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+@node Invoking gnulib-tool
+@chapter Invoking gnulib-tool
+
+@pindex gnulib-tool
+@cindex invoking @command{gnulib-tool}
+
+@command{gnulib-tool} is the way to import Gnulib modules.  It is also
+possible to borrow Gnulib modules in a package without using
+@command{gnulib-tool}, relying only on the metainformation stored in
+the @file{modules/*} files, but with a growing number of modules this
+becomes tedious.  @command{gnulib-tool} simplifies the management of
+source files, @file{Makefile.am}s and @file{configure.ac} in packages
+incorporating Gnulib modules.
+
+Run @samp{gnulib-tool --help}.  To get familiar with @command{gnulib-tool},
+you can also try some commands with the option @samp{--dry-run}; then
+@code{gnulib-tool} will only report which actions it would perform in a
+real run.
+
+@menu
+* Initial import::              First import of Gnulib modules.
+* Modified imports::            Changing the import specification.
+* Simple update::               Tracking Gnulib development.
+* CVS Issues::                  Integration with CVS.
+@end menu
+
+
+@node Initial import
+@section Initial import
+@cindex initial import
+
+Gnulib assumes your project uses Autoconf and Automake.  Invoking
+@samp{gnulib-tool --import} will copy source files, create a
+@file{Makefile.am} to build them, generate a file @file{gnulib-comp.m4} with
+Autoconf M4 macro declarations used by @file{configure.ac}, and generate
+a file @file{gnulib-cache.m4} containing the cached specification of how
+Gnulib is used.
+
+Our example will be a library that uses Autoconf, Automake and
+Libtool.  It calls @code{strdup}, and you wish to use gnulib to make
+the package portable to C89 (which doesn't have @code{strdup}).
+
+@example
+~/src/libfoo$ gnulib-tool --import strdup
+Module list with included dependencies:
+  strdup
+File list:
+  lib/strdup.c
+  lib/strdup.h
+  m4/onceonly_2_57.m4
+  m4/strdup.m4
+Copying file m4/gnulib-tool.m4
+Copying file m4/onceonly_2_57.m4
+Copying file lib/strdup.c
+Copying file lib/strdup.h
+Copying file m4/strdup.m4
+Creating lib/Makefile.am
+Creating m4/gnulib-cache.m4
+Creating m4/gnulib-comp.m4
+Finished.
+
+You may need to add #include directives for the following .h files.
+  #include "strdup.h"
+
+Don't forget to
+  - add "lib/Makefile" to AC_CONFIG_FILES in ./configure.ac,
+  - mention "lib" in SUBDIRS in Makefile.am,
+  - mention "-I m4" in ACLOCAL_AMFLAGS in Makefile.am,
+  - invoke gl_EARLY in ./configure.ac, right after AC_PROG_CC,
+  - invoke gl_INIT in ./configure.ac.
+~/src/libfoo$
+@end example
+
+By default, the source code is copied into @file{lib/} and the M4
+macros in @file{m4/}.  You can override these paths by using
+@code{--source-base=DIRECTORY} and @code{--m4-base=DIRECTORY}.  Some
+modules also provide other files necessary for building. These files
+are copied into the directory specified by @samp{AC_CONFIG_AUX_DIR} in
+@file{configure.ac} or by the @code{--aux-dir=DIRECTORY} option.  If
+neither is specified, the current directory is assumed.
+
+@code{gnulib-tool} can make symbolic links instead of copying the
+source files.  Use the @samp{--symbolic} (or @samp{-s} for short) option
+to do this.
+
+@code{gnulib-tool} will overwrite any pre-existing files, in
+particular @file{Makefile.am}.  Unfortunately, separating the
+generated @file{Makefile.am} content (for building the gnulib library)
+into a separate file, say @file{gnulib.mk}, that could be included
+by your handwritten @file{Makefile.am} is not possible, due to how
+variable assignments are handled by Automake.
+
+Consequently, it is a good idea to choose directories that are not
+already used by your projects, to separate gnulib imported files from
+your own files.  This approach is also useful if you want to avoid
+conflicts between other tools (e.g., @code{gettextize} that also copy
+M4 files into your package.  Simon Josefsson successfully uses a source
+base of @file{gl/}, and a M4 base of @file{gl/m4/}, in several
+packages.
