2.1 General Operation

Automake works by reading a Makefile.am and generating a Makefile.in. Certain variables and rules defined in the Makefile.am instruct Automake to generate more specialized code; for instance, a ‘bin_PROGRAMS’ variable definition will cause rules for compiling and linking programs to be generated.

The variable definitions and rules 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 rule for the cvs-dist target, which the Automake maintainer uses to make distributions from his source control system.

Note that most GNU make extensions are not recognized by Automake. Using such extensions in a Makefile.am will lead to errors or confusing behavior.

A special exception is that the GNU make append operator, ‘+=’, is supported. This operator appends its right hand argument to the variable specified on the left. Automake will translate the operator into an ordinary ‘=’ operator; ‘+=’ will thus work with any make program.

Automake tries to keep comments grouped with any adjoining rules or variable definitions.

A rule defined in Makefile.am generally overrides any such rule 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 variable defined in Makefile.am or AC_SUBST’ed from configure.ac will override any definition of the variable that automake would ordinarily create. This feature is more often useful than the ability to override a rule. Be warned that many of the variables generated by automake are considered to be for internal use only, and their names might change in future releases.

When examining a variable definition, Automake will recursively examine variables 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 ‘##’ (leading spaces allowed) 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

2.2 Strictness

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:

‘foreign’

Automake will check for only those things which are absolutely required for proper operations. For instance, whereas GNU standards dictate the existence of a NEWS file, it will not be required in this mode. The name comes from the fact that Automake is intended to be used for GNU programs; these relaxed rules are not the standard mode of operation.

‘gnu’

Automake will check—as much as possible—for compliance to the GNU standards for packages. This is the default.

‘gnits’

Automake will check for compliance to the as-yet-unwritten Gnits standards. These are based on the GNU standards, but are even more detailed. Unless you are a Gnits standards contributor, it is recommended that you avoid this option until such time as the Gnits standard is actually published (which may never happen).

For more information on the precise implications of the strictness level, see The effect of --gnu and --gnits.

Automake also has a special “cygnus” mode which is similar to strictness but handled differently. This mode is useful for packages which are put into a “Cygnus” style tree (e.g., the GCC tree). For more information on this mode, see The effect of --cygnus.

2.3 The Uniform Naming Scheme

Automake 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. The variable names are made of several pieces which are concatenated together.

The piece which tells automake what is being built is commonly called the primary. For instance, the primary PROGRAMS holds a list of programs which are to be compiled and linked.

A different set of names is used to decide where the built objects should be installed. These names are prefixes to the primary which indicate which standard directory should be used as the installation directory. The standard directory names are given in the GNU standards (see 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 $(libdir)/$(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 = $(MORE_PROGRAMS)

Defining a primary without a prefix as a variable, 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, installation of HTML files 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 be built but not installed at all. This is usually used for objects required to build the rest of your package, for instance static libraries (see Building a library), or helper scripts.

The special prefix ‘check’ indicates that the objects in question should not be built until the make check command is run. Those objects are not installed either.

The current primary names are ‘PROGRAMS’, ‘LIBRARIES’, ‘LISP’, ‘PYTHON’, ‘JAVA’, ‘SCRIPTS’, ‘DATA’, ‘HEADERS’, ‘MANS’, and ‘TEXINFOS’.

Some primaries also allow additional prefixes which control other aspects of automake’s behavior. The currently defined prefixes are ‘dist_’, ‘nodist_’, and ‘nobase_’. These prefixes are explained later (see Program and Library Variables).

2.4 How derived variables are named

Sometimes a Makefile variable name is derived from some text the maintainer supplies. For instance, a program name listed in ‘_PROGRAMS’ is rewritten into the name of a ‘_SOURCES’ variable. In cases like this, Automake canonicalizes the text, so that program names and the like do not have to follow Makefile variable naming rules. All characters in the name except for letters, numbers, the strudel (@), and the underscore are turned into underscores when making variable references.

For example, if your program is named sniff-glue, the derived variable name would be sniff_glue_SOURCES, not sniff-glue_SOURCES. Similarly the sources for a library named libmumble++.a should be listed in the libmumble___a_SOURCES variable.

The strudel is an addition, to make the use of Autoconf substitutions in variable names less obfuscating.

2.5 Variables reserved for the user

Some Makefile variables are reserved by the GNU Coding Standards for the use of the “user” – the person building the package. For instance, CFLAGS is one such variable.

Sometimes package developers are tempted to set user variables such as CFLAGS because it appears to make their job easier. However, the package itself should never set a user variable, particularly not to include switches which are required for proper compilation of the package. Since these variables are documented as being for the package builder, that person rightfully expects to be able to override any of these variables at build time.

To get around this problem, automake introduces an automake-specific shadow variable for each user flag variable. (Shadow variables are not introduced for variables like CC, where they would make no sense.) The shadow variable is named by prepending ‘AM_’ to the user variable’s name. For instance, the shadow variable for YFLAGS is AM_YFLAGS.

2.6 Programs automake might require

Automake sometimes requires helper programs so that the generated Makefile can do its work properly. There are a fairly large number of them, and we list them here.

ansi2knr.c

ansi2knr.1

These two files are used by the automatic de-ANSI-fication support (see Automatic de-ANSI-fication).

compile

This is a wrapper for compilers which don’t accept both ‘-c’ and ‘-o’ at the same time. It is only used when absolutely required. Such compilers are rare.

config.guess

config.sub

These programs compute the canonical triplets for the given build, host, or target architecture. These programs are updated regularly to support new architectures and fix probes broken by changes in new kernel versions. You are encouraged to fetch the latest versions of these files from ftp://ftp.gnu.org/gnu/config/ before making a release.

depcomp

This program understands how to run a compiler so that it will generate not only the desired output but also dependency information which is then used by the automatic dependency tracking feature.

elisp-comp

This program is used to byte-compile Emacs Lisp code.

install-sh

This is a replacement for the install program which works on platforms where install is unavailable or unusable.

mdate-sh

This script is used to generate a version.texi file. It examines a file and prints some date information about it.

missing

This wraps a number of programs which are typically only required by maintainers. If the program in question doesn’t exist, missing prints an informative warning and attempts to fix things so that the build can continue.

mkinstalldirs

This script used to be a wrapper around mkdir -p, which is not portable. Now we use prefer to use install-sh -d when configure finds that mkdir -p does not work, this makes one less script to distribute.

For backward compatibility mkinstalldirs is still used and distributed when automake finds it in a package. But it is no longer installed automatically, and it should be safe to remove it.

py-compile

This is used to byte-compile Python scripts.

texinfo.tex

Not a program, this file is required for make dvi, make ps and make pdf to work when Texinfo sources are in the package.

ylwrap

This program wraps lex and yacc and ensures that, for instance, multiple yacc instances can be invoked in a single directory in parallel.

3.1 A simple example, start to finish

Let’s suppose you just finished writing zardoz, a program to make your head float from vortex to vortex. You’ve been using Autoconf to provide a portability framework, but your Makefile.ins have been ad-hoc. You want to make them bulletproof, so you turn to Automake.

The first step is to update your configure.ac to include the commands that automake needs. The way to do this is to add an AM_INIT_AUTOMAKE call just after AC_INIT:

AC_INIT(zardoz, 1.0)
AM_INIT_AUTOMAKE
…

Since your program doesn’t have any complicating factors (e.g., it doesn’t use gettext, it doesn’t want to build a shared library), you’re done with this part. That was easy!

Now you must regenerate configure. But to do that, you’ll need to tell autoconf how to find the new macro you’ve used. The easiest way to do this is to use the aclocal program to generate your aclocal.m4 for you. But wait… maybe you already have an aclocal.m4, because you had to write some hairy macros for your program. The aclocal program lets you put your own macros into acinclude.m4, so simply rename and then run:

mv aclocal.m4 acinclude.m4
aclocal
autoconf

Now it is time to write your Makefile.am for zardoz. Since zardoz is a user program, you want to install it where the rest of the user programs go: bindir. Additionally, zardoz has some Texinfo documentation. Your configure.ac script uses AC_REPLACE_FUNCS, so you need to link against ‘$(LIBOBJS)’. So here’s what you’d write:

bin_PROGRAMS = zardoz
zardoz_SOURCES = main.c head.c float.c vortex9.c gun.c
zardoz_LDADD = $(LIBOBJS)

info_TEXINFOS = zardoz.texi

Now you can run automake --add-missing to generate your Makefile.in and grab any auxiliary files you might need, and you’re done!

3.2 A classic program

GNU hello is renowned for its classic simplicity and versatility. This section shows how Automake could be used with the GNU Hello package. The examples below are from the latest beta version of GNU Hello, but with all of the maintainer-only code stripped out, as well as all copyright comments.

Of course, GNU Hello is somewhat more featureful than your traditional two-liner. GNU Hello is internationalized, does option processing, and has a manual and a test suite.

Here is the configure.ac from GNU Hello. Please note: The calls to AC_INIT and AM_INIT_AUTOMAKE in this example use a deprecated syntax. For the current approach, see the description of AM_INIT_AUTOMAKE in Public macros.

dnl Process this file with autoconf to produce a configure script.
AC_INIT(src/hello.c)
AM_INIT_AUTOMAKE(hello, 1.3.11)
AM_CONFIG_HEADER(config.h)

dnl Set of available languages.
ALL_LINGUAS="de fr es ko nl no pl pt sl sv"

dnl Checks for programs.
AC_PROG_CC
AC_ISC_POSIX

dnl Checks for libraries.

dnl Checks for header files.
AC_STDC_HEADERS
AC_HAVE_HEADERS(string.h fcntl.h sys/file.h sys/param.h)

dnl Checks for library functions.
AC_FUNC_ALLOCA

dnl Check for st_blksize in struct stat
AC_ST_BLKSIZE

dnl internationalization macros
AM_GNU_GETTEXT
AC_OUTPUT([Makefile doc/Makefile intl/Makefile po/Makefile.in \
           src/Makefile tests/Makefile tests/hello],
   [chmod +x tests/hello])

The ‘AM_’ macros are provided by Automake (or the Gettext library); the rest are standard Autoconf macros.

The top-level Makefile.am:

EXTRA_DIST = BUGS ChangeLog.O
SUBDIRS = doc intl po src tests

As you can see, all the work here is really done in subdirectories.

The po and intl directories are automatically generated using gettextize; they will not be discussed here.

In doc/Makefile.am we see:

info_TEXINFOS = hello.texi
hello_TEXINFOS = gpl.texi

This is sufficient to build, install, and distribute the GNU Hello manual.

Here is tests/Makefile.am:

TESTS = hello
EXTRA_DIST = hello.in testdata

The script hello is generated by configure, and is the only test case. make check will run this test.

Last we have src/Makefile.am, where all the real work is done:

bin_PROGRAMS = hello
hello_SOURCES = hello.c version.c getopt.c getopt1.c getopt.h system.h
hello_LDADD = $(INTLLIBS) $(ALLOCA)
localedir = $(datadir)/locale
INCLUDES = -I../intl -DLOCALEDIR=\"$(localedir)\"

3.3 Building true and false

Here is another, trickier example. It shows how to generate two programs (true and false) from the same source file (true.c). The difficult part is that each compilation of true.c requires different cpp flags.

bin_PROGRAMS = true false
false_SOURCES =
false_LDADD = false.o

true.o: true.c
        $(COMPILE) -DEXIT_CODE=0 -c true.c

false.o: true.c
        $(COMPILE) -DEXIT_CODE=1 -o false.o -c true.c

Note that there is no true_SOURCES definition. Automake will implicitly assume that there is a source file named true.c, and define rules to compile true.o and link true. The true.o: true.c rule supplied by the above Makefile.am, will override the Automake generated rule to build true.o.

false_SOURCES is defined to be empty—that way no implicit value is substituted. Because we have not listed the source of false, we have to tell Automake how to link the program. This is the purpose of the false_LDADD line. A false_DEPENDENCIES variable, holding the dependencies of the false target will be automatically generated by Automake from the content of false_LDADD.

The above rules won’t work if your compiler doesn’t accept both ‘-c’ and ‘-o’. The simplest fix for this is to introduce a bogus dependency (to avoid problems with a parallel make):

true.o: true.c false.o
        $(COMPILE) -DEXIT_CODE=0 -c true.c

false.o: true.c
        $(COMPILE) -DEXIT_CODE=1 -c true.c && mv true.o false.o

Also, these explicit rules do not work if the de-ANSI-fication feature is used (see Automatic de-ANSI-fication). Supporting de-ANSI-fication requires a little more work:

true_.o: true_.c false_.o
        $(COMPILE) -DEXIT_CODE=0 -c true_.c

false_.o: true_.c
        $(COMPILE) -DEXIT_CODE=1 -c true_.c && mv true_.o false_.o

As it turns out, there is also a much easier way to do this same task. Some of the above techniques are useful enough that we’ve kept the example in the manual. However if you were to build true and false in real life, you would probably use per-program compilation flags, like so:

bin_PROGRAMS = false true

false_SOURCES = true.c
false_CPPFLAGS = -DEXIT_CODE=1

true_SOURCES = true.c
true_CPPFLAGS = -DEXIT_CODE=0

In this case Automake will cause true.c to be compiled twice, with different flags. De-ANSI-fication will work automatically. In this instance, the names of the object files would be chosen by automake; they would be false-true.o and true-true.o. (The name of the object files rarely matters.)

5.1 Configuration requirements

The one real requirement of Automake is that your configure.ac call AM_INIT_AUTOMAKE. This macro does several things which are required for proper Automake operation (see Autoconf macros supplied with Automake).

Here are the other macros which Automake requires but which are not run by AM_INIT_AUTOMAKE:

AC_CONFIG_FILES

AC_OUTPUT

Automake uses these to determine which files to create (see Creating Output Files in The Autoconf Manual). A listed file is considered to be an Automake generated Makefile if there exists a file with the same name and the .am extension appended. Typically, AC_CONFIG_FILES([foo/Makefile]) will cause Automake to generate foo/Makefile.in if foo/Makefile.am exists.

When using AC_CONFIG_FILES with multiple input files, as in AC_CONFIG_FILES([Makefile:top.in:Makefile.in:bot.in]), Automake will generate the first .in input file for which a .am file exists. If no such file exists the output file is not considered to be Automake generated.

Files created by AC_CONFIG_FILES are removed by make distclean.

5.2 Other things Automake recognizes

Every time Automake is run it calls Autoconf to trace configure.ac. This way it can recognize the use of certain macros and tailor the generated Makefile.in appropriately. Currently recognized macros and their effects are:

AC_CONFIG_HEADERS

Automake will generate rules to rebuild these headers. Older versions of Automake required the use of AM_CONFIG_HEADER (see Autoconf macros supplied with Automake); this is no longer the case today.

AC_CONFIG_LINKS

Automake will generate rules to remove configure generated links on make distclean and to distribute named source files as part of make dist.

AC_CONFIG_AUX_DIR

Automake will look for various helper scripts, such as install-sh, in the directory named in this macro invocation. (The full list of scripts is: config.guess, config.sub, depcomp, elisp-comp, compile, install-sh, ltmain.sh, mdate-sh, missing, mkinstalldirs, py-compile, texinfo.tex, and ylwrap.) Not all scripts are always searched for; some scripts will only be sought if the generated Makefile.in requires them.

If AC_CONFIG_AUX_DIR is not given, the scripts are looked for in their ‘standard’ locations. For mdate-sh, texinfo.tex, and ylwrap, the standard location is the source directory corresponding to the current Makefile.am. For the rest, the standard location is the first one of ., .., or ../.. (relative to the top source directory) that provides any one of the helper scripts. See Finding ‘configure’ Input in The Autoconf Manual.

