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@node Invoking gnulib-tool
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@chapter Invoking gnulib-tool
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@c Copyright (C) 2005, 2006, 2007 Free Software Foundation, Inc.
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@c Permission is granted to copy, distribute and/or modify this document
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@c under the terms of the GNU Free Documentation License, Version 1.2 or
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@c any later version published by the Free Software Foundation; with no
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@c Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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@c Texts. A copy of the license is included in the ``GNU Free
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@c Documentation License'' file as part of this distribution.
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@cindex invoking @command{gnulib-tool}
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The @command{gnulib-tool} command is the recommended way to import
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Gnulib modules. It is possible to borrow Gnulib modules in a package
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without using @command{gnulib-tool}, relying only on the
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meta-information stored in the @file{modules/*} files, but with a
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growing number of modules this becomes tedious. @command{gnulib-tool}
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simplifies the management of source files, @file{Makefile.am}s and
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@file{configure.ac} in packages incorporating Gnulib modules.
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Run @samp{gnulib-tool --help} for information. To get familiar with
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@command{gnulib-tool} without affecting your sources, you can also try
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some commands with the option @samp{--dry-run}; then
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@code{gnulib-tool} will only report which actions it would perform in
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a real run without changing anything.
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* Initial import:: First import of Gnulib modules.
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* Modified imports:: Changing the import specification.
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* Simple update:: Tracking Gnulib development.
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* CVS Issues:: Integration with CVS.
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@section Initial import
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@cindex initial import
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Gnulib assumes your project uses Autoconf and Automake. Invoking
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@samp{gnulib-tool --import} will copy source files, create a
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@file{Makefile.am} to build them, generate a file @file{gnulib-comp.m4} with
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Autoconf M4 macro declarations used by @file{configure.ac}, and generate
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a file @file{gnulib-cache.m4} containing the cached specification of how
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Our example will be a library that uses Autoconf, Automake and
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Libtool. It calls @code{strdup}, and you wish to use gnulib to make
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the package portable to C89 and C99 (which don't have @code{strdup}).
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~/src/libfoo$ gnulib-tool --import strdup
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Module list with included dependencies:
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Creating directory ./lib
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Creating directory ./m4
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Copying file lib/dummy.c
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Copying file lib/strdup.c
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Copying file lib/string_.h
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Copying file m4/absolute-header.m4
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Copying file m4/extensions.m4
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Copying file m4/gnulib-common.m4
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Copying file m4/gnulib-tool.m4
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Copying file m4/strdup.m4
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Copying file m4/string_h.m4
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Creating lib/Makefile.am
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Creating m4/gnulib-cache.m4
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Creating m4/gnulib-comp.m4
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You may need to add #include directives for the following .h files.
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- add "lib/Makefile" to AC_CONFIG_FILES in ./configure.ac,
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- mention "lib" in SUBDIRS in Makefile.am,
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- mention "-I m4" in ACLOCAL_AMFLAGS in Makefile.am,
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- invoke gl_EARLY in ./configure.ac, right after AC_PROG_CC,
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- invoke gl_INIT in ./configure.ac.
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By default, the source code is copied into @file{lib/} and the M4
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macros in @file{m4/}. You can override these paths by using
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@code{--source-base=DIRECTORY} and @code{--m4-base=DIRECTORY}. Some
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modules also provide other files necessary for building. These files
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are copied into the directory specified by @samp{AC_CONFIG_AUX_DIR} in
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@file{configure.ac} or by the @code{--aux-dir=DIRECTORY} option. If
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neither is specified, the current directory is assumed.
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@code{gnulib-tool} can make symbolic links instead of copying the
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source files. The option to specify for this is @samp{--symlink}, or
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@samp{-s} for short. This can be useful to save a few kilobytes of disk
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space. But it is likely to introduce bugs when @code{gnulib} is updated;
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it is more reliable to use @samp{gnulib-tool --update} (see below)
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to update to newer versions of @code{gnulib}. Furthermore it requires
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extra effort to create self-contained tarballs, and it may disturb some
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mechanism the maintainer applies to the sources. For these reasons,
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this option is generally discouraged.
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@code{gnulib-tool} will overwrite any pre-existing files, in
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particular @file{Makefile.am}. Unfortunately, separating the
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generated @file{Makefile.am} content (for building the gnulib library)
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into a separate file, say @file{gnulib.mk}, that could be included
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by your handwritten @file{Makefile.am} is not possible, due to how
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variable assignments are handled by Automake.