+
+After the @samp{--import} option on the command line comes the list of
+Gnulib modules that you want to incorporate in your package.  The names
+of the modules coincide with the filenames in Gnulib's @file{modules/}
+directory.
+
+Some Gnulib modules depend on other Gnulib modules.  @code{gnulib-tool}
+will automatically add the needed modules as well; you need not list
+them explicitly.  @code{gnulib-tool} will also memoize which dependent
+modules it has added, so that when someday a dependency is dropped, the
+implicitly added module is dropped as well (unless you have explicitly
+requested that module).
+
+If you want to cut a dependency, i.e. not add a module although one of
+your requested modules depends on it, you may use the option
+@samp{--avoid=@var{module}} to do so.  Multiple uses of this option are
+possible.  Of course, you will then need to implement the same interface
+as the removed module.
+
+A few manual steps are required to finish the initial import.
+@code{gnulib-tool} printed a summary of these steps.
+
+First, you need to make sure Autoconf can find the macro definitions
+in @file{gnulib-comp.m4}.  Use the @code{ACLOCAL_AMFLAGS} specifier in your
+top-level @file{Makefile.am} file, as in:
+
+@example
+ACLOCAL_AMFLAGS = -I m4
+@end example
+
+You are now ready to call the M4 macros in @code{gnulib-comp.m4} from
+@file{configure.ac}.  The macro @code{gl_EARLY} must be called as soon
+as possible after verifying that the C compiler is working.
+Typically, this is immediately after @code{AC_PROG_CC}, as in:
+
+@example
+...
+AC_PROG_CC
+gl_EARLY
+...
+@end example
+
+The core part of the gnulib checks are done by the macro
+@code{gl_INIT}.  Place it further down in the file, typically where
+you normally check for header files or functions.  For example:
+
+@example
+...
+# For gnulib.
+gl_INIT
+...
+@end example
+
+@code{gl_INIT} will in turn call the macros related with the
+gnulib functions, be it specific gnulib macros, like @code{gl_FUNC_ALLOCA}
+or autoconf or automake macros like @code{AC_FUNC_ALLOCA} or
+@code{AM_FUNC_GETLINE}.  So there is no need to call those macros yourself
+when you use the corresponding gnulib modules.
+
+You must also make sure that the gnulib library is built.  Add the
+@code{Makefile} in the gnulib source base directory to
+@code{AC_CONFIG_FILES}, as in:
+
+@example
+AC_CONFIG_FILES(... lib/Makefile ...)
+@end example
+
+You must also make sure that @code{make} will recurse into the gnulib
+directory.  To achieve this, add the gnulib source base directory to a
+@code{SUBDIRS} Makefile.am statement, as in:
+
+@example
+SUBDIRS = lib
+@end example
+
+or if you, more likely, already have a few entries in @code{SUBDIRS},
+you can add something like:
+
+@example
+SUBDIRS += lib
+@end example
+
+Finally, you have to add compiler and linker flags in the appropriate
+source directories, so that you can make use of the gnulib library.
+Since some modules (@samp{getopt}, for example) may copy files into
+the build directory, @file{top_builddir/lib} is needed as well
+as @file{top_srcdir/lib}.  For example:
+
+@example
+...
+AM_CPPFLAGS = -I$(top_srcdir)/lib -I$(top_builddir)/lib
+...
+LIBADD = lib/libgnu.a
+...
+@end example
+
+Don't forget to @code{#include} the various header files.  In this
+example, you would need to make sure that @samp{#include "strdup.h"}
+is evaluated when compiling all source code files, that want to make
+use of @code{strdup}.
+
+When an include file is provided by Gnulib
+you shouldn't try to include the corresponding system header files
+yourself, but let the gnulib header file do it.  The ordering
+of the definition for some symbols may be significant; the Gnulib
+header files take care of that.
+
+For example, to use the @code{time_r} gnulib module you should
+use include header file provided by the gnulib, and so
+@samp{#include "time_r.h"}, but you shouldn't explicitly
+@samp{#include <time.h>} as it is already done in @file{time_r.h}
+before the redefinition of some symbols.
