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 <bobg+stow@@zanshin.com>
@*
@copyright{} 2000, 2001 Guillaume Morin <gmorin@@gnu.org>
@*
@copyright{} 2007 Kahlil (Kal) Hodgson <kahlil@@internode.on.net>
@*
@copyright{} 2011 Adam Spiers <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 Univerity, Australia.
@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

@ifinfo
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 ifinfo
@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.  A common, but by no
means the only such location is @file{/usr/local}.  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.

@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.

@cindex symlink
@cindex relative symlink
@cindex absolute symlink
A @dfn{symlink} is a symbolic link.  A symlink can be @dfn{relative} or
@dfn{absolute}.  An absolute symlink names a full path; that is, one
starting from @file{/}.  A relative symlink names a relative path; that
is, one not starting from @file{/}.  The target of a relative symlink is
computed starting from the symlink's own directory.  Stow only
creates relative symlinks.

@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.

@item --no-folding

This disables any further @ref{tree folding} or @ref{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 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 effectively prepended to the command line arguments
(with the notable difference that they won't be processed by the shell).
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.


@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

Please send bug reports to the current maintainers by electronic
mail.  The address to use is @samp{<bug-stow@@gnu.org>}.  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=3} 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.

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

There are no known bugs in Stow version @value{VERSION}!
If you think you have found one, please @pxref{Reporting Bugs}.

@c @itemize @bullet
@c @item
@c Put known bugs here
@c @end itemize

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

@center Version 2, June 1991

@display
Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
675 Mass Ave, Cambridge, MA 02139, USA

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

@unnumberedsec Preamble

  The licenses for most software are designed to take away your
freedom to share and change it.  By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software---to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  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
this service 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 free programs; and that you know you can do these things.

  To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

  For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

  We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

  Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

  Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

  The precise terms and conditions for copying, distribution and
modification follow.

@iftex
@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
@end iftex
@ifinfo
@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
@end ifinfo

@enumerate 0
@item
This License applies to any program or other work which contains
a notice placed by the copyright holder saying it may be distributed
under the terms of this General Public License.  The ``Program'', below,
refers to any such program or work, and a ``work based on the Program''
means either the Program or any derivative work under copyright law:
that is to say, a work containing the Program or a portion of it,
either verbatim or with modifications and/or translated into another
language.  (Hereinafter, translation is included without limitation in
the term ``modification''.)  Each licensee is addressed as ``you''.

Activities other than copying, distribution and modification are not
covered by this License; they are outside its scope.  The act of
running the Program is not restricted, and the output from the Program
is covered only if its contents constitute a work based on the
Program (independent of having been made by running the Program).
Whether that is true depends on what the Program does.

@item
You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an appropriate
copyright notice and disclaimer of warranty; keep intact all the
notices that refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of this License
along with the Program.

You may charge a fee for the physical act of transferring a copy, and
you may at your option offer warranty protection in exchange for a fee.

@item
You may modify your copy or copies of the Program or any portion
of it, thus forming a work based on the Program, and copy and
distribute such modifications or work under the terms of Section 1
above, provided that you also meet all of these conditions:

@enumerate a
@item
You must cause the modified files to carry prominent notices
stating that you changed the files and the date of any change.

@item
You must cause any work that you distribute or publish, that in
whole or in part contains or is derived from the Program or any
part thereof, to be licensed as a whole at no charge to all third
parties under the terms of this License.

@item
If the modified program normally reads commands interactively
when run, you must cause it, when started running for such
interactive use in the most ordinary way, to print or display an
announcement including an appropriate copyright notice and a
notice that there is no warranty (or else, saying that you provide
a warranty) and that users may redistribute the program under
these conditions, and telling the user how to view a copy of this
License.  (Exception: if the Program itself is interactive but
does not normally print such an announcement, your work based on
the Program is not required to print an announcement.)
@end enumerate

These requirements apply to the modified work as a whole.  If
identifiable sections of that work are not derived from the Program,
and can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works.  But when you
distribute the same sections as part of a whole which is a work based
on the Program, the distribution of the whole must be on the terms of
this License, whose permissions for other licensees extend to the
entire whole, and thus to each and every part regardless of who wrote it.

Thus, it is not the intent of this section to claim rights or contest
your rights to work written entirely by you; rather, the intent is to
exercise the right to control the distribution of derivative or
collective works based on the Program.

In addition, mere aggregation of another work not based on the Program
with the Program (or with a work based on the Program) on a volume of
a storage or distribution medium does not bring the other work under
the scope of this License.