Required files from AC_CONFIG_AUX_DIR are automatically distributed, even if there is no Makefile.am in this directory.

AC_CANONICAL_BUILD

AC_CANONICAL_HOST

AC_CANONICAL_TARGET

Automake will ensure that config.guess and config.sub exist. Also, the Makefile variables ‘build_triplet’, ‘host_triplet’ and ‘target_triplet’ are introduced. See Getting the Canonical System Type in The Autoconf Manual.

AC_LIBSOURCE

AC_LIBSOURCES

AC_LIBOBJ

Automake will automatically distribute any file listed in AC_LIBSOURCE or AC_LIBSOURCES.

Note that the AC_LIBOBJ macro calls AC_LIBSOURCE. So if an Autoconf macro is documented to call AC_LIBOBJ([file]), then file.c will be distributed automatically by Automake. This encompasses many macros like AC_FUNC_ALLOCA, AC_FUNC_MEMCMP, AC_REPLACE_FUNCS, and others.

By the way, direct assignments to LIBOBJS are no longer supported. You should always use AC_LIBOBJ for this purpose. See AC_LIBOBJ vs. LIBOBJS in The Autoconf Manual.

AC_PROG_RANLIB

This is required if any libraries are built in the package. See Particular Program Checks in The Autoconf Manual.

AC_PROG_CXX

This is required if any C++ source is included. See Particular Program Checks in The Autoconf Manual.

AC_PROG_F77

This is required if any Fortran 77 source is included. This macro is distributed with Autoconf version 2.13 and later. See Particular Program Checks in The Autoconf Manual.

AC_F77_LIBRARY_LDFLAGS

This is required for programs and shared libraries that are a mixture of languages that include Fortran 77 (see Mixing Fortran 77 With C and C++). See Autoconf macros supplied with Automake.

AC_PROG_FC

This is required if any Fortran 90/95 source is included. This macro is distributed with Autoconf version 2.58 and later. See Particular Program Checks in The Autoconf Manual.

AC_PROG_LIBTOOL

Automake will turn on processing for libtool (see Introduction in The Libtool Manual).

AC_PROG_YACC

If a Yacc source file is seen, then you must either use this macro or define the variable ‘YACC’ in configure.ac. The former is preferred (see Particular Program Checks in The Autoconf Manual).

AC_PROG_LEX

If a Lex source file is seen, then this macro must be used. See Particular Program Checks in The Autoconf Manual.

AC_SUBST ¶

The first argument is automatically defined as a variable in each generated Makefile.in. See Setting Output Variables in The Autoconf Manual.

If the Autoconf manual says that a macro calls AC_SUBST for var, or defines the output variable var then var will be defined in each Makefile.in generated by Automake. E.g. AC_PATH_XTRA defines X_CFLAGS and X_LIBS, so you can use these variables in any Makefile.am if AC_PATH_XTRA is called.

AM_C_PROTOTYPES

This is required when using automatic de-ANSI-fication; see Automatic de-ANSI-fication.

AM_GNU_GETTEXT

This macro is required for packages which use GNU gettext (see Gettext). It is distributed with gettext. If Automake sees this macro it ensures that the package meets some of gettext’s requirements.

AM_MAINTAINER_MODE ¶

This macro adds a ‘--enable-maintainer-mode’ option to configure. If this is used, automake will cause ‘maintainer-only’ rules to be turned off by default in the generated Makefile.ins. This macro defines the ‘MAINTAINER_MODE’ conditional, which you can use in your own Makefile.am.

m4_include ¶

Files included by configure.ac using this macro will be detected by Automake and automatically distributed. They will also appear as dependencies in Makefile rules.

m4_include is seldom used by configure.ac authors, but can appear in aclocal.m4 when aclocal detects that some required macros come from files local to your package (as opposed to macros installed in a system-wide directory, see Auto-generating aclocal.m4).

5.3 Auto-generating aclocal.m4

Automake includes a number of Autoconf macros which can be used in your package (see Autoconf macros supplied with Automake); some of them are actually required by Automake in certain situations. These macros must be defined in your aclocal.m4; otherwise they will not be seen by autoconf.

The aclocal program will automatically generate aclocal.m4 files based on the contents of configure.ac. This provides a convenient way to get Automake-provided macros, without having to search around. The aclocal mechanism allows other packages to supply their own macros (see Writing your own aclocal macros). You can also use it to maintain your own set of custom macros (see Handling Local Macros).

At startup, aclocal scans all the .m4 files it can find, looking for macro definitions (see Macro search path). Then it scans configure.ac. Any mention of one of the macros found in the first step causes that macro, and any macros it in turn requires, to be put into aclocal.m4.

Putting the file that contains the macro definition into aclocal.m4 is usually done by copying the entire text of this file, including unused macro definitions as well as both ‘#’ and ‘dnl’ comments. If you want to make a comment which will be completely ignored by aclocal, use ‘##’ as the comment leader.

When a file selected by aclocal is located in a subdirectory specified as a relative search path with aclocal’s -I argument, aclocal assumes the file belongs to the package and uses m4_include instead of copying it into aclocal.m4. This makes the package smaller, eases dependency tracking, and cause the file to be distributed automatically. (see Handling Local Macros for an example.) Any macro which is found in a system-wide directory, or via an absolute search path will be copied. So use -I `pwd`/reldir instead of -I reldir whenever some relative directory need to be considered outside the package.

The contents of acinclude.m4, if this file exists, are also automatically included in aclocal.m4. We recommend against using acinclude.m4 in new packages (see Handling Local Macros).

While computing aclocal.m4, aclocal runs autom4te (see Using Autom4te in The Autoconf Manual) in order to trace the macros which are really used, and omit from aclocal.m4 all macros which are mentioned but otherwise unexpanded (this can happen when a macro is called conditionally). autom4te is expected to be in the PATH, just as autoconf. Its location can be overridden using the AUTOM4TE environment variable.

5.4 aclocal options

aclocal accepts the following options:

--acdir=dir ¶

Look for the macro files in dir instead of the installation directory. This is typically used for debugging.

--help ¶

Print a summary of the command line options and exit.

-I dir ¶

Add the directory dir to the list of directories searched for .m4 files.

--force ¶

Always overwrite the output file. The default is to overwrite the output file only when really needed, i.e., when its contents changes or if one of its dependencies is younger.

--output=file ¶

Cause the output to be put into file instead of aclocal.m4.

--print-ac-dir ¶

Prints the name of the directory which aclocal will search to find third-party .m4 files. When this option is given, normal processing is suppressed. This option can be used by a package to determine where to install a macro file.

--verbose ¶

Print the names of the files it examines.

--version ¶

Print the version number of Automake and exit.

5.5 Macro search path

By default, aclocal searches for .m4 files in the following directories, in this order:

acdir-APIVERSION

This is where the .m4 macros distributed with automake itself are stored. APIVERSION depends on the automake release used; for automake 1.6.x, APIVERSION = 1.6.

acdir

This directory is intended for third party .m4 files, and is configured when automake itself is built. This is @datadir@/aclocal/, which typically expands to ${prefix}/share/aclocal/. To find the compiled-in value of acdir, use the --print-ac-dir option (see aclocal options).

As an example, suppose that automake-1.6.2 was configured with --prefix=/usr/local. Then, the search path would be:

1. /usr/local/share/aclocal-1.6/
2. /usr/local/share/aclocal/

As explained in (see aclocal options), there are several options that can be used to change or extend this search path.

• Modifying the macro search path: --acdir
• Modifying the macro search path: -I dir
• Modifying the macro search path: dirlist

/test1
/test2

5.6 Autoconf macros supplied with Automake

Automake ships with several Autoconf macros that you can use from your configure.ac. When you use one of them it will be included by aclocal in aclocal.m4.

• Public macros
• Private macros

5.7 Writing your own aclocal macros

The aclocal program doesn’t have any built-in knowledge of any macros, so it is easy to extend it with your own macros.

This can be used by libraries which want to supply their own Autoconf macros for use by other programs. For instance the gettext library supplies a macro AM_GNU_GETTEXT which should be used by any package using gettext. When the library is installed, it installs this macro so that aclocal will find it.

A macro file’s name should end in .m4. Such files should be installed in $(datadir)/aclocal. This is as simple as writing:

aclocaldir = $(datadir)/aclocal
aclocal_DATA = mymacro.m4 myothermacro.m4

A file of macros should be a series of properly quoted AC_DEFUN’s (see Macro Definitions in The Autoconf Manual). The aclocal programs also understands AC_REQUIRE (see Prerequisite Macros in The Autoconf Manual), so it is safe to put each macro in a separate file. Each file should have no side effects but macro definitions. Especially, any call to AC_PREREQ should be done inside the defined macro, not at the beginning of the file.

Starting with Automake 1.8, aclocal will warn about all underquoted calls to AC_DEFUN. We realize this will annoy a lot of people, because aclocal was not so strict in the past and many third party macros are underquoted; and we have to apologize for this temporary inconvenience. The reason we have to be stricter is that a future implementation of aclocal (see The Future of aclocal) will have to temporary include all these third party .m4 files, maybe several times, even those which are not actually needed. Doing so should alleviate many problem of the current implementation, however it requires a stricter style from the macro authors. Hopefully it is easy to revise the existing macros. For instance

# bad style
AC_PREREQ(2.57)
AC_DEFUN(AX_FOOBAR,
[AC_REQUIRE([AX_SOMETHING])dnl
AX_FOO
AX_BAR
])

should be rewritten as

AC_DEFUN([AX_FOOBAR],
[AC_PREREQ(2.57)dnl
AC_REQUIRE([AX_SOMETHING])dnl
AX_FOO
AX_BAR
])

Wrapping the AC_PREREQ call inside the macro ensures that Autoconf 2.57 will not be required if AX_FOOBAR is not actually used. Most importantly, quoting the first argument of AC_DEFUN allows the macro to be redefined or included twice (otherwise this first argument would be expansed during the second definition).

If you have been directed here by the aclocal diagnostic but are not the maintainer of the implicated macro, you will want to contact the maintainer of that macro. Please make sure you have the last version of the macro and that the problem already hasn’t been reported before doing so: people tend to work faster when they aren’t flooded by mails.

Another situation where aclocal is commonly used is to manage macros which are used locally by the package, Handling Local Macros.

5.8 Handling Local Macros

Feature tests offered by Autoconf do not cover all needs. People often have to supplement existing tests with their own macros, or with third-party macros.

There are two ways to organize custom macros in a package.

The first possibility (the historical practice) is to list all your macros in acinclude.m4. This file will be included in aclocal.m4 when you run aclocal, and its macro(s) will henceforth be visible to autoconf. However if it contains numerous macros, it will rapidly become difficult to maintain, and it will be almost impossible to share macros between packages.

The second possibility, which we do recommend, is to write each macro in its own file and gather all these files in a directory. This directory is usually called m4/. To build aclocal.m4, one should therefore instruct aclocal to scan m4/. From the command line, this is done with aclocal -I m4. The top-level Makefile.am should also be updated to define

 ACLOCAL_AMFLAGS = -I m4

ACLOCAL_AMFLAGS contains options to pass to aclocal when aclocal.m4 is to be rebuilt by make. This line is also used by autoreconf (see Using autoreconf to Update configure Scripts in The Autoconf Manual) to run aclocal with suitable options, or by autopoint (see Invoking the autopoint Program in GNU gettext tools) and gettextize (see Invoking the gettextize Program in GNU gettext tools) to locate the place where Gettext’s macros should be installed. So even if you do not really care about the rebuild rules, you should define ACLOCAL_AMFLAGS.

When aclocal -I m4 is run, it will build a aclocal.m4 that m4_includes any file from m4/ that defines a required macro. Macros not found locally will still be searched in system-wide directories, as explained in Macro search path.

Custom macros should be distributed for the same reason that configure.ac is: so that other people have all the sources of your package if they want to work on it. Actually, this distribution happens automatically because all m4_included files are distributed.

However there is no consensus on the distribution of third-party macros that your package may use. Many libraries install their own macro in the system-wide aclocal directory (see Writing your own aclocal macros). For instance Guile ships with a file called guile.m4 that contains the macro GUILE_FLAGS which can be used to define setup compiler and linker flags appropriate for using Guile. Using GUILE_FLAGS in configure.ac will cause aclocal to copy guile.m4 into aclocal.m4, but as guile.m4 is not part of the project, it will not be distributed. Technically, that means a user which needs to rebuild aclocal.m4 will have to install Guile first. This is probably OK, if Guile already is a requirement to build the package. However, if Guile is only an optional feature, or if your package might run on architectures where Guile cannot be installed, this requirement will hinder development. An easy solution is to copy such third-party macros in your local m4/ directory so they get distributed.

5.9 The Future of aclocal

aclocal is expected to disappear. This feature really should not be offered by Automake. Automake should focus on generating Makefiles; dealing with M4 macros really is Autoconf’s job. That some people install Automake just to use aclocal, but do not use automake otherwise is an indication of how that feature is misplaced.

The new implementation will probably be done slightly differently. For instance it could enforce the m4/-style layout discussed in Handling Local Macros, and take care of copying (and even updating) third-party macros from /usr/share/aclocal/ into the local m4/ directory.

We have no idea when and how this will happen. This has been discussed several times in the past, but someone still has to commit itself to that non-trivial task.

From the user point of view, aclocal’s removal might turn out to be painful. There is a simple precaution that you may take to make that switch more seamless: never call aclocal yourself. Keep this guy under the exclusive control of autoreconf and Automake’s rebuild rules. Hopefully you won’t need to worry about things breaking, when aclocal disappears, because everything will have been taken care of. If otherwise you used to call aclocal directly yourself or from some script, you will quickly notice the change.

Many packages come with a script called bootstrap.sh or autogen.sh, that will just call aclocal, libtoolize, gettextize or autopoint, autoconf, autoheader, and automake in the right order. Actually this is precisely what autoreconf can do for you. If your package has such a bootstrap.sh or autogen.sh script, consider using autoreconf. That should simplify its logic a lot (less things to maintain, yum!), it’s even likely you will not need the script anymore, and more to the point you will not call aclocal directly anymore.

For the time being, third-party packages should continue to install public macros into /usr/share/aclocal/. If aclocal is replaced by another tool it might make sense to rename the directory, but supporting /usr/share/aclocal/ for backward compatibility should be really easy provided all macros are properly written (see Writing your own aclocal macros).

6.1 Recursing subdirectories

In packages with subdirectories, the top level Makefile.am must tell Automake which subdirectories are to be built. This is done via the SUBDIRS variable.

The SUBDIRS variable holds a list of subdirectories in which building of various sorts can occur. The rules for many targets (e.g. all) in the generated Makefile will run commands both locally and in all specified subdirectories. Note that the directories listed in SUBDIRS are not required to contain Makefile.ams; only Makefiles (after configuration). This allows inclusion of libraries from packages which do not use Automake (such as gettext; see also Third-Party Makefiles).

In packages that use subdirectories, the top-level Makefile.am is often very short. For instance, here is the Makefile.am from the GNU Hello distribution:

EXTRA_DIST = BUGS ChangeLog.O README-alpha
SUBDIRS = doc intl po src tests

When Automake invokes make in a subdirectory, it uses the value of the MAKE variable. It passes the value of the variable AM_MAKEFLAGS to the make invocation; this can be set in Makefile.am if there are flags you must always pass to make.

The directories mentioned in SUBDIRS are usually direct children of the current directory, each subdirectory containing its own Makefile.am with a SUBDIRS pointing to deeper subdirectories. Automake can be used to construct packages of arbitrary depth this way.

