amhello’s Makefile.am Setup Explained ¶We now turn to src/Makefile.am. This file contains Automake instructions to build and install hello.
bin_PROGRAMS = hello hello_SOURCES = main.c
A Makefile.am has the same syntax as an ordinary
Makefile. When automake processes a
Makefile.am it copies the entire file into the output
Makefile.in (that will be later turned into Makefile by
configure) but will react to certain variable definitions
by generating some build rules and other variables.
Often Makefile.ams contain only a list of variable definitions as
above, but they can also contain other variable and rule definitions that
automake will pass along without interpretation.
Variables that end with _PROGRAMS are special variables
that list programs that the resulting Makefile should build.
In Automake speak, this _PROGRAMS suffix is called a
primary; Automake recognizes other primaries such as
_SCRIPTS, _DATA, _LIBRARIES, etc. corresponding
to different types of files.
The ‘bin’ part of the bin_PROGRAMS tells
automake that the resulting programs should be installed in
bindir. Recall that the GNU Build System uses a set of variables
to denote destination directories and allow users to customize these
locations (see Standard Directory Variables). Any such directory
variable can be put in front of a primary (omitting the dir
suffix) to tell automake where to install the listed files.
Programs need to be built from source files, so for each program
prog listed in a _PROGRAMS variable,
automake will look for another variable named
prog_SOURCES listing its source files. There may be more
than one source file: they will all be compiled and linked together.
Automake also knows that source files need to be distributed when
creating a tarball (unlike built programs). So a side-effect of this
hello_SOURCES declaration is that main.c will be
part of the tarball created by make dist.
Finally here are some explanations regarding the top-level Makefile.am.
SUBDIRS = src dist_doc_DATA = README
SUBDIRS is a special variable listing all directories that
make should recurse into before processing the current
directory. So this line is responsible for make building
src/hello even though we run it from the top-level. This line
also causes make install to install src/hello before
installing README (not that this order matters).
The line dist_doc_DATA = README causes README to be
distributed and installed in docdir. Files listed with the
_DATA primary are not automatically part of the tarball built
with make dist, so we add the dist_ prefix so they get
distributed. However, for README it would not have been
necessary: automake automatically distributes any
README file it encounters (the list of other files
automatically distributed is presented by automake --help).
The only important effect of this second line is therefore to install
README during make install.
One thing not covered in this example is accessing the installation directory values (see Standard Directory Variables) from your program code, that is, converting them into defined macros. For this, see Defining Directories in The Autoconf Manual.