Generate Makefile new version.

2.4 A Small Hello World

In this section we recreate the amhello-1.0 package fromscratch. The first subsection shows how to call the Autotools toinstantiate the GNU Build System, while the second explains themeaning of the configure.ac and Makefile.am files readby the Autotools.

• Creating amhello:		Create amhello-1.0.tar.gz from scratch
• amhello's configure.ac Setup Explained:
• amhello's Makefile.am Setup Explained:

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Next: amhello's configure.ac Setup Explained, Up: Hello World   [Contents][Index]

2.4.1 Creating amhello-1.0.tar.gz

Here is how we can recreate amhello-1.0.tar.gz from scratch.The package is simple enough so that we will only need to write 5files. (You may copy them from the final amhello-1.0.tar.gzthat is distributed with Automake if you do not want to write them.)

Create the following files in an empty directory.

• src/main.c is the source file for the hello program. Westore it in the src/ subdirectory, because later, when the packageevolves, it will ease the addition of a man/ directory for manpages, a data/ directory for data files, etc.

  ~/amhello % cat src/main.c
  #include 
  #include 
  
  int
  main (void)
  {
    puts ("Hello World!");
    puts ("This is " PACKAGE_STRING ".");
    return 0;
  }
  

• README contains some very limited documentation for our littlepackage.

  ~/amhello % cat README
  This is a demonstration package for GNU Automake.
  Type 'info Automake' to read the Automake manual.
  

• Makefile.am and src/Makefile.am contain Automakeinstructions for these two directories.

  ~/amhello % cat src/Makefile.am
  bin_PROGRAMS = hello
  hello_SOURCES = main.c
  ~/amhello % cat Makefile.am
  SUBDIRS = src
  dist_doc_DATA = README
  

• Finally, configure.ac contains Autoconf instructions tocreate the configure script.

  ~/amhello % cat configure.ac
  AC_INIT([amhello], [1.0], [[email protected]])
  AM_INIT_AUTOMAKE([-Wall -Werror foreign])
  AC_PROG_CC
  AC_CONFIG_HEADERS([config.h])
  AC_CONFIG_FILES([
   Makefile
   src/Makefile
  ])
  AC_OUTPUT
  

Once you have these five files, it is time to run the Autotools toinstantiate the build system. Do this using the autoreconfcommand as follows:

~/amhello % autoreconf --install
configure.ac: installing './install-sh'
configure.ac: installing './missing'
configure.ac: installing './compile'
src/Makefile.am: installing './depcomp'

At this point the build system is complete.

In addition to the three scripts mentioned in its output, you can seethat autoreconf created four other files: configure,config.h.in, Makefile.in, and src/Makefile.in.The latter three files are templates that will be adapted to thesystem by configure under the names config.h,Makefile, and src/Makefile. Let’s do this:

~/amhello % ./configure
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for gawk... no
checking for mawk... mawk
checking whether make sets $(MAKE)... yes
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking for style of include used by make... GNU
checking dependency style of gcc... gcc3
configure: creating ./config.status
config.status: creating Makefile
config.status: creating src/Makefile
config.status: creating config.h
config.status: executing depfiles commands

You can see Makefile, src/Makefile, and config.hbeing created at the end after configure has probed thesystem. It is now possible to run all the targets we wish(see Standard Targets). For instance:

~/amhello % make
…
~/amhello % src/hello
Hello World!
This is amhello 1.0.
~/amhello % make distcheck
…
=============================================
amhello-1.0 archives ready for distribution:
amhello-1.0.tar.gz
=============================================

Note that running autoreconf is only needed initially whenthe GNU Build System does not exist. When you later change someinstructions in a Makefile.am or configure.ac, therelevant part of the build system will be regenerated automaticallywhen you execute make.