New hint: autotools.txt

elko elko at elkos.linuxfromscratch.org
Mon Jul 15 08:57:17 PDT 2002


I've written a short introduction on using the GNU-autotools.

It is attached to this message,
please let me know what you think of it.

--
elko
-------------- next part --------------
TITLE:		GNU-Autotools
LFS-VERSION:	LFS-CVS-20011206+
AUTHOR:		Elko Holl <elko at home.nl> <elko at cyberspace.org>

SYNOPSIS:	Short introduction to the GNU autotools.

HINT:

$Id: autotools.txt,v 1.4 2002/07/15 15:22:44 elko Exp $

Contents
--------

  * Preface
  * Versions
  * Creating the source file(s)
  * Adapting configure.in
  * Creating config.h.in
  * Creating Makefile.am and Makefile.in
  * Creating the configure script
  * Testing the result
  * Making a distribution
  * Related documents
  * Warranty


Preface
-------

  Ok, so you have your BLFS finished and have all the applications you can
  think of installed. Now what? You start to learn BaSH, Perl, C and kernel
  internals and finally, you code up some cool program which you think is
  worth uploading to http://sourceforge.net for example.

  But how are you going to distribute your program? Just pack everything in
  a tarball and present a Makefile to your users that they have to modify? NO!
  You want your project to be like all the packages you already installed, so
  that means having a configure script so you can at least specify the
  installation --prefix for your program.

  With the GNU range of applications this means using autoconf and automake,
  rather then coding the required files yourself; these programs are part of
  the GNU-autotools collection.

  Here is a quote from the autoconf manual:

  "Autoconf is a tool for producing shell scripts that automatically configure
  software source code packages to adapt to many kinds of UNIX-like systems.
  The configuration scripts produced by Autoconf are independent of Autoconf
  when they are run, so their users do not need to have Autoconf."

  This document describes the minimal steps you must take to start a project
  in GNU fashion. You'll learn to use autoconf and automake to create
  configure scripts and Makefiles, almost automagically;
  just like the Pro's do it!

  For more information on autoconf and automake skip to the section at the
  bottom titled "Related documents".

  It is assumed that you already know a bit about writing a Makefile. If this
  is not the case, then first read-up on Makefiles at:

        http://www.gnu.org/manual/make/

  Hint: You can use Makefiles for more then C-program compilation, you can for
        example create targets for commonly used functions (shell-scripts). If
        this doesn't ring a bell right now, read the make-manual and it will
        start to make sense (i.e. `make backup' for your system operators).


Versions
--------

  The versions of autoconf and automake used in this document are:

  [elko at elkos ~]$ (autoconf -V;automake --version)2>&1|grep "^auto"
  autoconf (GNU Autoconf) 2.52
  automake (GNU automake) 1.6.1

  Note that as stated in the LFS-book, this newer version of autoconf
  (and automake) may cause some not so up-to-date applications to fail to
  compile on your system. You can always downgrade autoconf or automake; so if
  you experience any problems building certain packages after upgrading to the
  versions used in document, try to downgrade before complaining somewhere.

  If you are happy with your autoconf and automake release, and don't want to
  upgrade, then this document can still be used as a quick guide to start a
  project; some of the semantics may differ though, consult the documentation
  of your release for the details.


Creating the source file(s)
---------------------------

  This document only uses one source file, since it's just a quick guide to
  start a GNU fashion project. In almost any situation. your project will
  have more then one source file, that is why it is assumed that you know how
  to write Makefiles, since more sourcefiles mean more described dependencies
  in your 'Makefile.am'; more on that later, read along or skip to the section
  called "Related documents" (at the bottom) and get your information there.

  First, create a directory where you start your project and create the famous
  "Hello World!" source-file (a slightly altered version though):

cd $HOME && mkdir hello && cd hello &&
cat >hello.c <<EOHF
/*
 * hello.c example for the autotools.txt hint
 *
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <unistd.h>

int main()
{
        fprintf (stdout, "Hello World!\n");

#ifdef _WITH_GOODBYE
        sleep (1);
        fprintf (stdout, "Goodbye Cruel World!\n");
#endif

        return (0);
}
EOHF

  Note that there are some header-files included and there is a symbol
  definition check present to change the behavior of the program. This is
  done on purpose to show some details of the autotools; almost every project
  you create will have conditionals in the source to enhance or alter the
  behavior of your software. The #ifdef and #ifndef statements play an
  important part in your flexibility with the GNU-autotools.

