https://www.gnu.org/software/automake/manual/automake.html#Hello-World
info Automake
to read the automake manual
autoreconf --install
./configure
make
./src/hello # to run the executable
To distribute software for build from source,
first run the autoreconf --install which will initialize the GNU Build system.
then a user should ./configure, make, make check, su, make install,
make installcheck.
autoreconf creates configure, config.h.in, Makefile.in, src/Makefile.in
the latter three files are templates that will be adapted to system
by configure under names config.h, Makefile, and src/Makefile
autoreconf calls autoconf, automake and other commands in a certain order
autoconf creates configure from configure.ac,
automake creates Makefile.ins from Makefile.ams and configure.ac
configure.ac is read by autoconf and automake.
It contains M4 macros that will be expanded to form configure script.
(see "Writing configure.ac" in the Autoconf Manual)
AC_* are autoconf macros (see autoconf macro index),
and AM_* are automake macros (see automake macro index)
argument to AM_INIT_AUTOMAKE is list of options for automake
(see options in manual).
-Wall and -Werror turns on all Automake warnings and reports as errors.
(e.g. incorrect instructions in Makefile.am).
foreign tells Automake that this package will not follow GNU Standards
(e.g. ChangeLog, AUTHORS, etc.)
AC_PROG_CC causes configure script to search for a C compiler, and define
the CC variable with its name.
src/Makefile.in gen'd by Automake uses this CC var to build hello,
so when configure creates src/Makefile from src/Makefile.in
it will define CC with val it has found.
AC_CONFIG_HEADERS([config.h]) causes configure to create config.h
which gathers #define's defined by other macros in configure.ac
(e.g. PACKAGE_BUGREPORT and PACKAGE_STRING).
In an actual project, config.h can contain one define per feature probed on system.
AC_CONFIG_FILES declares list of files that configure should create from
*.in templates.
Automake also scans this list to find Makefile.am files it must process.
(important) when adding new directory to proj, add its Makefile to this list.
otherwise Automake will not process the new Makefile.am you wrote in that dir.
Finally, AC_OUTPUT is a closing command that produces part of script in charge
of creating files registerd with AC_CONFIG_HEADERS and AC_CONFIG_FILES
When starting a new project, start with simple configure.ac and
gradually add other tests(?) it requires.
autoscan can suggest a few tests that package may need.
(see Using autoscan to create configure.ac in autoconf man)
has same syntax as ordinary makefile.
*_PROGRAMS suffix to variables is called a primary.
other primaries include _SCRIPTS, _DATA, _LIBRARIES...
bin in bin_PROGRAMAS means hello should be installed in the bindir
hello.c will be included in a tarball created by make dist.
SUBDIRS lists directories that make should recurse into before process
current dir.
it also causes src/hello to be installed with make install before
README.md
dist_doc_DATA causes the readme to be distributed and installed in docdir
Not covered here is accessing install directory valies (See standard dir variables) from program code. i.e. converting them into defined macros (Defining directories) in automake manual