By default, Automake generates Makefiles which work depth-first in postfix order: the subdirectories are built before the current directory. However, it is possible to change this ordering. You can do this by putting ‘.’ into SUBDIRS. For instance, putting ‘.’ first will cause a ‘prefix’ ordering of directories.

Using

SUBDIRS = lib src . test

will cause lib/ to be built before src/, then the current directory will be built, finally the test/ directory will be built. It is customary to arrange test directories to be built after everything else since they are meant to test what have been constructed.

All ‘clean’ rules are run in reverse order of build rules.

6.2 Conditional Subdirectories

It is possible to define the SUBDIRS variable conditionally if, like in the case of GNU Inetutils, you want to only build a subset of the entire package.

To illustrate how this works, let’s assume we have two directories src/ and opt/. src/ should always be built, but we want to decide in ./configure whether opt/ will be built or not. (For this example we will assume that opt/ should be built when the variable $want_opt was set to yes.)

Running make should thus recurse into src/ always, and then maybe in opt/.

However make dist should always recurse into both src/ and opt/. Because opt/ should be distributed even if it is not needed in the current configuration. This means opt/Makefile should be created unconditionally.

There are two ways to setup a project like this. You can use Automake conditionals (see Conditionals) or use Autoconf AC_SUBST variables (see Setting Output Variables in The Autoconf Manual). Using Automake conditionals is the preferred solution. Before we illustrate these two possibility, let’s introduce DIST_SUBDIRS.

• SUBDIRS vs. DIST_SUBDIRS
• Conditional subdirectories with AM_CONDITIONAL
• Conditional Subdirectories with AC_SUBST
• Non-configured Subdirectories

…
AM_CONDITIONAL([COND_OPT], [test "$want_opt" = yes])
AC_CONFIG_FILES([Makefile src/Makefile opt/Makefile])
…

if COND_OPT
  MAYBE_OPT = opt
endif
SUBDIRS = src $(MAYBE_OPT)

…
if test "$want_opt" = yes; then
  MAYBE_OPT=opt
else
  MAYBE_OPT=
fi
AC_SUBST([MAYBE_OPT])
AC_CONFIG_FILES([Makefile src/Makefile opt/Makefile])
…

SUBDIRS = src $(MAYBE_OPT)
DIST_SUBDIRS = src opt

6.3 An Alternative Approach to Subdirectories

If you’ve ever read Peter Miller’s excellent paper, Recursive Make Considered Harmful, the preceding sections on the use of subdirectories will probably come as unwelcome advice. For those who haven’t read the paper, Miller’s main thesis is that recursive make invocations are both slow and error-prone.

Automake provides sufficient cross-directory support ³ to enable you to write a single Makefile.am for a complex multi-directory package.

By default an installable file specified in a subdirectory will have its directory name stripped before installation. For instance, in this example, the header file will be installed as $(includedir)/stdio.h:

include_HEADERS = inc/stdio.h

However, the ‘nobase_’ prefix can be used to circumvent this path stripping. In this example, the header file will be installed as $(includedir)/sys/types.h:

nobase_include_HEADERS = sys/types.h

‘nobase_’ should be specified first when used in conjunction with either ‘dist_’ or ‘nodist_’ (see What Goes in a Distribution). For instance:

nobase_dist_pkgdata_DATA = images/vortex.pgm

6.4 Nesting Packages

In the GNU Build System, packages can be nested to arbitrary depth. This means that a package can embedded other packages with their own configure, Makefiles, etc.

These other packages should just appear as subdirectories of their parent package. They must be listed in SUBDIRS like other ordinary directories. However the subpackage’s Makefiles should be output by its own configure script, not by the parent’s configure. This is achieved using the AC_CONFIG_SUBDIRS Autoconf macro (see Configuring Other Packages in Subdirectories in The Autoconf Manual).

Here is an example package for an arm program that links with an hand library that is a nested package in subdirectory hand/.

arm’s configure.ac:

AC_INIT([arm], [1.0])
AC_CONFIG_AUX_DIR([.])
AM_INIT_AUTOMAKE
AC_PROG_CC
AC_CONFIG_FILES([Makefile])
# Call hand's ./configure script recursively.
AC_CONFIG_SUBDIRS([hand])
AC_OUTPUT

arm’s Makefile.am:

# Build the library in the hand subdirectory first.
SUBDIRS = hand

# Include hand's header when compiling this directory.
AM_CPPFLAGS = -I$(srcdir)/hand

bin_PROGRAMS = arm
arm_SOURCES = arm.c
# link with the hand library.
arm_LDADD = hand/libhand.a

Now here is hand’s hand/configure.ac:

AC_INIT([hand], [1.2])
AC_CONFIG_AUX_DIR([.])
AM_INIT_AUTOMAKE
AC_PROG_CC
AC_PROG_RANLIB
AC_CONFIG_FILES([Makefile])
AC_OUTPUT

and its hand/Makefile.am:

lib_LIBRARIES = libhand.a
libhand_a_SOURCES = hand.c

When make dist is run from the top-level directory it will create an archive arm-1.0.tar.gz that contains the arm code as well as the hand subdirectory. This package can be built and installed like any ordinary package, with the usual ./configure && make && make install sequence (the hand subpackage will be built and installed by the process).

When make dist is run from the hand directory, it will create a self-contained hand-1.2.tar.gz archive. So although it appears to be embedded in another package, it can still be used separately.

The purpose of the AC_CONFIG_AUX_DIR([.]) instruction is to force Automake and Autoconf into search auxiliary script in the current directory. For instance this means that there will be two copies of install-sh: one in the top-level of the arm package, and another one in the hand/ subdirectory for the hand package.

The historical default is to search these auxiliary scripts in the immediate parent and grand-parent directories. So if the AC_CONFIG_AUX_DIR([.]) line was removed from hand/configure.ac, that subpackage would share the auxiliary script of the arm package. This may looks like a gain in size (a few kilobytes), but it is actually a loss of modularity as the hand subpackage is no longer self-contained (make dist in the subdirectory will not work anymore).

Packages that do not use Automake need more work to be integrated this way. See Third-Party Makefiles.

7.1 Building a program

In order to build a program, you need to tell Automake which sources are part of it, and which libraries it should be linked with.

This section also covers conditional compilation of sources or programs. Most of the comments about these also apply to libraries (see Building a library) and libtool libraries (see Building a Shared Library).

• Defining program sources
• Linking the program
• Conditional compilation of sources
• Conditional compilation of programs

bin_PROGRAMS = hello

hello_SOURCES = hello.c version.c getopt.c getopt1.c getopt.h system.h

bin_PROGRAMS = cpio pax $(MT)
libexec_PROGRAMS = $(RMT)
EXTRA_PROGRAMS = mt rmt

LDADD = ../lib/libcpio.a $(INTLLIBS)
rmt_LDADD =

cpio_SOURCES = …
pax_SOURCES = …
mt_SOURCES = …
rmt_SOURCES = …

bin_PROGRAMS = hello
hello_SOURCES = hello-common.c
EXTRA_hello_SOURCES = hello-linux.c hello-generic.c
hello_LDADD = $(HELLO_SYSTEM)
hello_DEPENDENCIES = $(HELLO_SYSTEM)

…
case $host in
  *linux*) HELLO_SYSTEM='hello-linux.$(OBJEXT)' ;;
  *)       HELLO_SYSTEM='hello-generic.$(OBJEXT)' ;;
esac
AC_SUBST([HELLO_SYSTEM])
…

bin_PROGRAMS = hello
if LINUX
hello_SOURCES = hello-linux.c hello-common.c
else
hello_SOURCES = hello-generic.c hello-common.c
endif

bin_PROGRAMS = hello
hello_SOURCES = hello-common.c
if LINUX
hello_SOURCES += hello-linux.c
else
hello_SOURCES += hello-generic.c
endif

bin_PROGRAMS = cpio pax $(MT)
libexec_PROGRAMS = $(RMT)
EXTRA_PROGRAMS = mt rmt

bin_PROGRAMS = cpio pax
if WANT_MT
  bin_PROGRAMS += mt
endif
if WANT_RMT
  libexec_PROGRAMS = rmt
endif

7.2 Building a library

Building a library is much like building a program. In this case, the name of the primary is ‘LIBRARIES’. Libraries can be installed in libdir or pkglibdir.

See Building a Shared Library, for information on how to build shared libraries using libtool and the ‘LTLIBRARIES’ primary.

Each ‘_LIBRARIES’ variable is a list of the libraries to be built. For instance to create a library named libcpio.a, but not install it, you would write:

noinst_LIBRARIES = libcpio.a

The sources that go into a library are determined exactly as they are for programs, via the ‘_SOURCES’ variables. Note that the library name is canonicalized (see How derived variables are named), so the ‘_SOURCES’ variable corresponding to liblob.a is ‘liblob_a_SOURCES’, not ‘liblob.a_SOURCES’.

Extra objects can be added to a library using the ‘library_LIBADD’ variable. This should be used for objects determined by configure. Again from cpio:

libcpio_a_LIBADD = $(LIBOBJS) $(ALLOCA)

In addition, sources for extra objects that will not exist until configure-time must be added to the BUILT_SOURCES variable (see Built sources).

Building a static library is done by compiling all object files, then by invoking $(AR) $(ARFLAGS) followed by the name of the library and the list of objects, and finally by calling $(RANLIB) on that library. You should call AC_PROG_RANLIB from your configure.ac to define RANLIB (Automake will complain otherwise). AR and ARFLAGS default to ar and cru respectively; you can override these two variables my setting them in your Makefile.am, by AC_SUBSTing them from your configure.ac, or by defining a per-library maude_AR variable (see Program and Library Variables).

7.3 Building a Shared Library

Building shared libraries portably is a relatively complex matter. For this reason, GNU Libtool (see Introduction in The Libtool Manual) was created to help build shared libraries in a platform-independent way.

• The Libtool Concept
• Building Libtool Libraries
• Building Libtool Libraries Conditionally
• Libtool Libraries with Conditional Sources
• Libtool Convenience Libraries
• Libtool Modules
• _LIBADD and _LDFLAGS
• LTLIBOBJS
• Common Issues Related to Libtool’s Use

lib_LTLIBRARIES = libgettext.la
libgettext_la_SOURCES = gettext.c gettext.h …

EXTRA_LTLIBRARIES = libfoo.la libbar.la
lib_LTLIBRARIES = $(WANTEDLIBS)
libfoo_la_SOURCES = foo.c …
libfoo_la_LDFLAGS = -rpath '$(libdir)'
libbar_la_SOURCES = bar.c …
libbar_la_LDFLAGS = -rpath '$(libdir)'

lib_LTLIBRARIES =
if WANT_LIBFOO
lib_LTLIBRARIES += libfoo.la
endif
if WANT_LIBBAR
lib_LTLIBRARIES += libbar.la
endif
libfoo_la_SOURCES = foo.c …
libbar_la_SOURCES = bar.c …

lib_LTLIBRARIES = libhello.la
libhello_la_SOURCES = hello-common.c
EXTRA_libhello_la_SOURCES = hello-linux.c hello-generic.c
libhello_la_LIBADD = $(HELLO_SYSTEM)
libhello_la_DEPENDENCIES = $(HELLO_SYSTEM)

lib_LTLIBRARIES = libhello.la
libhello_la_SOURCES = hello-common.c
if LINUX
libhello_la_SOURCES += hello-linux.c
else
libhello_la_SOURCES += hello-generic.c
endif

# -- Top-level Makefile.am --
SUBDIRS = sub1 sub2 …
lib_LTLIBRARIES = libtop.la
libtop_la_SOURCES =
libtop_la_LIBADD = \
  sub1/libsub1.la \
  sub2/libsub2.la \
  …

# -- sub1/Makefile.am --
noinst_LTLIBRARIES = libsub1.la
libsub1_la_SOURCES = …

# -- sub2/Makefile.am --
# showing nested convenience libraries
SUBDIRS = sub2.1 sub2.2 …
noinst_LTLIBRARIES = libsub2.la
libsub2_la_SOURCES =
libsub2_la_LIBADD = \
  sub21/libsub21.la \
  sub22/libsub22.la \
  …

pkglib_LTLIBRARIES = mymodule.la
mymodule_la_SOURCES = doit.c
mymodule_la_LDFLAGS = -module

bin_PROGRAMS = prog
prog_SOURCES = prog.c foo.c …

lib_LTLIBRARIES = libfoo.la
libfoo_la_SOURCES = foo.c …

object `foo.$(OBJEXT)' created both with libtool and without

bin_PROGRAMS = prog
prog_SOURCES = prog.c foo.c …
prog_CFLAGS = $(AM_CFLAGS)

lib_LTLIBRARIES = libfoo.la
libfoo_la_SOURCES = foo.c …

7.4 Program and Library Variables

Associated with each program are a collection of variables which can be used to modify how that program is built. There is a similar list of such variables for each library. The canonical name of the program (or library) is used as a base for naming these variables.

In the list below, we use the name “maude” to refer to the program or library. In your Makefile.am you would replace this with the canonical name of your program. This list also refers to “maude” as a program, but in general the same rules apply for both static and dynamic libraries; the documentation below notes situations where programs and libraries differ.

‘maude_SOURCES’

This variable, if it exists, lists all the source files which are compiled to build the program. These files are added to the distribution by default. When building the program, Automake will cause each source file to be compiled to a single .o file (or .lo when using libtool). Normally these object files are named after the source file, but other factors can change this. If a file in the ‘_SOURCES’ variable has an unrecognized extension, Automake will do one of two things with it. If a suffix rule exists for turning files with the unrecognized extension into .o files, then automake will treat this file as it will any other source file (see Support for Other Languages). Otherwise, the file will be ignored as though it were a header file.

The prefixes ‘dist_’ and ‘nodist_’ can be used to control whether files listed in a ‘_SOURCES’ variable are distributed. ‘dist_’ is redundant, as sources are distributed by default, but it can be specified for clarity if desired.

It is possible to have both ‘dist_’ and ‘nodist_’ variants of a given ‘_SOURCES’ variable at once; this lets you easily distribute some files and not others, for instance:

nodist_maude_SOURCES = nodist.c
dist_maude_SOURCES = dist-me.c

By default the output file (on Unix systems, the .o file) will be put into the current build directory. However, if the option subdir-objects is in effect in the current directory then the .o file will be put into the subdirectory named after the source file. For instance, with subdir-objects enabled, sub/dir/file.c will be compiled to sub/dir/file.o. Some people prefer this mode of operation. You can specify subdir-objects in AUTOMAKE_OPTIONS (see Changing Automake’s Behavior).

‘EXTRA_maude_SOURCES’

Automake needs to know the list of files you intend to compile statically. For one thing, this is the only way Automake has of knowing what sort of language support a given Makefile.in requires. ⁴ This means that, for example, you can’t put a configure substitution like ‘@my_sources@’ into a ‘_SOURCES’ variable. If you intend to conditionally compile source files and use configure to substitute the appropriate object names into, e.g., ‘_LDADD’ (see below), then you should list the corresponding source files in the ‘EXTRA_’ variable.

This variable also supports ‘dist_’ and ‘nodist_’ prefixes, e.g., ‘nodist_EXTRA_maude_SOURCES’.

‘maude_AR’

A static library is created by default by invoking $(AR) $(ARFLAGS) followed by the name of the library and then the objects being put into the library. You can override this by setting the ‘_AR’ variable. This is usually used with C++; some C++ compilers require a special invocation in order to instantiate all the templates which should go into a library. For instance, the SGI C++ compiler likes this variable set like so:

libmaude_a_AR = $(CXX) -ar -o

‘maude_LIBADD’

Extra objects can be added to a library using the ‘_LIBADD’ variable. For instance this should be used for objects determined by configure (see Building a library).