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Consequently, it is a good idea to choose directories that are not
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already used by your projects, to separate gnulib imported files from
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your own files. This approach is also useful if you want to avoid
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conflicts between other tools (e.g., @code{gettextize} that also copy
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M4 files into your package. Simon Josefsson successfully uses a source
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base of @file{gl/}, and a M4 base of @file{gl/m4/}, in several
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After the @samp{--import} option on the command line comes the list of
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Gnulib modules that you want to incorporate in your package. The names
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of the modules coincide with the filenames in Gnulib's @file{modules/}
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Some Gnulib modules depend on other Gnulib modules. @code{gnulib-tool}
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will automatically add the needed modules as well; you need not list
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them explicitly. @code{gnulib-tool} will also memorize which dependent
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modules it has added, so that when someday a dependency is dropped, the
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implicitly added module is dropped as well (unless you have explicitly
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requested that module).
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If you want to cut a dependency, i.e., not add a module although one of
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your requested modules depends on it, you may use the option
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@samp{--avoid=@var{module}} to do so. Multiple uses of this option are
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possible. Of course, you will then need to implement the same interface
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as the removed module.
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A few manual steps are required to finish the initial import.
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@code{gnulib-tool} printed a summary of these steps.
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First, you must ensure Autoconf can find the macro definitions in
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@file{gnulib-comp.m4}. Use the @code{ACLOCAL_AMFLAGS} specifier in
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your top-level @file{Makefile.am} file, as in:
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ACLOCAL_AMFLAGS = -I m4
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You are now ready to call the M4 macros in @code{gnulib-comp.m4} from
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@file{configure.ac}. The macro @code{gl_EARLY} must be called as soon
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as possible after verifying that the C compiler is working.
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Typically, this is immediately after @code{AC_PROG_CC}, as in:
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The core part of the gnulib checks are done by the macro
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@code{gl_INIT}. Place it further down in the file, typically where
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you normally check for header files or functions. It must come after
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other checks which may affect the compiler invocation, such as
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@code{AC_MINIX}. For example:
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@code{gl_INIT} will in turn call the macros related with the
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gnulib functions, be it specific gnulib macros, like @code{gl_FUNC_ALLOCA}
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or autoconf or automake macros like @code{AC_FUNC_ALLOCA} or
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@code{AM_FUNC_GETLINE}. So there is no need to call those macros yourself
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when you use the corresponding gnulib modules.
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You must also make sure that the gnulib library is built. Add the
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@code{Makefile} in the gnulib source base directory to
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@code{AC_CONFIG_FILES}, as in:
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AC_CONFIG_FILES(... lib/Makefile ...)
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You must also make sure that @code{make} will recurse into the gnulib
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directory. To achieve this, add the gnulib source base directory to a
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@code{SUBDIRS} Makefile.am statement, as in:
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or if you, more likely, already have a few entries in @code{SUBDIRS},
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you can add something like:
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Finally, you have to add compiler and linker flags in the appropriate
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source directories, so that you can make use of the gnulib library.
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Since some modules (@samp{getopt}, for example) may copy files into
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the build directory, @file{top_builddir/lib} is needed as well
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as @file{top_srcdir/lib}. For example:
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AM_CPPFLAGS = -I$(top_srcdir)/lib -I$(top_builddir)/lib
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Don't forget to @code{#include} the various header files. In this
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example, you would need to make sure that @samp{#include <string.h>}
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is evaluated when compiling all source code files, that want to make
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use of @code{strdup}.
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In the usual case where Autoconf is creating a @file{config.h} file,
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you should include @file{config.h} first, before any other include
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file. That way, for example, if @file{config.h} defines
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@samp{restrict} to be the empty string on a pre-C99 host, or a macro
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like @samp{_FILE_OFFSET_BITS} that affects the layout of data
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structures, the definition is consistent for all include files.
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Also, on some platforms macros like @samp{_FILE_OFFSET_BITS} and
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@samp{_GNU_SOURCE} may be ineffective, or may have only a limited
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effect, if defined after the first system header file is included.