  The next step is to create the 'config.h' file, which autoscan uses to
  create the input file for autoheader:

cat >config.h <<EOHF
#define VERSION=1.0
EOHF


Adapting configure.in
---------------------

  Now that you have your source-file(s) in place, you have to create a file
  for autoconf - which describes your project - called 'configure.in'.
  To generate a template for this file, you can use `autoscan', which will
  create a file named 'configure.scan'; rename that file to 'configure.in':

autoscan &&
mv configure.scan configure.in

  You have to adapt 'configure.in' for your project now. In this example,
  it is modified as follows (some blank lines removed):

  -[snip]-
  # Process this file with autoconf to produce a configure script.
  # - Change program presets
  AC_INIT(hello, 1.0, elko at home.nl)
  AC_CONFIG_SRCDIR([hello.c])
  # - Change AC to AM (automake version)
  AM_CONFIG_HEADER([config.h])

  # - Add this line for a bzip2 dist
  AM_INIT_AUTOMAKE(dist-bzip2)

  # - The following lines adds the --enable-goodbye option to configure:
  #
  # Give the user the choice to enter one of these:
  # --enable-goodbye
  # --enable-goodbye=yes
  # --enable-goodbye=no
  #
  AC_MSG_CHECKING([whether we are enabling goodbye])
  AC_ARG_ENABLE(goodbye,
        AC_HELP_STRING([--enable-goodbye], [Say goodbye as well]),
        [if test "${enable_goodbye}" = "yes" ; then
                AC_DEFINE(_WITH_GOODBYE, 1, Say goodbye as well)
                AC_MSG_RESULT([yes])
        else
                AC_DEFINE(_WITH_GOODBYE, 0, Say goodbye as well)
                AC_MSG_RESULT([no])
        fi],
        # Default value for configure
        AC_MSG_RESULT([no])
        )

  # Checks for programs.
  AC_PROG_CC
  # Checks for libraries.
  # Checks for header files.

  # Automatically added by autoscan
  AC_CHECK_HEADERS([unistd.h])

  # - The following line demonstrates checking for header files yourself:
  #
  # do nothing if stdio.h is found, else print an error
  AC_CHECK_HEADER(stdio.h, , AC_MSG_ERROR([stdio.h not found!]))

  # Checks for typedefs, structures, and compiler characteristics.
  # Checks for library functions.

  # - Add Makefile
  AC_CONFIG_FILES([Makefile])
  AC_OUTPUT
  -[snip]-

  The 'AM_INIT_AUTOMAKE' is specified because I wish to have a make target
  called 'dist-bzip2', which makes a bzipped tarball from my development tree.
  AC in the AC_CONFIG_HEADER is changed to AM because the version of automake
  used in this document prefers it over the AC prefix.

  For other options you can specify in the 'configure.in' file, skip to the
  section "Related documents" at the bottom of this document.


Creating aclocal.m4
-------------------

  In order for autoconf and automake to recognize and translate defined
  macro's, you have to run `aclocal', which generates the 'aclocal.m4'
  macro-file:

aclocal


Creating config.h.in
--------------------

  This file is required by automake because you created a 'config.h' file,
  so just run `autoheader' and your done:

autoheader


Creating Makefile.am and Makefile.in
------------------------------------

  Now you need a way to specify the rules which make must follow. The syntax
  of a 'Makefile.am' (AutoMake) almost resembles that of an ordinary Makefile,
  in this example, you create the 'Makefile.am' like this:

cat >Makefile.am 2>/dev/null <<EOHF
bin_PROGRAMS = hello

CC = @CC@
program:
        $(CC) -o hello hello.c     # <-- this line starts with a TAB!
#
EOHF

  The 'Makefile.am' file is used to generate a 'Makefile.in', that is used by
  the configure script, which enables the user of your package to specify
  system specifics that will be reflected in the final (real) Makefile.

  Once you have 'Makefile.am', you can run `automake' to create 'Makefile.in'.
  If you do so at this moment however, it will complain about missing files,
  which are normally part of a standard "GNU-package". These files are:

        install-sh, mkinstalldirs, missing, ChangeLog, depcomp,
        INSTALL, NEWS, README, COPYING, AUTHORS.