‘maude_LDADD’

Extra objects can be added to a program by listing them in the ‘_LDADD’ variable. For instance this should be used for objects determined by configure (see Linking the program).

‘_LDADD’ and ‘_LIBADD’ are inappropriate for passing program-specific linker flags (except for ‘-l’, ‘-L’, ‘-dlopen’ and ‘-dlpreopen’). Use the ‘_LDFLAGS’ variable for this purpose.

For instance, if your configure.ac uses AC_PATH_XTRA, you could link your program against the X libraries like so:

maude_LDADD = $(X_PRE_LIBS) $(X_LIBS) $(X_EXTRA_LIBS)

‘maude_LDFLAGS’

This variable is used to pass extra flags to the link step of a program or a shared library.

‘maude_DEPENDENCIES’

It is also occasionally useful to have a program depend on some other target which is not actually part of that program. This can be done using the ‘_DEPENDENCIES’ variable. Each program depends on the contents of such a variable, but no further interpretation is done.

If ‘_DEPENDENCIES’ is not supplied, it is computed by Automake. The automatically-assigned value is the contents of ‘_LDADD’ or ‘_LIBADD’, with most configure substitutions, ‘-l’, ‘-L’, ‘-dlopen’ and ‘-dlpreopen’ options removed. The configure substitutions that are left in are only ‘$(LIBOBJS)’ and ‘$(ALLOCA)’; these are left because it is known that they will not cause an invalid value for ‘_DEPENDENCIES’ to be generated.

‘maude_LINK’

You can override the linker on a per-program basis. By default the linker is chosen according to the languages used by the program. For instance, a program that includes C++ source code would use the C++ compiler to link. The ‘_LINK’ variable must hold the name of a command which can be passed all the .o file names as arguments. Note that the name of the underlying program is not passed to ‘_LINK’; typically one uses ‘$@’:

maude_LINK = $(CCLD) -magic -o $@

‘maude_CCASFLAGS’ ¶

‘maude_CFLAGS’

‘maude_CPPFLAGS’

‘maude_CXXFLAGS’

‘maude_FFLAGS’

‘maude_GCJFLAGS’

‘maude_LFLAGS’

‘maude_OBJCFLAGS’

‘maude_RFLAGS’

‘maude_YFLAGS’

Automake allows you to set compilation flags on a per-program (or per-library) basis. A single source file can be included in several programs, and it will potentially be compiled with different flags for each program. This works for any language directly supported by Automake. These per-target compilation flags are ‘_CCASFLAGS’, ‘_CFLAGS’, ‘_CPPFLAGS’, ‘_CXXFLAGS’, ‘_FFLAGS’, ‘_GCJFLAGS’, ‘_LFLAGS’, ‘_OBJCFLAGS’, ‘_RFLAGS’, and ‘_YFLAGS’.

When using a per-target compilation flag, Automake will choose a different name for the intermediate object files. Ordinarily a file like sample.c will be compiled to produce sample.o. However, if the program’s ‘_CFLAGS’ variable is set, then the object file will be named, for instance, maude-sample.o. (See also Why are object files sometimes renamed?.)

In compilations with per-target flags, the ordinary ‘AM_’ form of the flags variable is not automatically included in the compilation (however, the user form of the variable is included). So for instance, if you want the hypothetical maude compilations to also use the value of ‘AM_CFLAGS’, you would need to write:

maude_CFLAGS = … your flags … $(AM_CFLAGS)

‘maude_SHORTNAME’

On some platforms the allowable file names are very short. In order to support these systems and per-target compilation flags at the same time, Automake allows you to set a “short name” which will influence how intermediate object files are named. For instance, in the following example,

bin_PROGRAMS = maude
maude_CPPFLAGS = -DSOMEFLAG
maude_SHORTNAME = m
maude_SOURCES = sample.c …

the object file would be named m-sample.o rather than maude-sample.o.

This facility is rarely needed in practice, and we recommend avoiding it until you find it is required.

7.5 Default _SOURCES

_SOURCES variables are used to specify source files of programs (see Building a program), libraries (see Building a library), and Libtool libraries (see Building a Shared Library).

When no such variable is specified for a target, Automake will define one itself. The default is to compile a single C file whose base name is the name of the target itself, with any extension replaced by .c. (Defaulting to C is terrible but we are stuck with it for historical reasons.)

For example if you have the following somewhere in your Makefile.am with no corresponding ‘libfoo_a_SOURCES’:

lib_LIBRARIES = libfoo.a sub/libc++.a

libfoo.a will be built using a default source file named libfoo.c, and sub/libc++.a will be built from sub/libc++.c. (In older versions sub/libc++.a would be built from sub_libc___a.c, i.e., the default source was the canonized name of the target, with .c appended. We believe the new behavior is more sensible, but for backward compatibility automake will use the old name if a file or a rule with that name exist.)

Default sources are mainly useful in test suites, when building many tests programs each from a single source. For instance in

check_PROGRAMS = test1 test2 test3

test1, test2, and test3 will be built from test1.c, test2.c, and test3.c.

Another case where is this convenient is building many Libtool modules (moduleN.la), each defined in its own file (moduleN.c).

AM_LDFLAGS = -module
lib_LTLIBRARIES = module1.la module2.la module3.la

Finally, there is one situation where this default source computation needs to be avoided: when a target should not be built from sources. We already saw such an example in Building true and false; this happens when all the constituents of a target have already been compiled and need just to be combined using a _LDADD variable. Then it is necessary to define an empty _SOURCES variable, so that automake does not compute a default.

bin_PROGRAMS = target
target_SOURCES =
target_LDADD = libmain.a libmisc.a

7.6 Special handling for LIBOBJS and ALLOCA

Automake explicitly recognizes the use of $(LIBOBJS) and $(ALLOCA), and uses this information, plus the list of LIBOBJS files derived from configure.ac to automatically include the appropriate source files in the distribution (see What Goes in a Distribution). These source files are also automatically handled in the dependency-tracking scheme; see See Automatic dependency tracking.

$(LIBOBJS) and $(ALLOCA) are specially recognized in any ‘_LDADD’ or ‘_LIBADD’ variable.

7.7 Variables used when building a program

Occasionally it is useful to know which Makefile variables Automake uses for compilations; for instance you might need to do your own compilation in some special cases.

Some variables are inherited from Autoconf; these are CC, CFLAGS, CPPFLAGS, DEFS, LDFLAGS, and LIBS.

There are some additional variables which Automake itself defines:

AM_CPPFLAGS ¶

The contents of this variable are passed to every compilation which invokes the C preprocessor; it is a list of arguments to the preprocessor. For instance, ‘-I’ and ‘-D’ options should be listed here.

Automake already provides some ‘-I’ options automatically. In particular it generates ‘-I$(srcdir)’, ‘-I.’, and a ‘-I’ pointing to the directory holding config.h (if you’ve used AC_CONFIG_HEADERS or AM_CONFIG_HEADER). You can disable the default ‘-I’ options using the ‘nostdinc’ option.

AM_CPPFLAGS is ignored in preference to a per-executable (or per-library) _CPPFLAGS variable if it is defined.

INCLUDES ¶

This does the same job as ‘AM_CPPFLAGS’ (or any per-target ‘_CPPFLAGS’ variable if it is used). It is an older name for the same functionality. This variable is deprecated; we suggest using ‘AM_CPPFLAGS’ and per-target ‘_CPPFLAGS’ instead.

AM_CFLAGS ¶

This is the variable which the Makefile.am author can use to pass in additional C compiler flags. It is more fully documented elsewhere. In some situations, this is not used, in preference to the per-executable (or per-library) _CFLAGS.

COMPILE ¶

This is the command used to actually compile a C source file. The filename is appended to form the complete command line.

AM_LDFLAGS ¶

This is the variable which the Makefile.am author can use to pass in additional linker flags. In some situations, this is not used, in preference to the per-executable (or per-library) _LDFLAGS.

LINK ¶

This is the command used to actually link a C program. It already includes ‘-o $@’ and the usual variable references (for instance, CFLAGS); it takes as “arguments” the names of the object files and libraries to link in.

7.8 Yacc and Lex support

Automake has somewhat idiosyncratic support for Yacc and Lex.

Automake assumes that the .c file generated by yacc (or lex) should be named using the basename of the input file. That is, for a yacc source file foo.y, Automake will cause the intermediate file to be named foo.c (as opposed to y.tab.c, which is more traditional).

The extension of a yacc source file is used to determine the extension of the resulting ‘C’ or ‘C++’ file. Files with the extension ‘.y’ will be turned into ‘.c’ files; likewise, ‘.yy’ will become ‘.cc’; ‘.y++’, ‘c++’; and ‘.yxx’, ‘.cxx’.

Likewise, lex source files can be used to generate ‘C’ or ‘C++’; the extensions ‘.l’, ‘.ll’, ‘.l++’, and ‘.lxx’ are recognized.

You should never explicitly mention the intermediate (‘C’ or ‘C++’) file in any ‘SOURCES’ variable; only list the source file.

The intermediate files generated by yacc (or lex) will be included in any distribution that is made. That way the user doesn’t need to have yacc or lex.

If a yacc source file is seen, then your configure.ac must define the variable ‘YACC’. This is most easily done by invoking the macro ‘AC_PROG_YACC’ (see Particular Program Checks in The Autoconf Manual).

When yacc is invoked, it is passed ‘YFLAGS’ and ‘AM_YFLAGS’. The former is a user variable and the latter is intended for the Makefile.am author.

‘AM_YFLAGS’ is usually used to pass the -d option to yacc. Automake knows what this means and will automatically adjust its rules to update and distribute the header file built by yacc -d. What Automake cannot guess, though, is where this header will be used: it is up to you to ensure the header gets built before it is first used. Typically this is necessary in order for dependency tracking to work when the header is included by another file. The common solution is listing the header file in BUILT_SOURCES (see Built sources) as follows.

BUILT_SOURCES = parser.h
AM_YFLAGS = -d
bin_PROGRAMS = foo
foo_SOURCES = … parser.y …

If a lex source file is seen, then your configure.ac must define the variable ‘LEX’. You can use ‘AC_PROG_LEX’ to do this (see Particular Program Checks in The Autoconf Manual), but using AM_PROG_LEX macro (see Autoconf macros supplied with Automake) is recommended.

When lex is invoked, it is passed ‘LFLAGS’ and ‘AM_LFLAGS’. The former is a user variable and the latter is intended for the Makefile.am author.

Automake makes it possible to include multiple yacc (or lex) source files in a single program. When there is more than one distinct yacc (or lex) source file in a directory, Automake uses a small program called ylwrap to run yacc (or lex) in a subdirectory. This is necessary because yacc’s output filename is fixed, and a parallel make could conceivably invoke more than one instance of yacc simultaneously. The ylwrap program is distributed with Automake. It should appear in the directory specified by ‘AC_CONFIG_AUX_DIR’, or one of its default locations (see Finding ‘configure’ Input in The Autoconf Manual).

For yacc, simply managing locking is insufficient. The output of yacc always uses the same symbol names internally, so it isn’t possible to link two yacc parsers into the same executable.

We recommend using the following renaming hack used in gdb:

#define	yymaxdepth c_maxdepth
#define	yyparse	c_parse
#define	yylex	c_lex
#define	yyerror	c_error
#define	yylval	c_lval
#define	yychar	c_char
#define	yydebug	c_debug
#define	yypact	c_pact
#define	yyr1	c_r1
#define	yyr2	c_r2
#define	yydef	c_def
#define	yychk	c_chk
#define	yypgo	c_pgo
#define	yyact	c_act
#define	yyexca	c_exca
#define yyerrflag c_errflag
#define yynerrs	c_nerrs
#define	yyps	c_ps
#define	yypv	c_pv
#define	yys	c_s
#define	yy_yys	c_yys
#define	yystate	c_state
#define	yytmp	c_tmp
#define	yyv	c_v
#define	yy_yyv	c_yyv
#define	yyval	c_val
#define	yylloc	c_lloc
#define yyreds	c_reds
#define yytoks	c_toks
#define yylhs	c_yylhs
#define yylen	c_yylen
#define yydefred c_yydefred
#define yydgoto	c_yydgoto
#define yysindex c_yysindex
#define yyrindex c_yyrindex
#define yygindex c_yygindex
#define yytable	 c_yytable
#define yycheck	 c_yycheck
#define yyname   c_yyname
#define yyrule   c_yyrule

For each define, replace the ‘c_’ prefix with whatever you like. These defines work for bison, byacc, and traditional yaccs. If you find a parser generator that uses a symbol not covered here, please report the new name so it can be added to the list.

7.9 C++ Support

Automake includes full support for C++.

Any package including C++ code must define the output variable ‘CXX’ in configure.ac; the simplest way to do this is to use the AC_PROG_CXX macro (see Particular Program Checks in The Autoconf Manual).

A few additional variables are defined when a C++ source file is seen:

CXX ¶

The name of the C++ compiler.

CXXFLAGS ¶

Any flags to pass to the C++ compiler.

AM_CXXFLAGS ¶

The maintainer’s variant of CXXFLAGS.

CXXCOMPILE ¶

The command used to actually compile a C++ source file. The file name is appended to form the complete command line.

CXXLINK ¶

The command used to actually link a C++ program.

7.10 Assembly Support

Automake includes some support for assembly code.

The variable CCAS holds the name of the compiler used to build assembly code. This compiler must work a bit like a C compiler; in particular it must accept ‘-c’ and ‘-o’. The value of CCASFLAGS is passed to the compilation.

You are required to set CCAS and CCASFLAGS via configure.ac. The autoconf macro AM_PROG_AS will do this for you. Unless they are already set, it simply sets CCAS to the C compiler and CCASFLAGS to the C compiler flags.

Only the suffixes ‘.s’ and ‘.S’ are recognized by automake as being files containing assembly code.

7.11 Fortran 77 Support

Automake includes full support for Fortran 77.

Any package including Fortran 77 code must define the output variable ‘F77’ in configure.ac; the simplest way to do this is to use the AC_PROG_F77 macro (see Particular Program Checks in The Autoconf Manual).

A few additional variables are defined when a Fortran 77 source file is seen:

F77 ¶

The name of the Fortran 77 compiler.

FFLAGS ¶

Any flags to pass to the Fortran 77 compiler.

AM_FFLAGS ¶

The maintainer’s variant of FFLAGS.

RFLAGS ¶

Any flags to pass to the Ratfor compiler.

AM_RFLAGS ¶

The maintainer’s variant of RFLAGS.

F77COMPILE ¶

The command used to actually compile a Fortran 77 source file. The file name is appended to form the complete command line.

FLINK ¶

The command used to actually link a pure Fortran 77 program or shared library.

Automake can handle preprocessing Fortran 77 and Ratfor source files in addition to compiling them⁵. Automake also contains some support for creating programs and shared libraries that are a mixture of Fortran 77 and other languages (see Mixing Fortran 77 With C and C++).

These issues are covered in the following sections.

• Preprocessing Fortran 77
• Compiling Fortran 77 Files
• Mixing Fortran 77 With C and C++

bin_PROGRAMS = foo
foo_SOURCES  = main.cc foo.f
foo_LDADD    = libfoo.la $(FLIBS)

pkglib_LTLIBRARIES = libfoo.la
libfoo_la_SOURCES  = bar.f baz.c zardoz.cc
libfoo_la_LIBADD   = $(FLIBS)

                     \              Linker
          source      \
           code        \     C        C++     Fortran
     -----------------  +---------+---------+---------+
                        |         |         |         |
     C                  |    x    |         |         |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
         C++            |         |    x    |         |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
               Fortran  |         |         |    x    |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
     C + C++            |         |    x    |         |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
     C +       Fortran  |         |         |    x    |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
         C++ + Fortran  |         |    x    |         |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
     C + C++ + Fortran  |         |    x    |         |
                        |         |         |         |
                        +---------+---------+---------+

7.12 Fortran 9x Support

Automake includes full support for Fortran 9x.