+
+@node Modified imports
+@section Modified imports
+
+You can at any moment decide to use Gnulib differently than the last time.
+
+If you only want to use more Gnulib modules, simply invoke
+@command{gnulib-tool --import @var{new-modules}}.  @code{gnulib-tool}
+remembers which modules were used last time.  The list of modules that
+you pass after @samp{--import} is @emph{added} to the previous list of
+modules.
+
+For most changes, such as added or removed modules, or even different
+choices of @samp{--lib}, @samp{--source-base} or @samp{--aux-dir}, there
+are two ways to perform the change.
+
+The standard way is to modify manually the file @file{gnulib-cache.m4}
+in the M4 macros directory, then launch @samp{gnulib-tool --import}.
+
+The other way is to call @command{gnulib-tool} again, with the changed
+command-line options.  Note that this doesn't let you remove modules,
+because as you just learned, the list of modules is always cumulated.
+Also this way is often impractical, because you don't remember the way
+you invoked @code{gnulib-tool} last time.
+
+The only change for which this doesn't work is a change of the
+@samp{--m4-base} directory.  Because, when you pass a different value of
+@samp{--m4-base}, @code{gnulib-tool} will not find the previous
+@file{gnulib-cache.m4} file any more... A possible solution is to manually
+copy the @file{gnulib-cache.m4} into the new M4 macro directory.
+
+In the @file{gnulib-cache.m4}, the macros have the following meaning:
+@table @code
+@item gl_MODULES
+The argument is a space separated list of the requested modules, not including
+dependencies.
+
+@item gl_AVOID
+The argument is a space separated list of modules that should not be used,
+even if they occur as dependencies.  Corresponds to the @samp{--avoid}
+command line argument.
+
+@item gl_SOURCE_BASE
+The argument is the relative pathname of the directory containing the gnulib
+source files (mostly *.c and *.h files).  Corresponds to the
+@samp{--source-base} command line argument.
+
+@item gl_M4_BASE
+The argument is the relative pathname of the directory containing the gnulib
+M4 macros (*.m4 files).  Corresponds to the @samp{--m4-base} command line
+argument.
+
+@item gl_TESTS_BASE
+The argument is the relative pathname of the directory containing the gnulib
+unit test files.  Corresponds to the @samp{--tests-base} command line argument.
+
+@item gl_LIB
+The argument is the name of the library to be created.  Corresponds to the
+@samp{--lib} command line argument.
+
+@item gl_LGPL
+The presence of this macro corresponds to the @samp{--lgpl} command line
+argument.  It takes no arguments.
+
+@item gl_LIBTOOL
+The presence of this macro corresponds to the @samp{--libtool} command line
+argument.  It takes no arguments.
+
+@item gl_MACRO_PREFIX
+The argument is the prefix to use for macros in the @file{gnulib-comp.m4}
+file.  Corresponds to the @samp{--macro-prefix} command line argument.
+@end table
+
+@node Simple update
+@section Simple update
+
+When you want to update to a more recent version of Gnulib, without
+changing the list of modules or other parameters, a simple call
+does it:
+
+@smallexample
+$ gnulib-tool --import
+@end smallexample
+
+This will create, update or remove files, as needed.
+
+@node CVS Issues
+@section CVS Issues
+
+All files created by @code{gnulib-tool}, except @file{gnulib-cache.m4},
+should be treated like generated source files, like for example a
+@file{parser.c} file is generated from @file{parser.y}.
+
+In projects which commit all source files, whether generated or not, into
+CVS, the @code{gnulib-tool} generated files should all be committed.
+
+In projects which customarily omit from the CVS all files that generated
+from other source files, all these files and directories would not be
+added into CVS.  The only file that must be added to CVS is
+@file{gnulib-cache.m4} in the M4 macros directory.  Also, the script for
+restoring files not in CVS, customarily called @file{autogen.sh} or
+@file{bootstrap.sh}, will typically contain the statement for restoring
+the omitted files:
+
+@smallexample
+$ gnulib-tool --update
+@end smallexample
+
+The @samp{--update} option operates much like the @samp{--import} option,
+but it does not offer the possibility to change the way Gnulib is used.
+Also it does not report in the ChangeLogs the files that it had to add
+because they were missing.