  However, automake provides an option to add those missing files
  (in case they are found on your system) if you add the -a flag
  to automake (short for --add-missing). So let's do that:

automake --add-missing

  The output of this command looks something like:

        configure.in: installing `./install-sh'
        configure.in: installing `./mkinstalldirs'
        configure.in: installing `./missing'
        Makefile.am: installing `./INSTALL'
        Makefile.am: required file `./NEWS' not found
        Makefile.am: required file `./README' not found
        Makefile.am: installing `./COPYING'
        Makefile.am: required file `./AUTHORS' not found
        Makefile.am: required file `./ChangeLog' not found
        Makefile.am: installing `./depcomp'

  Some symbolic links will be created in your project directory, pointing
  to the various locations where the files are found. As you can see,
  some files are still missing: NEWS, README, AUTHORS and ChangeLog.

  If you want those files to also be installed when you add the -a flag
  to automake, create those files in the same place where the symlinks
  point to.

  The missing files are just informal ones. It's up to you to decide if
  you want them, though it isn't a bad idea to follow the GNU convention
  and execute the following command to create the missing files:

touch NEWS README AUTHORS ChangeLog

  Run `automake' again to verify it isn't complaining anymore:

automake

  In case you are wondering, the symbolic links will be replaced by the
  programs themselves if you do a `make dist' when you are ready to
  distribute your project, read along.


Creating the configure script
-----------------------------

  To create the configure script, just run `autoconf' and you're done:

autoconf


Testing the result
------------------

  Before you test the result, it is always a good idea to backup your work:

cd .. &&
cp -a hello hello.ok &&
cd -

  Now test if the configure script works as expected; while testing, pay
  close attention to the output that you get from the configure script,
  especially the '--enable-goodbye' option and the 'stdio.h' check:

./configure --prefix=$HOME/hello-test \
        --bindir=$HOME/hello-test &&
make &&
make install

  See if the program works:

ls -l ../hello-test &&
../hello-test/hello

  Now test if our configure-option gets recognized:

./configure --prefix=$HOME/hello-test\
        --bindir=$HOME/hello-test \
        --enable-goodbye &&
make &&
make install

  And again, see if the program works:

./hello &&
../hello-test/hello

  If you execute a `make uninstall', you will notice the binary is removed,
  but the directory is still there; this is a good thing, because if you
  installed the package in /usr/bin for example, you wouldn't want the
  uninstall rule to `rm -fr' your entire /usr/bin as well.

  You could enhance the Makefile to test for an empty directory and then
  remove it, or just add a `rmdir --i <prefix>', which will quietly fail
  if the directory is not empty.


Making a distribution
---------------------

  It is possible to create a tarball from your project by executing:

make dist

  In this example you would end up with a file called "hello-1.0.tar.gz",
  and a file "hello-1.0.tar.bz2" since the target has dependencies, check
  what the package contains:

tar tvzf hello-1.0.tar.gz

  If you would only like a bzipped tarball, execute:

make dist-bzip2 &&
ls -l hello-1.0.tar.bz2 &&
tar tvjf hello-1.0.tar.bz2

  Hint: If you install "bash_completion" (available on http://freshmeat.net),
        then you can get all available make targets by entering 'make ' and
        pressing TAB twice (notice the space after the `make' command!). With
        bash_completion, the same is true for `./configure --<TAB><TAB>',
        which will list the available configure options; very neat indeed!

  To end the foolishness of making a GNU package of a 326 byte hello.c
  sourcefile, unpack the distribution you just made and see that it is
  258048 bytes now; that is ~791.56 times bigger then the original sourcefile:

tar xjf hello-1.0.tar.bz2 &&
du -sb hello-1.0

  But it is supposed to be portable now.


Related documents
-----------------

  For a full description and all the macros's you can use, visit:

        http://www.gnu.org/manual/make/
        http://www.gnu.org/manual/autoconf/
        http://www.gnu.org/manual/automake/

  For information about installing the autotools, see Linuxfromscratch:

        http://www.linuxfromscratch.org/view/cvs/chapter06/make.html
        http://www.linuxfromscratch.org/view/cvs/chapter06/autoconf.html
        http://www.linuxfromscratch.org/view/cvs/chapter06/automake.html

  I recommend reading this as well:

        http://sources.redhat.com/autobook/autobook/autobook_toc.html


Warranty
--------

  Read http://www.gnu.org/licenses/gpl.txt, section 11
  (at the time of this writing).

  If you have any questions or suggestions about this document,
  please contact the author.

  Copyleft - $Date: 2002/07/15 15:22:44 $



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