Any package including Fortran 9x code must define the output variable ‘FC’ in configure.ac; the simplest way to do this is to use the AC_PROG_FC macro (see Particular Program Checks in The Autoconf Manual).

A few additional variables are defined when a Fortran 9x source file is seen:

FC ¶

The name of the Fortran 9x compiler.

FCFLAGS ¶

Any flags to pass to the Fortran 9x compiler.

AM_FCFLAGS ¶

The maintainer’s variant of FCFLAGS.

FCCOMPILE ¶

The command used to actually compile a Fortran 9x source file. The file name is appended to form the complete command line.

FCLINK ¶

The command used to actually link a pure Fortran 9x program or shared library.

• Compiling Fortran 9x Files

7.13 Java Support

Automake includes support for compiled Java, using gcj, the Java front end to the GNU Compiler Collection.

Any package including Java code to be compiled must define the output variable ‘GCJ’ in configure.ac; the variable ‘GCJFLAGS’ must also be defined somehow (either in configure.ac or Makefile.am). The simplest way to do this is to use the AM_PROG_GCJ macro.

By default, programs including Java source files are linked with gcj.

As always, the contents of ‘AM_GCJFLAGS’ are passed to every compilation invoking gcj (in its role as an ahead-of-time compiler – when invoking it to create .class files, ‘AM_JAVACFLAGS’ is used instead). If it is necessary to pass options to gcj from Makefile.am, this variable, and not the user variable ‘GCJFLAGS’, should be used.

gcj can be used to compile .java, .class, .zip, or .jar files.

When linking, gcj requires that the main class be specified using the ‘--main=’ option. The easiest way to do this is to use the _LDFLAGS variable for the program.

7.14 Support for Other Languages

Automake currently only includes full support for C, C++ (see C++ Support), Fortran 77 (see Fortran 77 Support), Fortran 9x (see Fortran 9x Support), and Java (see Java Support). There is only rudimentary support for other languages, support for which will be improved based on user demand.

Some limited support for adding your own languages is available via the suffix rule handling; see Handling new file extensions.

7.15 Automatic de-ANSI-fication

Although the GNU standards allow the use of ANSI C, this can have the effect of limiting portability of a package to some older compilers (notably the SunOS C compiler).

Automake allows you to work around this problem on such machines by de-ANSI-fying each source file before the actual compilation takes place.

If the Makefile.am variable AUTOMAKE_OPTIONS (see Changing Automake’s Behavior) contains the option ansi2knr then code to handle de-ANSI-fication is inserted into the generated Makefile.in.

This causes each C source file in the directory to be treated as ANSI C. If an ANSI C compiler is available, it is used. If no ANSI C compiler is available, the ansi2knr program is used to convert the source files into K&R C, which is then compiled.

The ansi2knr program is simple-minded. It assumes the source code will be formatted in a particular way; see the ansi2knr man page for details.

Support for de-ANSI-fication requires the source files ansi2knr.c and ansi2knr.1 to be in the same package as the ANSI C source; these files are distributed with Automake. Also, the package configure.ac must call the macro AM_C_PROTOTYPES (see Autoconf macros supplied with Automake).

Automake also handles finding the ansi2knr support files in some other directory in the current package. This is done by prepending the relative path to the appropriate directory to the ansi2knr option. For instance, suppose the package has ANSI C code in the src and lib subdirectories. The files ansi2knr.c and ansi2knr.1 appear in lib. Then this could appear in src/Makefile.am:

AUTOMAKE_OPTIONS = ../lib/ansi2knr

If no directory prefix is given, the files are assumed to be in the current directory.

Note that automatic de-ANSI-fication will not work when the package is being built for a different host architecture. That is because automake currently has no way to build ansi2knr for the build machine.

Using LIBOBJS with source de-ANSI-fication used to require hand-crafted code in configure to append $U to basenames in LIBOBJS. This is no longer true today. Starting with version 2.54, Autoconf takes care of rewriting LIBOBJS and LTLIBOBJS. (see AC_LIBOBJ vs. LIBOBJS in The Autoconf Manual)

7.16 Automatic dependency tracking

As a developer it is often painful to continually update the Makefile.in whenever the include-file dependencies change in a project. Automake supplies a way to automatically track dependency changes.

Automake always uses complete dependencies for a compilation, including system headers. Automake’s model is that dependency computation should be a side effect of the build. To this end, dependencies are computed by running all compilations through a special wrapper program called depcomp. depcomp understands how to coax many different C and C++ compilers into generating dependency information in the format it requires. automake -a will install depcomp into your source tree for you. If depcomp can’t figure out how to properly invoke your compiler, dependency tracking will simply be disabled for your build.

Experience with earlier versions of Automake ⁷ taught us that it is not reliable to generate dependencies only on the maintainer’s system, as configurations vary too much. So instead Automake implements dependency tracking at build time.

Automatic dependency tracking can be suppressed by putting no-dependencies in the variable AUTOMAKE_OPTIONS, or passing no-dependencies as an argument to AM_INIT_AUTOMAKE (this should be the preferred way). Or, you can invoke automake with the -i option. Dependency tracking is enabled by default.

The person building your package also can choose to disable dependency tracking by configuring with --disable-dependency-tracking.

7.17 Support for executable extensions

On some platforms, such as Windows, executables are expected to have an extension such as ‘.exe’. On these platforms, some compilers (GCC among them) will automatically generate foo.exe when asked to generate foo.

Automake provides mostly-transparent support for this. Unfortunately mostly doesn’t yet mean fully. Until the English dictionary is revised, you will have to assist Automake if your package must support those platforms.

One thing you must be aware of is that, internally, Automake rewrites something like this:

bin_PROGRAMS = liver

to this:

bin_PROGRAMS = liver$(EXEEXT)

The targets Automake generates are likewise given the ‘$(EXEEXT)’ extension. EXEEXT

However, Automake cannot apply this rewriting to configure substitutions. This means that if you are conditionally building a program using such a substitution, then your configure.ac must take care to add ‘$(EXEEXT)’ when constructing the output variable.

With Autoconf 2.13 and earlier, you must explicitly use AC_EXEEXT to get this support. With Autoconf 2.50, AC_EXEEXT is run automatically if you configure a compiler (say, through AC_PROG_CC).

Sometimes maintainers like to write an explicit link rule for their program. Without executable extension support, this is easy—you simply write a rule whose target is the name of the program. However, when executable extension support is enabled, you must instead add the ‘$(EXEEXT)’ suffix.

Unfortunately, due to the change in Autoconf 2.50, this means you must always add this extension. However, this is a problem for maintainers who know their package will never run on a platform that has executable extensions. For those maintainers, the no-exeext option (see Changing Automake’s Behavior) will disable this feature. This works in a fairly ugly way; if no-exeext is seen, then the presence of a rule for a target named foo in Makefile.am will override an automake-generated rule for foo$(EXEEXT). Without the no-exeext option, this use will give a diagnostic.

8.1 Executable Scripts

It is possible to define and install programs which are scripts. Such programs are listed using the ‘SCRIPTS’ primary name. Automake doesn’t define any dependencies for scripts; the Makefile.am should include the appropriate rules.

Automake does not assume that scripts are derived objects; such objects must be deleted by hand (see What Gets Cleaned).

The automake program itself is a Perl script that is generated from automake.in. Here is how this is handled:

bin_SCRIPTS = automake
CLEANFILES = $(bin_SCRIPTS)

do_subst = sed -e 's,[@]datadir[@],$(datadir),g' \
            -e 's,[@]PERL[@],$(PERL),g' \
            -e 's,[@]PACKAGE[@],$(PACKAGE),g' \
            -e 's,[@]VERSION[@],$(VERSION),g' \
            …

automake: automake.in Makefile
        $(do_subst) < $(srcdir)/automake.in > automake
        chmod +x automake

Because—as we have just seen—scripts can be built, they are not distributed by default. Scripts that should be distributed can be specified using a dist_ prefix as in other primaries. For instance the following Makefile.am declares that my_script should be distributed and installed in $(sbindir).

dist_sbin_SCRIPTS = my_script

Script objects can be installed in bindir, sbindir, libexecdir, or pkgdatadir.

Scripts that need not being installed can be listed in noinst_SCRIPTS, and among them, those which are needed only by make check should go in check_SCRIPTS.

8.2 Header files

Header files that must be installed are specified by the ‘HEADERS’ family of variables. Headers can be installed in includedir, oldincludedir, pkgincludedir or any other directory you may have defined (see The Uniform Naming Scheme). For instance

include_HEADERS = foo.h bar/bar.h

will install the two files as $(includedir)/foo.h and $(includedir)/bar.h.

The ‘nobase_’ prefix is also supported,

nobase_include_HEADERS = foo.h bar/bar.h

will install the two files as $(includedir)/foo.h and $(includedir)/bar/bar.h (see An Alternative Approach to Subdirectories).

Usually, only header files that accompany installed libraries need to be installed. Headers used by programs or convenience libraries are not installed. The noinst_HEADERS variable can be used for such headers. However when the header actually belongs to one convenient library or program, we recommend listing it in the program’s or library’s ‘_SOURCES’ variable (see Defining program sources) instead of in noinst_HEADERS. This is clearer for the Makefile.am reader. noinst_HEADERS would be the right variable to use in a directory containing only headers and no associated library or program.

All header files must be listed somewhere; in a ‘_SOURCES’ variable or in a ‘_HEADERS’ variable. Missing ones will not appear in the distribution.

For header files that are built and must not be distributed, use the ‘nodist_’ prefix as in nodist_include_HEADERS or nodist_prog_SOURCES. If these generated headers are needed during the build, you must also ensure they exist before they are used, see See Built sources.

8.3 Architecture-independent data files

Automake supports the installation of miscellaneous data files using the ‘DATA’ family of variables.

Such data can be installed in the directories datadir, sysconfdir, sharedstatedir, localstatedir, or pkgdatadir.

By default, data files are not included in a distribution. Of course, you can use the ‘dist_’ prefix to change this on a per-variable basis.

Here is how Automake declares its auxiliary data files:

dist_pkgdata_DATA = clean-kr.am clean.am …

8.4 Built sources

Because Automake’s automatic dependency tracking works as a side-effect of compilation (see Automatic dependency tracking) there is a bootstrap issue: a target should not be compiled before its dependencies are made, but these dependencies are unknown until the target is first compiled.

Ordinarily this is not a problem, because dependencies are distributed sources: they preexist and do not need to be built. Suppose that foo.c includes foo.h. When it first compiles foo.o, make only knows that foo.o depends on foo.c. As a side-effect of this compilation depcomp records the foo.h dependency so that following invocations of make will honor it. In these conditions, it’s clear there is no problem: either foo.o doesn’t exist and has to be built (regardless of the dependencies), either accurate dependencies exist and they can be used to decide whether foo.o should be rebuilt.

It’s a different story if foo.h doesn’t exist by the first make run. For instance there might be a rule to build foo.h. This time file.o’s build will fail because the compiler can’t find foo.h. make failed to trigger the rule to build foo.h first by lack of dependency information.

The BUILT_SOURCES variable is a workaround for this problem. A source file listed in BUILT_SOURCES is made on make all or make check (or even make install) before other targets are processed. However, such a source file is not compiled unless explicitly requested by mentioning it in some other ‘_SOURCES’ variable.

So, to conclude our introductory example, we could use BUILT_SOURCES = foo.h to ensure foo.h gets built before any other target (including foo.o) during make all or make check.

BUILT_SOURCES is actually a bit of a misnomer, as any file which must be created early in the build process can be listed in this variable. Moreover, all built sources do not necessarily have to be listed in BUILT_SOURCES. For instance a generated .c file doesn’t need to appear in BUILT_SOURCES (unless it is included by another source), because it’s a known dependency of the associated object.

It might be important to emphasize that BUILT_SOURCES is honored only by make all, make check and make install. This means you cannot build a specific target (e.g., make foo) in a clean tree if it depends on a built source. However it will succeed if you have run make all earlier, because accurate dependencies are already available.

The next section illustrates and discusses the handling of built sources on a toy example.

• Built sources example
• First try
• Using BUILT_SOURCES
• Recording dependencies manually
• Build bindir.h from configure
• Build bindir.c, not bindir.h.
• Which is best?

# This won't work.
bin_PROGRAMS = foo
foo_SOURCES = foo.c
nodist_foo_SOURCES = bindir.h
CLEANFILES = bindir.h
bindir.h: Makefile
        echo '#define bindir "$(bindir)"' >$@

% make
source='foo.c' object='foo.o' libtool=no \
depfile='.deps/foo.Po' tmpdepfile='.deps/foo.TPo' \
depmode=gcc /bin/sh ./depcomp \
gcc -I. -I. -g -O2 -c `test -f 'foo.c' || echo './'`foo.c
foo.c:2: bindir.h: No such file or directory
make: *** [foo.o] Error 1

bin_PROGRAMS = foo
foo_SOURCES = foo.c
nodist_foo_SOURCES = bindir.h
BUILT_SOURCES = bindir.h
CLEANFILES = bindir.h
bindir.h: Makefile
        echo '#define bindir "$(bindir)"' >$@

% make
echo '#define bindir "/usr/local/bin"' >bindir.h
make  all-am
make[1]: Entering directory `/home/adl/tmp'
source='foo.c' object='foo.o' libtool=no \
depfile='.deps/foo.Po' tmpdepfile='.deps/foo.TPo' \
depmode=gcc /bin/sh ./depcomp \
gcc -I. -I. -g -O2 -c `test -f 'foo.c' || echo './'`foo.c
gcc  -g -O2   -o foo  foo.o
make[1]: Leaving directory `/home/adl/tmp'

% make clean
test -z "bindir.h" || rm -f bindir.h
test -z "foo" || rm -f foo
rm -f *.o
% : > .deps/foo.Po # Suppress previously recorded dependencies
% make foo
source='foo.c' object='foo.o' libtool=no \
depfile='.deps/foo.Po' tmpdepfile='.deps/foo.TPo' \
depmode=gcc /bin/sh ./depcomp \
gcc -I. -I. -g -O2 -c `test -f 'foo.c' || echo './'`foo.c
foo.c:2: bindir.h: No such file or directory
make: *** [foo.o] Error 1

bin_PROGRAMS = foo
foo_SOURCES = foo.c
nodist_foo_SOURCES = bindir.h
foo.$(OBJEXT): bindir.h
CLEANFILES = bindir.h
bindir.h: Makefile
        echo '#define bindir "$(bindir)"' >$@

bin_PROGRAMS = foo
foo_SOURCES = foo.c

noinst_PROGRAMS = foo
foo_SOURCES = foo.c bindir.h
nodist_foo_SOURCES = bindir.c
CLEANFILES = bindir.c
bindir.c: Makefile
        echo 'const char bindir[] = "$(bindir)";' >$ 

9.1 Emacs Lisp

Automake provides some support for Emacs Lisp. The ‘LISP’ primary is used to hold a list of .el files. Possible prefixes for this primary are ‘lisp_’ and ‘noinst_’. Note that if lisp_LISP is defined, then configure.ac must run AM_PATH_LISPDIR (see Autoconf macros supplied with Automake).

Automake will byte-compile all Emacs Lisp source files using the Emacs found by AM_PATH_LISPDIR, if any was found.