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A final word of warning: Gnulib currently assumes it will be
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responsible for @emph{all} functions that end up in the Autoconf
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@code{@@LIBOBJS@@} variables (and/or @code{@@LTLIBOBJS@@} if using
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Libtool), e.g., those specified in @code{AC_REPLACE_FUNCS} in your
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@file{configure.ac}. Therefore, if you have any functions which are
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not covered by Gnulib which need that treatment, you have to
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essentially reimplement AC_REPLACE_FUNCS using different names; for an
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example, see the Findutils sources. Perhaps this will be improved in
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@node Modified imports
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@section Modified imports
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You can at any moment decide to use Gnulib differently than the last time.
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If you only want to use more Gnulib modules, simply invoke
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@command{gnulib-tool --import @var{new-modules}}. @code{gnulib-tool}
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remembers which modules were used last time. The list of modules that
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you pass after @samp{--import} is @emph{added} to the previous list of
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For most changes, such as added or removed modules, or even different
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choices of @samp{--lib}, @samp{--source-base} or @samp{--aux-dir}, there
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are two ways to perform the change.
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The standard way is to modify manually the file @file{gnulib-cache.m4}
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in the M4 macros directory, then launch @samp{gnulib-tool --import}.
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The other way is to call @command{gnulib-tool} again, with the changed
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command-line options. Note that this doesn't let you remove modules,
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because as you just learned, the list of modules is always cumulated.
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Also this way is often impractical, because you don't remember the way
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you invoked @code{gnulib-tool} last time.
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The only change for which this doesn't work is a change of the
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@samp{--m4-base} directory. Because, when you pass a different value of
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@samp{--m4-base}, @code{gnulib-tool} will not find the previous
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@file{gnulib-cache.m4} file any more... A possible solution is to manually
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copy the @file{gnulib-cache.m4} into the new M4 macro directory.
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In the @file{gnulib-cache.m4}, the macros have the following meaning:
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The argument is a space separated list of the requested modules, not including
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The argument is a space separated list of modules that should not be used,
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even if they occur as dependencies. Corresponds to the @samp{--avoid}
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command line argument.
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The argument is the relative file name of the directory containing the gnulib
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source files (mostly *.c and *.h files). Corresponds to the
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@samp{--source-base} command line argument.
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The argument is the relative file name of the directory containing the gnulib
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M4 macros (*.m4 files). Corresponds to the @samp{--m4-base} command line
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The argument is the relative file name of the directory containing the gnulib
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unit test files. Corresponds to the @samp{--tests-base} command line argument.
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The argument is the name of the library to be created. Corresponds to the
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@samp{--lib} command line argument.
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The presence of this macro corresponds to the @samp{--lgpl} command line
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argument. It takes no arguments.
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The presence of this macro corresponds to the @samp{--libtool} command line
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argument and to the absence of the @samp{--no-libtool} command line argument.
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It takes no arguments.
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@item gl_MACRO_PREFIX
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The argument is the prefix to use for macros in the @file{gnulib-comp.m4}
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file. Corresponds to the @samp{--macro-prefix} command line argument.
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@section Simple update
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When you want to update to a more recent version of Gnulib, without
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changing the list of modules or other parameters, a simple call
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$ gnulib-tool --import
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This will create, update or remove files, as needed.
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All files created by @code{gnulib-tool}, except @file{gnulib-cache.m4},
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should be treated like generated source files, like for example a
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@file{parser.c} file is generated from @file{parser.y}.
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In projects which commit all source files, whether generated or not, into
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CVS, the @code{gnulib-tool} generated files should all be committed.
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Gnulib also contains files generated by @command{make} (and removed by
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@code{make clean}), using information determined by @command{configure}
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They should not be checked into CVS, but instead added to
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@file{.cvsignore}. When you have a Gnulib source file of the form
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@file{lib/foo_.h}, the corresponding @file{lib/foo.h} is such a file.
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In projects which customarily omit from the CVS all files that generated
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from other source files, all these files and directories would not be
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added into CVS. The only file that must be added to CVS is
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@file{gnulib-cache.m4} in the M4 macros directory. Also, the script for
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restoring files not in CVS, customarily called @file{autogen.sh} or
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@file{bootstrap.sh}, will typically contain the statement for restoring
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$ gnulib-tool --update
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The @samp{--update} option operates much like the @samp{--import} option,
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but it does not offer the possibility to change the way Gnulib is used.
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Also it does not report in the ChangeLogs the files that it had to add
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because they were missing.
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The same holds for other version control systems than CVS, such as @samp{git}
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gnulib/doc/gnulib-tool.texi
