement or commitment not to enforce a
patent against the party.

If you convey a covered work, knowingly relying on a patent license,
and the Corresponding Source of the work is not available for anyone
to copy, free of charge and under the terms of this License, through a
publicly available network server or other readily accessible means,
then you must either (1) cause the Corresponding Source to be so
available, or (2) arrange to deprive yourself of the benefit of the
patent license for this particular work, or (3) arrange, in a manner
consistent with the requirements of this License, to extend the patent
license to downstream recipients.  ``Knowingly relying'' means you have
actual knowledge that, but for the patent license, your conveying the
covered work in a country, or your recipient's use of the covered work
in a country, would infringe one or more identifiable patents in that
country that you have reason to believe are valid.

If, pursuant to or in connection with a single transaction or
arrangement, you convey, or propagate by procuring conveyance of, a
covered work, and grant a patent license to some of the parties
receiving the covered work authorizing them to use, propagate, modify
or convey a specific copy of the covered work, then the patent license
you grant is automatically extended to all recipients of the covered
work and works based on it.

A patent license is ``discriminatory'' if it does not include within the
scope of its coverage, prohibits the exercise of, or is conditioned on
the non-exercise of one or more of the rights that are specifically
granted under this License.  You may not convey a covered work if you
are a party to an arrangement with a third party that is in the
business of distributing software, under which you make payment to the
third party based on the extent of your activity of conveying the
work, and under which the third party grants, to any of the parties
who would receive the covered work from you, a discriminatory patent
license (a) in connection with copies of the covered work conveyed by
you (or copies made from those copies), or (b) primarily for and in
connection with specific products or compilations that contain the
covered work, unless you entered into that arrangement, or that patent
license was granted, prior to 28 March 2007.

Nothing in this License shall be construed as excluding or limiting
any implied license or other defenses to infringement that may
otherwise be available to you under applicable patent law.

@item No Surrender of Others' Freedom.

If conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot convey
a covered work so as to satisfy simultaneously your obligations under
this License and any other pertinent obligations, then as a
consequence you may not convey it at all.  For example, if you agree
to terms that obligate you to collect a royalty for further conveying
from those to whom you convey the Program, the only way you could
satisfy both those terms and this License would be to refrain entirely
from conveying the Program.

@item Use with the GNU Affero General Public License.

Notwithstanding any other provision of this License, you have
permission to link or combine any covered work with a work licensed
under version 3 of the GNU Affero General Public License into a single
combined work, and to convey the resulting work.  The terms of this
License will continue to apply to the part which is the covered work,
but the special requirements of the GNU Affero General Public License,
section 13, concerning interaction through a network will apply to the
combination as such.

@item Revised Versions of this License.

The Free Software Foundation may publish revised and/or new versions
of the GNU General Public 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.

Each version is given a distinguishing version number.  If the Program
specifies that a certain numbered version of the GNU General Public
License ``or any later version'' applies to it, you have the option of
following the terms and conditions either of that numbered version or
of any later version published by the Free Software Foundation.  If
the Program does not specify a version number of the GNU General
Public License, you may choose any version ever published by the Free
Software Foundation.

If the Program specifies that a proxy can decide which future versions
of the GNU General Public License can be used, that proxy's public
statement of acceptance of a version permanently authorizes you to
choose that version for the Program.

Later license versions may give you additional or different
permissions.  However, no additional obligations are imposed on any
author or copyright holder as a result of your choosing to follow a
later version.

@item Disclaimer of Warranty.

THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
APPLICABLE LAW@.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM ``AS IS'' WITHOUT
WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE@.  THE ENTIRE RISK AS TO THE QUALITY AND
PERFORMANCE OF THE PROGRAM IS WITH YOU@.  SHOULD THE PROGRAM PROVE
DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR
CORRECTION.

@item Limitation of Liability.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR
CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT
NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR
LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM
TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER
PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

@item Interpretation of Sections 15 and 16.

If the disclaimer of warranty and limitation of liability provided
above cannot be given local legal effect according to their terms,
reviewing courts shall apply local law that most closely approximates
an absolute waiver of all civil liability in connection with the
Program, unless a warranty or assumption of liability accompanies a
copy of the Program in return for a fee.

@end enumerate

@heading END OF TERMS AND CONDITIONS

@heading How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least
the ``copyright'' line and a pointer to where the full notice is found.

@smallexample
@var{one line to give the program's name and a brief idea of what it does.}
Copyright (C) @var{year} @var{name of author}

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE@.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see @url{https://www.gnu.org/licenses/}.
@end smallexample

Also add information on how to contact you by electronic and paper mail.

If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:

@smallexample
@var{program} Copyright (C) @var{year} @var{name of author}
This program comes with ABSOLUTELY NO WARRANTY; for details type @samp{show w}.
This is free software, and you are welcome to redistribute it
under certain conditions; type @samp{show c} for details.
@end smallexample

The hypothetical commands @samp{show w} and @samp{show c} should show
the appropriate parts of the General Public License.  Of course, your
program's commands might be different; for a GUI interface, you would
use an ``about box''.

You should also get your employer (if you work as a programmer) or school,
if any, to sign a ``copyright disclaimer'' for the program, if necessary.
For more information on this, and how to apply and follow the GNU GPL, see
@url{https://www.gnu.org/licenses/}.

The GNU General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use
the GNU Lesser General Public License instead of this License.  But
first, please read @url{https://www.gnu.org/licenses/why-not-lgpl.html}.

@node Index,  , GNU General Public License, Top
@unnumbered Index

@printindex cp

@bye