Byte-compiled Emacs Lisp files are not portable among all versions of Emacs, so it makes sense to turn this off if you expect sites to have more than one version of Emacs installed. Furthermore, many packages don’t actually benefit from byte-compilation. Still, we recommend that you byte-compile your Emacs Lisp sources. It is probably better for sites with strange setups to cope for themselves than to make the installation less nice for everybody else.

There are two ways to avoid byte-compiling. Historically, we have recommended the following construct.

lisp_LISP = file1.el file2.el
ELCFILES =

ELCFILES is an internal Automake variable that normally lists all .elc files that must be byte-compiled. Automake defines ELCFILES automatically from lisp_LISP. Emptying this variable explicitly prevents byte-compilation to occur.

Since Automake 1.8, we now recommend using lisp_DATA instead. As in

lisp_DATA = file1.el file2.el

Note that these two constructs are not equivalent. _LISP will not install a file if Emacs is not installed, while _DATA will always install its files.

9.2 Gettext

If AM_GNU_GETTEXT is seen in configure.ac, then Automake turns on support for GNU gettext, a message catalog system for internationalization (see GNU Gettext in GNU gettext utilities).

The gettext support in Automake requires the addition of two subdirectories to the package, intl and po. Automake insures that these directories exist and are mentioned in SUBDIRS.

Lisp sources are not distributed by default. You can prefix the LISP primary with dist_, as in dist_lisp_LISP or dist_noinst_LISP, to indicate that these files should be distributed.

9.3 Libtool

Automake provides support for GNU Libtool (see Introduction in The Libtool Manual) with the ‘LTLIBRARIES’ primary. See Building a Shared Library.

9.4 Java

Automake provides some minimal support for Java compilation with the ‘JAVA’ primary.

Any .java files listed in a ‘_JAVA’ variable will be compiled with JAVAC at build time. By default, .class files are not included in the distribution.

Currently Automake enforces the restriction that only one ‘_JAVA’ primary can be used in a given Makefile.am. The reason for this restriction is that, in general, it isn’t possible to know which .class files were generated from which .java files – so it would be impossible to know which files to install where. For instance, a .java file can define multiple classes; the resulting .class file names cannot be predicted without parsing the .java file.

There are a few variables which are used when compiling Java sources:

JAVAC ¶

The name of the Java compiler. This defaults to ‘javac’.

JAVACFLAGS ¶

The flags to pass to the compiler. This is considered to be a user variable (see Variables reserved for the user).

AM_JAVACFLAGS ¶

More flags to pass to the Java compiler. This, and not JAVACFLAGS, should be used when it is necessary to put Java compiler flags into Makefile.am.

JAVAROOT ¶

The value of this variable is passed to the ‘-d’ option to javac. It defaults to ‘$(top_builddir)’.

CLASSPATH_ENV ¶

This variable is an sh expression which is used to set the CLASSPATH environment variable on the javac command line. (In the future we will probably handle class path setting differently.)

9.5 Python

Automake provides support for Python compilation with the ‘PYTHON’ primary.

Any files listed in a ‘_PYTHON’ variable will be byte-compiled with py-compile at install time. py-compile actually creates both standard (.pyc) and byte-compiled (.pyo) versions of the source files. Note that because byte-compilation occurs at install time, any files listed in ‘noinst_PYTHON’ will not be compiled. Python source files are included in the distribution by default.

Automake ships with an Autoconf macro called AM_PATH_PYTHON which will determine some Python-related directory variables (see below). If you have called AM_PATH_PYTHON from configure.ac, then you may use the following variables to list you Python source files in your variables: ‘python_PYTHON’, ‘pkgpython_PYTHON’, ‘pyexecdir_PYTHON’, ‘pkgpyexecdir_PYTHON’, depending where you want your files installed.

AM_PATH_PYTHON([VERSION], [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND]) takes three optional arguments. It will search a Python interpreter on the system. The first argument, if present, is the minimum version of Python required for this package: AM_PATH_PYTHON will skip any Python interpreter which is older than VERSION. If an interpreter is found and satisfies VERSION, then ACTION-IF-FOUND is run. Otherwise, ACTION-IF-NOT-FOUND is run.

If ACTION-IF-NOT-FOUND is not specified, the default is to abort configure. This is fine when Python is an absolute requirement for the package. Therefore if Python >= 2.2 is only optional to the package, AM_PATH_PYTHON could be called as follows.

  AM_PATH_PYTHON(2.2,, :)

AM_PATH_PYTHON creates several output variables based on the Python installation found during configuration.

PYTHON ¶

The name of the Python executable, or : if no suitable interpreter could be found.

Assuming ACTION-IF-NOT-FOUND is used (otherwise ./configure will abort if Python is absent), the value of PYTHON can be used to setup a conditional in order to disable the relevant part of a build as follows.

  AM_PATH_PYTHON(,, :)
  AM_CONDITIONAL([HAVE_PYTHON], [test "$PYTHON" != :])

If the ACTION-IF-NOT-FOUND is specified

PYTHON_VERSION ¶

The Python version number, in the form major.minor (e.g. ‘1.5’). This is currently the value of sys.version[:3].

PYTHON_PREFIX ¶

The string ${prefix}. This term may be used in future work which needs the contents of Python’s sys.prefix, but general consensus is to always use the value from configure.

PYTHON_EXEC_PREFIX ¶

The string ${exec_prefix}. This term may be used in future work which needs the contents of Python’s sys.exec_prefix, but general consensus is to always use the value from configure.

PYTHON_PLATFORM ¶

The canonical name used by Python to describe the operating system, as given by sys.platform. This value is sometimes needed when building Python extensions.

pythondir ¶

The directory name for the site-packages subdirectory of the standard Python install tree.

pkgpythondir ¶

This is is the directory under pythondir which is named after the package. That is, it is ‘$(pythondir)/$(PACKAGE)’. It is provided as a convenience.

pyexecdir ¶

This is the directory where Python extension modules (shared libraries) should be installed.

pkgpyexecdir ¶

This is a convenience variable which is defined as ‘$(pyexecdir)/$(PACKAGE)’.

All these directory variables have values that start with either ${prefix} or ${exec_prefix} unexpanded. This works fine in Makefiles, but it makes these variables hard to use in configure. This is mandated by the GNU coding standards, so that the user can run make prefix=/foo install. The Autoconf manual has a section with more details on this topic (see Installation Directory Variables in The Autoconf Manual).

10.1 Texinfo

If the current directory contains Texinfo source, you must declare it with the ‘TEXINFOS’ primary. Generally Texinfo files are converted into info, and thus the info_TEXINFOS variable is most commonly used here. Any Texinfo source file must end in the .texi, .txi, or .texinfo extension. We recommend .texi for new manuals.

Automake generates rules to build .info, .dvi, .ps, .pdf and .html files from your Texinfo sources. The .info files are built by make all and installed by make install (unless you use no-installinfo, see below). The other files can be built on request by make dvi, make ps, make pdf and make html.

If the .texi file @includes version.texi, then that file will be automatically generated. The file version.texi defines four Texinfo flag you can reference using @value{EDITION}, @value{VERSION}, @value{UPDATED}, and @value{UPDATED-MONTH}.

EDITION

VERSION

Both of these flags hold the version number of your program. They are kept separate for clarity.

UPDATED

This holds the date the primary .texi file was last modified.

UPDATED-MONTH

This holds the name of the month in which the primary .texi file was last modified.

The version.texi support requires the mdate-sh program; this program is supplied with Automake and automatically included when automake is invoked with the --add-missing option.

If you have multiple Texinfo files, and you want to use the version.texi feature, then you have to have a separate version file for each Texinfo file. Automake will treat any include in a Texinfo file that matches ‘vers*.texi’ just as an automatically generated version file.

Sometimes an info file actually depends on more than one .texi file. For instance, in GNU Hello, hello.texi includes the file gpl.texi. You can tell Automake about these dependencies using the texi_TEXINFOS variable. Here is how GNU Hello does it:

info_TEXINFOS = hello.texi
hello_TEXINFOS = gpl.texi

By default, Automake requires the file texinfo.tex to appear in the same directory as the Texinfo source (this can be changed using the TEXINFO_TEX variable, see below). However, if you used AC_CONFIG_AUX_DIR in configure.ac (see Finding ‘configure’ Input in The Autoconf Manual), then texinfo.tex is looked for there. Automake supplies texinfo.tex if ‘--add-missing’ is given.

The option ‘no-texinfo.tex’ can be used to eliminate the requirement for texinfo.tex. Use of the variable TEXINFO_TEX is preferable, however, because that allows the dvi, ps, and pdf targets to still work.

Automake generates an install-info rule; some people apparently use this. By default, info pages are installed by ‘make install’. This can be prevented via the no-installinfo option.

The following variables are used by the Texinfo build rules.

MAKEINFO ¶

The name of the program invoked to build .info files. This variable is defined by Automake. If the makeinfo program is found on the system then it will be used by default; otherwise missing will be used instead.

MAKEINFOHTML ¶

The command invoked to build .html files. Automake defines this to $(MAKEINFO) --html.

MAKEINFOFLAGS ¶

User flags passed to each invocation of $(MAKEINFO) and $(MAKEINFOHTML). This user variable (see Variables reserved for the user) is not expected to be defined in any Makefile; it can be used by users to pass extra flags to suit their needs.

AM_MAKEINFOFLAGS ¶

AM_MAKEINFOHTMLFLAGS ¶

Maintainer flags passed to each makeinfo invocation. These are maintainer variables that can be overridden in Makefile.am. $(AM_MAKEINFOFLAGS) is passed to makeinfo when building .info files; and $(AM_MAKEINFOHTMLFLAGS) is used when building .html files.

For instance the following setting can be used to obtain one single .html file per manual, without node separators.

AM_MAKEINFOHTMLFLAGS = --no-headers --no-split

By default, $(AM_MAKEINFOHTMLFLAGS) is set to $(AM_MAKEINFOFLAGS). This means that defining $(AM_MAKEINFOFLAGS) without defining $(AM_MAKEINFOHTMLFLAGS) will impact builds of both .info and .html files.

TEXI2DVI ¶

The name of the command that converts a .texi file into a .dvi file. This defaults to texi2dvi, a script that ships with the Texinfo package.

TEXI2PDF ¶

The name of the command that translates a .texi file into a .pdf file. This defaults to $(TEXI2DVI) --pdf --batch.

DVIPS ¶

The name of the command that build a .ps file out of a .dvi file. This defaults to dvips.

TEXINFO_TEX ¶

If your package has Texinfo files in many directories, you can use the variable TEXINFO_TEX to tell Automake where to find the canonical texinfo.tex for your package. The value of this variable should be the relative path from the current Makefile.am to texinfo.tex:

TEXINFO_TEX = ../doc/texinfo.tex

10.2 Man pages

A package can also include man pages (but see the GNU standards on this matter, Man Pages in The GNU Coding Standards.) Man pages are declared using the ‘MANS’ primary. Generally the man_MANS variable is used. Man pages are automatically installed in the correct subdirectory of mandir, based on the file extension.

File extensions such as ‘.1c’ are handled by looking for the valid part of the extension and using that to determine the correct subdirectory of mandir. Valid section names are the digits ‘0’ through ‘9’, and the letters ‘l’ and ‘n’.

Sometimes developers prefer to name a man page something like foo.man in the source, and then rename it to have the correct suffix, e.g. foo.1, when installing the file. Automake also supports this mode. For a valid section named SECTION, there is a corresponding directory named ‘manSECTIONdir’, and a corresponding ‘_MANS’ variable. Files listed in such a variable are installed in the indicated section. If the file already has a valid suffix, then it is installed as-is; otherwise the file suffix is changed to match the section.

For instance, consider this example:

man1_MANS = rename.man thesame.1 alsothesame.1c

In this case, rename.man will be renamed to rename.1 when installed, but the other files will keep their names.

By default, man pages are installed by ‘make install’. However, since the GNU project does not require man pages, many maintainers do not expend effort to keep the man pages up to date. In these cases, the no-installman option will prevent the man pages from being installed by default. The user can still explicitly install them via ‘make install-man’.

Here is how the man pages are handled in GNU cpio (which includes both Texinfo documentation and man pages):

man_MANS = cpio.1 mt.1
EXTRA_DIST = $(man_MANS)

Man pages are not currently considered to be source, because it is not uncommon for man pages to be automatically generated. Therefore they are not automatically included in the distribution. However, this can be changed by use of the ‘dist_’ prefix.

The ‘nobase_’ prefix is meaningless for man pages and is disallowed.

11.1 Basics of installation

Naturally, Automake handles the details of actually installing your program once it has been built. All files named by the various primaries are automatically installed in the appropriate places when the user runs make install.

A file named in a primary is installed by copying the built file into the appropriate directory. The base name of the file is used when installing.

bin_PROGRAMS = hello subdir/goodbye

In this example, both ‘hello’ and ‘goodbye’ will be installed in $(bindir).

Sometimes it is useful to avoid the basename step at install time. For instance, you might have a number of header files in subdirectories of the source tree which are laid out precisely how you want to install them. In this situation you can use the ‘nobase_’ prefix to suppress the base name step. For example:

nobase_include_HEADERS = stdio.h sys/types.h

Will install stdio.h in $(includedir) and types.h in $(includedir)/sys.

11.2 The two parts of install

Automake generates separate install-data and install-exec rules, in case the installer is installing on multiple machines which share directory structure—these targets allow the machine-independent parts to be installed only once. install-exec installs platform-dependent files, and install-data installs platform-independent files. The install target depends on both of these targets. While Automake tries to automatically segregate objects into the correct category, the Makefile.am author is, in the end, responsible for making sure this is done correctly.

Variables using the standard directory prefixes ‘data’, ‘info’, ‘man’, ‘include’, ‘oldinclude’, ‘pkgdata’, or ‘pkginclude’ (e.g. ‘data_DATA’) are installed by ‘install-data’.

Variables using the standard directory prefixes ‘bin’, ‘sbin’, ‘libexec’, ‘sysconf’, ‘localstate’, ‘lib’, or ‘pkglib’ (e.g. ‘bin_PROGRAMS’) are installed by ‘install-exec’.

Any variable using a user-defined directory prefix with ‘exec’ in the name (e.g. ‘myexecbin_PROGRAMS’ is installed by ‘install-exec’. All other user-defined prefixes are installed by ‘install-data’.

11.3 Extending installation

It is possible to extend this mechanism by defining an install-exec-local or install-data-local rule. If these rules exist, they will be run at ‘make install’ time. These rules can do almost anything; care is required.

Automake also supports two install hooks, install-exec-hook and install-data-hook. These hooks are run after all other install rules of the appropriate type, exec or data, have completed. So, for instance, it is possible to perform post-installation modifications using an install hook.

11.4 Staged installs

Automake generates support for the ‘DESTDIR’ variable in all install rules. ‘DESTDIR’ is used during the ‘make install’ step to relocate install objects into a staging area. Each object and path is prefixed with the value of ‘DESTDIR’ before being copied into the install area. Here is an example of typical DESTDIR usage:

mkdir /tmp/staging &&
make DESTDIR=/tmp/staging install

The mkdir command avoids a security problem if the attacker creates a symbolic link from /tmp/staging to a victim area; then make places install objects in a directory tree built under /tmp/staging. If /gnu/bin/foo and /gnu/share/aclocal/foo.m4 are to be installed, the above command would install /tmp/staging/gnu/bin/foo and /tmp/staging/gnu/share/aclocal/foo.m4.

This feature is commonly used to build install images and packages. For more information, see Makefile Conventions in The GNU Coding Standards.

Support for ‘DESTDIR’ is implemented by coding it directly into the install rules. If your Makefile.am uses a local install rule (e.g., install-exec-local) or an install hook, then you must write that code to respect ‘DESTDIR’.

