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The following sections cover a few basic ideas that will help you understand how Automake works.
Automake works by reading a `Makefile.am' and generating a `Makefile.in'. Certain macros and targets defined in the `Makefile.am' instruct Automake to generate more specialized code; for instance, a `bin_PROGRAMS' macro definition will cause targets for compiling and linking programs to be generated.
The macro definitions and targets in the `Makefile.am' are copied
verbatim into the generated file. This allows you to add arbitrary code
into the generated `Makefile.in'. For instance the Automake
distribution includes a non-standard cvs-dist target, which the
Automake maintainer uses to make distributions from his source control
system.
Note that GNU make extensions are not recognized by Automake. Using such extensions in a `Makefile.am' will lead to errors or confusing behavior.
Automake tries to group comments with adjoining targets and macro definitions in an intelligent way.
A target defined in `Makefile.am' generally overrides any such
target of a similar name that would be automatically generated by
automake. Although this is a supported feature, it is generally
best to avoid making use of it, as sometimes the generated rules are
very particular.
Similarly, a macro defined in `Makefile.am' will override any
definition of the macro that automake would ordinarily create.
This feature is more often useful than the ability to override a target
definition. Be warned that many of the macros generated by
automake are considered to be for internal use only, and their
names might change in future releases.
When examining a macro definition, Automake will recursively examine
macros referenced in the definition. For example, if Automake is
looking at the content of foo_SOURCES in this snippet
xs = a.c b.c foo_SOURCES = c.c $(xs)
it would use the files `a.c', `b.c', and `c.c' as the
contents of foo_SOURCES.
Automake also allows a form of comment which is not copied into the output; all lines beginning with `##' are completely ignored by Automake.
It is customary to make the first line of `Makefile.am' read:
## Process this file with automake to produce Makefile.in
automake supports three kinds of directory hierarchy:
`flat', `shallow', and `deep'.
A flat package is one in which all the files are in a single
directory. The `Makefile.am' for such a package by definition
lacks a SUBDIRS macro. An example of such a package is
termutils.
A deep package is one in which all the source lies in
subdirectories; the top level directory contains mainly configuration
information. GNU cpio is a good example of such a package, as is
GNU tar. The top level `Makefile.am' for a deep package
will contain a SUBDIRS macro, but no other macros to define
objects which are built.
A shallow package is one in which the primary source resides in
the top-level directory, while various parts (typically libraries)
reside in subdirectories. Automake is one such package (as is GNU
make, which does not currently use automake).
While Automake is intended to be used by maintainers of GNU packages, it does make some effort to accommodate those who wish to use it, but do not want to use all the GNU conventions.
To this end, Automake supports three levels of strictness---the strictness indicating how stringently Automake should check standards conformance.
The valid strictness levels are:
For more information on the precise implications of the strictness
level, see section The effect of --gnu and --gnits.
Automake macros (from here on referred to as variables) generally
follow a uniform naming scheme that makes it easy to decide how
programs (and other derived objects) are built, and how they are
installed. This scheme also supports configure time
determination of what should be built.
At make time, certain variables are used to determine which
objects are to be built. These variables are called primary
variables. For instance, the primary variable PROGRAMS holds a
list of programs which are to be compiled and linked.
A different set of variables is used to decide where the built objects
should be installed. These variables are named after the primary
variables, but have a prefix indicating which standard directory should
be used as the installation directory. The standard directory names are
given in the GNU standards (see section `Directory Variables' in The GNU Coding Standards). Automake extends this list with
pkglibdir, pkgincludedir, and pkgdatadir; these are
the same as the non-`pkg' versions, but with `@PACKAGE@'
appended. For instance, pkglibdir is defined as
$(datadir)/@PACKAGE@.
For each primary, there is one additional variable named by prepending
`EXTRA_' to the primary name. This variable is used to list
objects which may or may not be built, depending on what
configure decides. This variable is required because Automake
must statically know the entire list of objects that may be built in
order to generate a `Makefile.in' that will work in all cases.
For instance, cpio decides at configure time which programs are
built. Some of the programs are installed in bindir, and some
are installed in sbindir:
EXTRA_PROGRAMS = mt rmt bin_PROGRAMS = cpio pax sbin_PROGRAMS = @PROGRAMS@
Defining a primary variable without a prefix (e.g. PROGRAMS) is
an error.
Note that the common `dir' suffix is left off when constructing the variable names; thus one writes `bin_PROGRAMS' and not `bindir_PROGRAMS'.
Not every sort of object can be installed in every directory. Automake will flag those attempts it finds in error. Automake will also diagnose obvious misspellings in directory names.
Sometimes the standard directories--even as augmented by Automake---
are not enough. In particular it is sometimes useful, for clarity, to
install objects in a subdirectory of some predefined directory. To this
end, Automake allows you to extend the list of possible installation
directories. A given prefix (e.g. `zar') is valid if a variable of
the same name with `dir' appended is defined (e.g. zardir).
For instance, until HTML support is part of Automake, you could use this to install raw HTML documentation:
htmldir = $(prefix)/html html_DATA = automake.html
The special prefix `noinst' indicates that the objects in question should not be installed at all.
The special prefix `check' indicates that the objects in question
should not be built until the make check command is run.
Possible primary names are `PROGRAMS', `LIBRARIES', `LISP', `SCRIPTS', `DATA', `HEADERS', `MANS', and `TEXINFOS'.
Sometimes a Makefile variable name is derived from some text the user
supplies. For instance, program names are rewritten into Makefile macro
names. Automake canonicalizes this text, so that it does not have to
follow Makefile macro naming rules. All characters in the name except
for letters, numbers, and the underscore are turned into underscores
when making macro references. For example, if your program is named
sniff-glue, the derived variable name would be
sniff_glue_SOURCES, not sniff-glue_SOURCES.
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