@item
You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:

@enumerate a
@item
Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of Sections
1 and 2 above on a medium customarily used for software interchange; or,

@item
Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than your
cost of physically performing source distribution, a complete
machine-readable copy of the corresponding source code, to be
distributed under the terms of Sections 1 and 2 above on a medium
customarily used for software interchange; or,

@item
Accompany it with the information you received as to the offer
to distribute corresponding source code.  (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form with such
an offer, in accord with Subsection b above.)
@end enumerate

The source code for a work means the preferred form of the work for
making modifications to it.  For an executable work, complete source
code means all the source code for all modules it contains, plus any
associated interface definition files, plus the scripts used to
control compilation and installation of the executable.  However, as a
special exception, the source code distributed need not include
anything that is normally distributed (in either source or binary
form) with the major components (compiler, kernel, and so on) of the
operating system on which the executable runs, unless that component
itself accompanies the executable.

If distribution of executable or object code is made by offering
access to copy from a designated place, then offering equivalent
access to copy the source code from the same place counts as
distribution of the source code, even though third parties are not
compelled to copy the source along with the object code.

@item
You may not copy, modify, sublicense, or distribute the Program
except as expressly provided under this License.  Any attempt
otherwise to copy, modify, sublicense or distribute the Program 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.

@item
You are not required to accept this License, since you have not
signed it.  However, nothing else grants you permission to modify or
distribute the Program or its derivative works.  These actions are
prohibited by law if you do not accept this License.  Therefore, by
modifying or distributing the Program (or any work based on the
Program), you indicate your acceptance of this License to do so, and
all its terms and conditions for copying, distributing or modifying
the Program or works based on it.

@item
Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program subject to
these terms and conditions.  You may not impose any further
restrictions on the recipients' exercise of the rights granted herein.
You are not responsible for enforcing compliance by third parties to
this License.

@item
If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent issues),
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
distribute so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you
may not distribute the Program at all.  For example, if a patent
license would not permit royalty-free redistribution of the Program by
all those who receive copies directly or indirectly through you, then
the only way you could satisfy both it and this License would be to
refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under
any particular circumstance, the balance of the section is intended to
apply and the section as a whole is intended to apply in other
circumstances.

It is not the purpose of this section to induce you to infringe any
patents or other property right claims or to contest validity of any
such claims; this section has the sole purpose of protecting the
integrity of the free software distribution system, which is
implemented by public license practices.  Many people have made
generous contributions to the wide range of software distributed
through that system in reliance on consistent application of that
system; it is up to the author/donor to decide if he or she is willing
to distribute software through any other system and a licensee cannot
impose that choice.

This section is intended to make thoroughly clear what is believed to
be a consequence of the rest of this License.

@item
If the distribution and/or use of the Program is restricted in
certain countries either by patents or by copyrighted interfaces, the
original copyright holder who places the Program under this License
may add an explicit geographical distribution limitation excluding
those countries, so that distribution is permitted only in or among
countries not thus excluded.  In such case, this License incorporates
the limitation as if written in the body of this License.

@item
The Free Software Foundation may publish revised and/or new versions
of the 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 a version number of this License which applies to it and ``any
later version'', you have the option of following the terms and conditions
either of that version or of any later version published by the Free
Software Foundation.  If the Program does not specify a version number of
this License, you may choose any version ever published by the Free Software
Foundation.

@item
If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the author
to ask for permission.  For software which is copyrighted by the Free
Software Foundation, write to the Free Software Foundation; we sometimes
make exceptions for this.  Our decision will be guided by the two goals
of preserving the free status of all derivatives of our free software and
of promoting the sharing and reuse of software generally.

@iftex
@heading NO WARRANTY
@end iftex
@ifinfo
@center NO WARRANTY
@end ifinfo

@item
BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, 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
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE 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.
@end enumerate

@iftex
@heading END OF TERMS AND CONDITIONS
@end iftex
@ifinfo
@center END OF TERMS AND CONDITIONS
@end ifinfo

@page
@unnumberedsec 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
convey 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 an idea of what it does.}
Copyright (C) 19@var{yy}  @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 2
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, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
@end smallexample

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

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

@smallexample
Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author}
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'.  This is free software, and you are welcome
to redistribute it under certain conditions; type `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, the
commands you use may be called something other than @samp{show w} and
@samp{show c}; they could even be mouse-clicks or menu items---whatever
suits your program.

You should also get your employer (if you work as a programmer) or your
school, if any, to sign a ``copyright disclaimer'' for the program, if
necessary.  Here is a sample; alter the names:

@smallexample
@group
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written
by James Hacker.

@var{signature of Ty Coon}, 1 April 1989
Ty Coon, President of Vice
@end group
@end smallexample

This 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 Library
General Public License instead of this License.

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

@printindex cp

@bye