11.5 Rules for the user

Automake also generates rules for targets uninstall, installdirs, and install-strip.

Automake supports uninstall-local and uninstall-hook. There is no notion of separate uninstalls for “exec” and “data”, as these features would not provide additional functionality.

Note that uninstall is not meant as a replacement for a real packaging tool.

13.1 Basics of distribution

The dist rule in the generated Makefile.in can be used to generate a gzip’d tar file and other flavors of archive for distribution. The files is named based on the ‘PACKAGE’ and ‘VERSION’ variables defined by AM_INIT_AUTOMAKE (see Autoconf macros supplied with Automake); more precisely the gzip’d tar file is named ‘package-version.tar.gz’. You can use the make variable ‘GZIP_ENV’ to control how gzip is run. The default setting is ‘--best’.

For the most part, the files to distribute are automatically found by Automake: all source files are automatically included in a distribution, as are all Makefile.ams and Makefile.ins. Automake also has a built-in list of commonly used files which are automatically included if they are found in the current directory (either physically, or as the target of a Makefile.am rule). This list is printed by ‘automake --help’. Also, files which are read by configure (i.e. the source files corresponding to the files specified in various Autoconf macros such as AC_CONFIG_FILES and siblings) are automatically distributed. Files included in Makefile.ams (using include) or in configure.ac (using m4_include), and helper scripts installed with ‘automake --add-missing’ are also distributed.

Still, sometimes there are files which must be distributed, but which are not covered in the automatic rules. These files should be listed in the EXTRA_DIST variable. You can mention files from subdirectories in EXTRA_DIST.

You can also mention a directory in EXTRA_DIST; in this case the entire directory will be recursively copied into the distribution. Please note that this will also copy everything in the directory, including CVS/RCS version control files. We recommend against using this feature.

If you define SUBDIRS, Automake will recursively include the subdirectories in the distribution. If SUBDIRS is defined conditionally (see Conditionals), Automake will normally include all directories that could possibly appear in SUBDIRS in the distribution. If you need to specify the set of directories conditionally, you can set the variable DIST_SUBDIRS to the exact list of subdirectories to include in the distribution (see Conditional Subdirectories).

13.2 Fine-grained distribution control

Sometimes you need tighter control over what does not go into the distribution; for instance you might have source files which are generated and which you do not want to distribute. In this case Automake gives fine-grained control using the ‘dist’ and ‘nodist’ prefixes. Any primary or ‘_SOURCES’ variable can be prefixed with ‘dist_’ to add the listed files to the distribution. Similarly, ‘nodist_’ can be used to omit the files from the distribution.

As an example, here is how you would cause some data to be distributed while leaving some source code out of the distribution:

dist_data_DATA = distribute-this
bin_PROGRAMS = foo
nodist_foo_SOURCES = do-not-distribute.c

13.3 The dist hook

Occasionally it is useful to be able to change the distribution before it is packaged up. If the dist-hook rule exists, it is run after the distribution directory is filled, but before the actual tar (or shar) file is created. One way to use this is for distributing files in subdirectories for which a new Makefile.am is overkill:

dist-hook:
        mkdir $(distdir)/random
        cp -p $(srcdir)/random/a1 $(srcdir)/random/a2 $(distdir)/random

Another way to to use this is for removing unnecessary files that get recursively included by specifying a directory in EXTRA_DIST:

EXTRA_DIST = doc

dist-hook:
	rm -rf `find $(distdir)/doc -name CVS`

Two variables that come handy when writing dist-hook rules are $(distdir) and $(top_distdir).

$(distdir) points to the directory where the dist rule will copy files from the current directory before creating the tarball. If you are at the top-level directory, then distdir = $(PACKAGE)-$(VERSION). When used from subdirectory named foo/, then distdir = ../$(PACKAGE)-$(VERSION)/foo. $(distdir) can be a relative or absolute path, do not assume any form.

$(top_distdir) always points to the root directory of the distributed tree. At the top-level it’s equal to $(distdir). In the foo/ subdirectory top_distdir = ../$(PACKAGE)-$(VERSION). $(top_distdir) too can be a relative or absolute path.

Note that when packages are nested using AC_CONFIG_SUBDIRS (see Nesting Packages), then $(distdir) and $(top_distdir) are relative to the package where make dist was run, not to any sub-packages involved.

13.4 Checking the distribution

Automake also generates a distcheck rule which can be of help to ensure that a given distribution will actually work. distcheck makes a distribution, then tries to do a VPATH build, run the test suite, and finally make another tarfile to ensure the distribution is self-contained.

Building the package involves running ./configure. If you need to supply additional flags to configure, define them in the DISTCHECK_CONFIGURE_FLAGS variable, either in your top-level Makefile.am, or on the command line when invoking make.

If the distcheck-hook rule is defined in your top-level Makefile.am, then it will be invoked by distcheck after the new distribution has been unpacked, but before the unpacked copy is configured and built. Your distcheck-hook can do almost anything, though as always caution is advised. Generally this hook is used to check for potential distribution errors not caught by the standard mechanism. Note that distcheck-hook as well as DISTCHECK_CONFIGURE_FLAGS are not honored in a subpackage Makefile.am, but the DISTCHECK_CONFIGURE_FLAGS are passed down to the configure script of the subpackage.

Speaking about potential distribution errors, distcheck will also ensure that the distclean rule actually removes all built files. This is done by running make distcleancheck at the end of the VPATH build. By default, distcleancheck will run distclean and then make sure the build tree has been emptied by running $(distcleancheck_listfiles). Usually this check will find generated files that you forgot to add to the DISTCLEANFILES variable (see What Gets Cleaned).

The distcleancheck behavior should be OK for most packages, otherwise you have the possibility to override the definition of either the distcleancheck rule, or the $(distcleancheck_listfiles) variable. For instance to disable distcleancheck completely, add the following rule to your top-level Makefile.am:

distcleancheck:
        @:

If you want distcleancheck to ignore built files which have not been cleaned because they are also part of the distribution, add the following definition instead:

distcleancheck_listfiles = \
  find -type f -exec sh -c 'test -f $(srcdir)/{} || echo {}' ';'

The above definition is not the default because it’s usually an error if your Makefiles cause some distributed files to be rebuilt when the user build the package. (Think about the user missing the tool required to build the file; or if the required tool is built by your package, consider the cross-compilation case where it can’t be run.) There is a FAQ entry about this (see Files left in build directory after distclean), make sure you read it before playing with distcleancheck_listfiles.

distcheck also checks that the uninstall rule works properly, both for ordinary and ‘DESTDIR’ builds. It does this by invoking make uninstall, and then it checks the install tree to see if any files are left over. This check will make sure that you correctly coded your uninstall-related rules.

By default, the checking is done by the distuninstallcheck rule, and the list of files in the install tree is generated by $(distuninstallcheck_listfiles) (this is a variable whose value is a shell command to run that prints the list of files to stdout).

Either of these can be overridden to modify the behavior of distcheck. For instance, to disable this check completely, you would write:

distuninstallcheck:
        @:

13.5 The types of distributions

Automake generates rules to provide archives of the project for distributions in various formats. Their targets are:

dist-bzip2

Generate a bzip2 tar archive of the distribution. bzip2 archives are frequently smaller than gzipped archives.

dist-gzip

Generate a gzip tar archive of the distribution.

dist-shar

Generate a shar archive of the distribution.

dist-zip

Generate a zip archive of the distribution.

dist-tarZ

Generate a compressed tar archive of the distribution.

The rule dist (and its historical synonym dist-all) will create archives in all the enabled formats, Changing Automake’s Behavior. By default, only the dist-gzip target is hooked to dist.

14.1 Simple Tests

If the variable TESTS is defined, its value is taken to be a list of programs to run in order to do the testing. The programs can either be derived objects or source objects; the generated rule will look both in srcdir and .. Programs needing data files should look for them in srcdir (which is both an environment variable and a make variable) so they work when building in a separate directory (see Build Directories in The Autoconf Manual), and in particular for the distcheck rule (see What Goes in a Distribution).

The number of failures will be printed at the end of the run. If a given test program exits with a status of 77, then its result is ignored in the final count. This feature allows non-portable tests to be ignored in environments where they don’t make sense.

The variable TESTS_ENVIRONMENT can be used to set environment variables for the test run; the environment variable srcdir is set in the rule. If all your test programs are scripts, you can also set TESTS_ENVIRONMENT to an invocation of the shell (e.g. ‘$(SHELL) -x’); this can be useful for debugging the tests.

You may define the variable XFAIL_TESTS to a list of tests (usually a subset of TESTS) that are expected to fail. This will reverse the result of those tests.

Automake ensures that each program listed in TESTS is built before any tests are run; you can list both source and derived programs in TESTS. For instance, you might want to run a C program as a test. To do this you would list its name in TESTS and also in check_PROGRAMS, and then specify it as you would any other program.

14.2 DejaGnu Tests

If ‘dejagnu’ appears in AUTOMAKE_OPTIONS, then a dejagnu-based test suite is assumed. The variable DEJATOOL is a list of names which are passed, one at a time, as the --tool argument to runtest invocations; it defaults to the name of the package.

The variable RUNTESTDEFAULTFLAGS holds the --tool and --srcdir flags that are passed to dejagnu by default; this can be overridden if necessary.

The variables EXPECT and RUNTEST can also be overridden to provide project-specific values. For instance, you will need to do this if you are testing a compiler toolchain, because the default values do not take into account host and target names.

The contents of the variable RUNTESTFLAGS are passed to the runtest invocation. This is considered a “user variable” (see Variables reserved for the user). If you need to set runtest flags in Makefile.am, you can use AM_RUNTESTFLAGS instead.

Automake will generate rules to create a local site.exp file, defining various variables detected by ./configure. This file is automatically read by DejaGnu. It is OK for the user of a package to edit this file in order to tune the test suite. However this is not the place where the test suite author should define new variables: this should be done elsewhere in the real test suite code. Especially, site.exp should not be distributed.

For more information regarding DejaGnu test suites, see See The DejaGnu Manual.

In either case, the testing is done via ‘make check’.

14.3 Install Tests

The installcheck target is available to the user as a way to run any tests after the package has been installed. You can add tests to this by writing an installcheck-local rule.

17.1 Interfacing to etags

Automake will generate rules to generate TAGS files for use with GNU Emacs under some circumstances.

If any C, C++ or Fortran 77 source code or headers are present, then tags and TAGS rules will be generated for the directory. All files listed using the _SOURCES, _HEADERS, and _LISP primaries will be used to generate tags. Note that generated source files that are not distributed must be declared in variables like nodist_noinst_HEADERS or nodist_prog_SOURCES or they will be ignored.

At the topmost directory of a multi-directory package, a tags rule will be output which, when run, will generate a TAGS file that includes by reference all TAGS files from subdirectories.

The tags rule will also be generated if the variable ETAGS_ARGS is defined. This variable is intended for use in directories which contain taggable source that etags does not understand. The user can use the ETAGSFLAGS to pass additional flags to etags; AM_ETAGSFLAGS is also available for use in Makefile.am.

Here is how Automake generates tags for its source, and for nodes in its Texinfo file:

ETAGS_ARGS = automake.in --lang=none \
 --regex='/^@node[ \t]+\([^,]+\)/\1/' automake.texi

If you add filenames to ‘ETAGS_ARGS’, you will probably also want to set ‘TAGS_DEPENDENCIES’. The contents of this variable are added directly to the dependencies for the tags rule.

Automake also generates a ctags rule which can be used to build vi-style tags files. The variable CTAGS is the name of the program to invoke (by default ‘ctags’); CTAGSFLAGS can be used by the user to pass additional flags, and AM_CTAGSFLAGS can be used by the Makefile.am.

Automake will also generate an ID rule which will run mkid on the source. This is only supported on a directory-by-directory basis.

Automake also supports the GNU Global Tags program. The GTAGS rule runs Global Tags automatically and puts the result in the top build directory. The variable GTAGS_ARGS holds arguments which are passed to gtags.

17.2 Handling new file extensions

It is sometimes useful to introduce a new implicit rule to handle a file type that Automake does not know about.

For instance, suppose you had a compiler which could compile ‘.foo’ files to ‘.o’ files. You would simply define an suffix rule for your language:

.foo.o:
        foocc -c -o $@ $<

Then you could directly use a ‘.foo’ file in a ‘_SOURCES’ variable and expect the correct results:

bin_PROGRAMS = doit
doit_SOURCES = doit.foo

This was the simpler and more common case. In other cases, you will have to help Automake to figure which extensions you are defining your suffix rule for. This usually happens when your extensions does not start with a dot. Then, all you have to do is to put a list of new suffixes in the SUFFIXES variable before you define your implicit rule.

For instance the following definition prevents Automake to misinterpret ‘.idlC.cpp:’ as an attempt to transform ‘.idlC’ into ‘.cpp’.

SUFFIXES = .idl C.cpp
.idlC.cpp:
        # whatever

As you may have noted, the SUFFIXES variable behaves like the .SUFFIXES special target of make. You should not touch .SUFFIXES yourself, but use SUFFIXES instead and let Automake generate the suffix list for .SUFFIXES. Any given SUFFIXES go at the start of the generated suffixes list, followed by Automake generated suffixes not already in the list.

17.3 Support for Multilibs

Automake has support for an obscure feature called multilibs. A multilib is a library which is built for multiple different ABIs at a single time; each time the library is built with a different target flag combination. This is only useful when the library is intended to be cross-compiled, and it is almost exclusively used for compiler support libraries.

The multilib support is still experimental. Only use it if you are familiar with multilibs and can debug problems you might encounter.

22.1 Extending Automake Rules

With some minor exceptions (like _PROGRAMS variables being rewritten to append $(EXEEXT)), the contents of a Makefile.am is copied to Makefile.in verbatim.

These copying semantics means that many problems can be worked around by simply adding some make variables and rules to Makefile.am. Automake will ignore these additions.

Since a Makefile.in is built from data gathered from three different places (Makefile.am, configure.ac, and automake itself), it is possible to have conflicting definitions of rules or variables. When building Makefile.in the following priorities are respected by automake to ensure the user always have the last word. User defined variables in Makefile.am have priority over variables AC_SUBSTed from configure.ac, and AC_SUBSTed variables have priority over automake-defined variables. As far rules are concerned, a user-defined rule overrides any automake-defined rule for the same target.

These overriding semantics make it possible to fine tune some default settings of Automake, or replace some of its rules. Overriding Automake rules is often inadvisable, particularly in the topmost directory of a package with subdirectories. The -Woverride option (see Creating a Makefile.in) comes handy to catch overridden definitions.

Note that Automake does not make any difference between rules with commands and rules that only specify dependencies. So it is not possible to append new dependencies to an automake-defined target without redefining the entire rule.

However, various useful targets have a ‘-local’ version you can specify in your Makefile.in. Automake will supplement the standard target with these user-supplied targets.

The targets that support a local version are all, info, dvi, ps, pdf, html, check, install-data, install-exec, uninstall, installdirs, installcheck and the various clean targets (mostlyclean, clean, distclean, and maintainer-clean). Note that there are no uninstall-exec-local or uninstall-data-local targets; just use uninstall-local. It doesn’t make sense to uninstall just data or just executables.

For instance, here is one way to install a file in /etc:

install-data-local:
        $(INSTALL_DATA) $(srcdir)/afile $(DESTDIR)/etc/afile

Some rule also have a way to run another rule, called a hook, after their work is done. The hook is named after the principal target, with ‘-hook’ appended. The targets allowing hooks are install-data, install-exec, uninstall, dist, and distcheck.

For instance, here is how to create a hard link to an installed program:

install-exec-hook:
        ln $(DESTDIR)$(bindir)/program$(EXEEXT) \
           $(DESTDIR)$(bindir)/proglink$(EXEEXT)

Although cheaper and more portable than symbolic links, hard links will not work everywhere (for instance OS/2 does not have ln). Ideally you should fall back to cp -p when ln does not work. An easy way, if symbolic links are acceptable to you, is to add AC_PROG_LN_S to configure.ac (see Particular Program Checks in The Autoconf Manual) and use $(LN_S) in Makefile.am.

For instance, here is how you could install a versioned copy of a program using $(LN_S):

install-exec-hook:
        cd $(DESTDIR)$(bindir) && \
          mv -f prog$(EXEEXT) prog-$(VERSION)$(EXEEXT) && \
          $(LN_S) prog-$(VERSION)$(EXEEXT) prog$(EXEEXT)

Note that we rename the program so that a new version will erase the symbolic link, not the real binary. Also we cd into the destination directory in order to create relative links.

22.2 Third-Party Makefiles

In most projects all Makefiles are generated by Automake. In some cases, however, projects need to embed subdirectories with handwritten Makefiles. For instance one subdirectory could be a third-party project with its own build system, not using Automake.

It is possible to list arbitrary directories in SUBDIRS or DIST_SUBDIRS provided each of these directories has a Makefile that recognizes all the following recursive targets.

When a user runs one of these targets, that target is run recursively in all subdirectories. This is why it is important that even third-party Makefiles support them.

all

Compile the entire package. This is the default target in Automake-generated Makefiles, but it does not need to be the default in third-party Makefiles.

distdir ¶

Copy files to distribute into $(distdir), before a tarball is constructed. Of course this target is not required if the no-dist option (see Changing Automake’s Behavior) is used.

The variables $(top_distdir) and $(distdir) (see What Goes in a Distribution) will be passed from the outer package to the subpackage when the distdir target is invoked. These two variables have been adjusted for the directory which is being recursed into, so they are ready to use.

install

install-data

install-exec

uninstall

Install or uninstall files (see What Gets Installed).

install-info

Install only the Texinfo documentation (see Texinfo).

installdirs

Create install directories, but do not install any files.

check

installcheck

Check the package (see Support for test suites).

mostlyclean

clean

distclean

maintainer-clean

Cleaning rules (see What Gets Cleaned).

dvi

pdf

ps

info

html

Build the documentation in various formats (see Texinfo).

tags

ctags

Build TAGS and CTAGS (see Interfacing to etags).

If you have ever used Gettext in a project, this is a good example of how third-party Makefiles can be used with Automake. The Makefiles gettextize puts in the po/ and intl/ directories are handwritten Makefiles that implement all these targets. That way they can be added to SUBDIRS in Automake packages.

Directories which are only listed in DIST_SUBDIRS but not in SUBDIRS need only the distclean, maintainer-clean, and distdir rules (see Conditional Subdirectories).

Usually, many of these rules are irrelevant to the third-party subproject, but they are required for the whole package to work. It’s OK to have a rule that does nothing, so if you are integrating a third-party project with no documentation or tag support, you could simply augment its Makefile as follows:

EMPTY_AUTOMAKE_TARGETS = dvi pdf ps info html tags ctags
.PHONY: $(EMPTY_AUTOMAKE_TARGETS)
$(EMPTY_AUTOMAKE_TARGETS):

Another aspect of integrating third-party build systems is whether they support VPATH builds. Obviously if the subpackage does not support VPATH builds the whole package will not support VPATH builds. This in turns means that make distcheck will not work, because it relies on VPATH builds. Some people can live without this (actually, many Automake users have never heard of make distcheck). Other people may prefer to revamp the existing Makefiles to support VPATH. Doing so does not necessarily require Automake, only Autoconf is needed (see Build Directories in The Autoconf Manual). The necessary substitutions: @scrdir@, @top_srcdir@, and @top_buildir@ are defined by configure when it processes a Makefile (see Preset Output Variables in The Autoconf Manual), they are not computed by the Makefile like the aforementioned $(distdir) and $(top_distdir) variables..

It is sometimes inconvenient to modify a third-party Makefile to introduce the above required targets. For instance one may want to keep the third-party sources untouched to ease upgrades to new versions.

Here are two other ideas. If GNU make is assumed, one possibility is to add to that subdirectory a GNUmakefile that defines the required targets and include the third-party Makefile. For this to work in VPATH builds, GNUmakefile must lie in the build directory; the easiest way to do this is to write a GNUmakefile.in instead, and have it processed with AC_CONFIG_FILES from the outer package. For example if we assume Makefile defines all targets except the documentation targets, and that the check target is actually called test, we could write GNUmakefile (or GNUmakefile.in) like this:

# First, include the real Makefile
include Makefile
# Then, define the other targets needed by Automake Makefiles.
.PHONY: dvi pdf ps info html check
dvi pdf ps info html:
check: test

A similar idea that does not use include is to write a proxy Makefile that dispatches rules to the real Makefile, either with $(MAKE) -f Makefile.real $(AM_MAKEFLAGS) target (if it’s OK to rename the original Makefile) or with cd subdir && $(MAKE) $(AM_MAKEFLAGS) target (if it’s OK to store the subdirectory project one directory deeper). The good news is that this proxy Makefile can be generated with Automake. All we need are -local targets (see Extending Automake Rules) that perform the dispatch. Of course the other Automake features are available, so you could decide to let Automake perform distribution or installation. Here is a possible Makefile.am:

all-local:
        cd subdir && $(MAKE) $(AM_MAKEFLAGS) all
check-local:
        cd subdir && $(MAKE) $(AM_MAKEFLAGS) test
clean-local:
        cd subdir && $(MAKE) $(AM_MAKEFLAGS) clean

# Assuming the package knows how to install itself
install-data-local:
        cd subdir && $(MAKE) $(AM_MAKEFLAGS) install-data
install-exec-local:
        cd subdir && $(MAKE) $(AM_MAKEFLAGS) install-exec
uninstall-local:
        cd subdir && $(MAKE) $(AM_MAKEFLAGS) uninstall

# Distribute files from here.
EXTRA_DIST = subdir/Makefile subdir/program.c ...

Pushing this idea to the extreme, it is also possible to ignore the subproject build system and build everything from this proxy Makefile.am. This might sounds very sensible if you need VPATH builds but the subproject does not support them.

26.1 CVS and generated files

• Background: distributed generated files
• Background: CVS and timestamps
• Living with CVS in Autoconfiscated projects
• Third-party files

26.2 missing and AM_MAINTAINER_MODE

• missing
• AM_MAINTAINER_MODE

26.3 Why doesn’t Automake support wildcards?

Developers are lazy. They often would like to use wildcards in Makefile.ams, so they don’t need to remember they have to update Makefile.ams every time they add, delete, or rename a file.

There are several objections to this:

• When using CVS (or similar) developers need to remember they have to run cvs add or cvs rm anyway. Updating Makefile.am accordingly quickly becomes a reflex.

  Conversely, if your application doesn’t compile because you forgot to add a file in Makefile.am, it will help you remember to cvs add it.

• Using wildcards makes easy to distribute files by mistake. For instance some code a developer is experimenting with (a test case, say) but which should not be part of the distribution.
• Using wildcards it’s easy to omit some files by mistake. For instance one developer creates a new file, uses it at many places, but forget to commit it. Another developer then checkout the incomplete project and is able to run ‘make dist’ successfully, even though a file is missing.
• Listing files, you control *exactly* what you distribute. If some file that should be distributed is missing from your tree, make dist will complain. Besides, you don’t distribute more than what you listed.
• Finally it’s really hard to forget adding a file to Makefile.am, because if you don’t add it, it doesn’t get compiled nor installed, so you can’t even test it.

Still, these are philosophical objections, and as such you may disagree, or find enough value in wildcards to dismiss all of them. Before you start writing a patch against Automake to teach it about wildcards, let’s see the main technical issue: portability.

Although $(wildcard ...) works with GNU make, it is not portable to other make implementations.

The only way Automake could support $(wildcard ...) is by expending $(wildcard ...) when automake is run. Resulting Makefile.ins would be portable since they would list all files and not use $(wildcard ...). However that means developers need to remember they must run automake each time they add, delete, or rename files.

Compared to editing Makefile.am, this is really little win. Sure, it’s easier and faster to type automake; make than to type emacs Makefile.am; make. But nobody bothered enough to write a patch add support for this syntax. Some people use scripts to generated file lists in Makefile.am or in separate Makefile fragments.

Even if you don’t care about portability, and are tempted to use $(wildcard ...) anyway because you target only GNU Make, you should know there are many places where Automake need to know exactly which files should be processed. As Automake doesn’t know how to expand $(wildcard ...), you cannot use it in these places. $(wildcard ...) is a black box comparable to AC_SUBSTed variables as far Automake is concerned.

You can get warnings about $(wildcard ...) constructs using the -Wportability flag.

26.4 Files left in build directory after distclean

This is a diagnostic you might encounter while running make distcheck.

As explained in What Goes in a Distribution, make distcheck attempts to build and check your package for errors like this one.

make distcheck will perform a VPATH build of your package, and then call make distclean. Files left in the build directory after make distclean has run are listed after this error.

This diagnostic really covers two kinds of errors:

• files that are forgotten by distclean;
• distributed files that are erroneously rebuilt.

The former left-over files are not distributed, so the fix is to mark them for cleaning (see What Gets Cleaned), this is obvious and doesn’t deserve more explanations.

The latter bug is not always easy to understand and fix, so let’s proceed with an example. Suppose our package contains a program for which we want to build a man page using help2man. GNU help2man produces simple manual pages from the --help and --version output of other commands (see Overview in The Help2man Manual). Because we don’t to force want our users to install help2man, we decide to distribute the generated man page using the following setup.

# This Makefile.am is bogus.
bin_PROGRAMS = foo
foo_SOURCES = foo.c
dist_man_MANS = foo.1

foo.1: foo$(EXEEXT)
	help2man --output=foo.1 ./foo$(EXEEXT)

This will effectively distribute the man page. However, make distcheck will fail with:

ERROR: files left in build directory after distclean:
./foo.1

Why was foo.1 rebuilt? Because although distributed, foo.1 depends on a non-distributed built file: foo$(EXEEXT). foo$(EXEEXT) is built by the user, so it will always appear to be newer than the distributed foo.1.

make distcheck caught an inconsistency in our package. Our intent was to distribute foo.1 so users do not need installing help2man, however since this our rule causes this file to be always rebuilt, users do need help2man. Either we should ensure that foo.1 is not rebuilt by users, or there is no point in distributing foo.1.

More generally, the rule is that distributed files should never depend on non-distributed built files. If you distribute something generated, distribute its sources.

One way to fix the above example, while still distributing foo.1 is to not depend on foo$(EXEEXT). For instance, assuming foo --version and foo --help do not change unless foo.c or configure.ac change, we could write the following Makefile.am:

bin_PROGRAMS = foo
foo_SOURCES = foo.c
dist_man_MANS = foo.1

foo.1: foo.c $(top_srcdir)/configure.ac
        $(MAKE) $(AM_MAKEFLAGS) foo$(EXEEXT)
	help2man --output=foo.1 ./foo$(EXEEXT)

This way, foo.1 will not get rebuilt every time foo$(EXEEXT) changes. The make call makes sure foo$(EXEEXT) is up-to-date before help2man. Another way to ensure this would be to use separate directories for binaries and man pages, and set SUBDIRS so that binaries are built before man pages.

We could also decide not to distribute foo.1. In this case it’s fine to have foo.1 dependent upon foo$(EXEEXT), since both will have to be rebuilt. However it would be impossible to build the package in a cross-compilation, because building foo.1 involves an execution of foo$(EXEEXT).

Another context where such errors are common is when distributed files are built by tools which are built by the package. The pattern is similar:

distributed-file: built-tools distributed-sources
        build-command

should be changed to

distributed-file: distributed-sources
        $(MAKE) $(AM_MAKEFLAGS) built-tools
        build-command

or you could choose not to distribute distributed-file, if cross-compilation does not matter.

The points made through these examples are worth a summary:

For desperate cases, it’s always possible to disable this check by setting distcleancheck_listfiles as documented in What Goes in a Distribution. Make sure you do understand the reason why make distcheck complains before you do this. distcleancheck_listfiles is a way to hide errors, not to fix them. You can always do better.

26.5 Why are object files sometimes renamed?

This happens when per-target compilation flags are used. Object files need to be renamed just in case they would clash with object files compiled from the same sources, but with different flags. Consider the following example.

bin_PROGRAMS = true false
true_SOURCES = generic.c
true_CPPFLAGS = -DEXIT_CODE=0
false_SOURCES = generic.c
false_CPPFLAGS = -DEXIT_CODE=1

Obviously the two programs are built from the same source, but it would be bad if they shared the same object, because generic.o cannot be built with both -DEXIT_CODE=0 *and* -DEXIT_CODE=1. Therefore automake outputs rules to build two different objects: true-generic.o and false-generic.o.

automake doesn’t actually look whether sources files are shared to decide if it must rename objects. It will just rename all objects of a target as soon as it sees per-target compilation flags are used.

It’s OK to share object files when per-target compilation flags are not used. For instance true and false will both use version.o in the following example.

AM_CPPFLAGS = -DVERSION=1.0
bin_PROGRAMS = true false
true_SOURCES = true.c version.c
false_SOURCES = false.c version.c

Note that the renaming of objects is also affected by the _SHORTNAME variable (see Program and Library Variables).

26.6 Handling Tools that Produce Many Outputs

This section describes a make idiom that can be used when a tool produces multiple output files. It is not specific to Automake and can be used in ordinary Makefiles.

Suppose we have a program called foo that will read one file called data.foo and produce two files named data.c and data.h. We want to write a Makefile rule that captures this one-to-two dependency.

The naive rule is incorrect:

# This is incorrect.
data.c data.h: data.foo
        foo data.foo

What the above rule really says is that data.c and data.h each depend on data.foo, and can each be built by running foo data.foo. In other words it is equivalent to:

# We do not want this.
data.c: data.foo
        foo data.foo
data.h: data.foo
        foo data.foo

which means that foo can be run twice. Usually it will not be run twice, because make implementations are smart enough to check for the existence of the second file after the first one has been built; they will therefore detect that it already exists. However there are a few situations where it can run twice anyway:

• The most worrying case is when running a parallel make. If data.c and data.h are built in parallel, two foo data.foo commands will run concurrently. This is harmful.
• Another case is when the dependency (here data.foo) is (or depends upon) a phony target.

A solution that works with parallel make but not with phony dependencies is the following:

data.c data.h: data.foo
        foo data.foo
data.h: data.c

The above rules are equivalent to

data.c: data.foo
        foo data.foo
data.h: data.foo data.c
        foo data.foo

therefore a parallel make will have to serialize the builds of data.c and data.h, and will detect that the second is no longer needed once the first is over.

Using this pattern is probably enough for most cases. However it does not scale easily to more output files (in this scheme all output files must be totally ordered by the dependency relation), so we will explore a more complicated solution.

Another idea is to write the following:

# There is still a problem with this one.
data.c: data.foo
        foo data.foo
data.h: data.c

The idea is that foo data.foo is run only when data.c needs to be updated, but we further state that data.h depends upon data.c. That way, if data.h is required and data.foo is out of date, the dependency on data.c will trigger the build.

This is almost perfect, but suppose we have built data.h and data.c, and then we erase data.h. Then, running make data.h will not rebuild data.h. The above rules just state that data.c must be up-to-date with respect to data.foo, and this is already the case.

What we need is a rule that forces a rebuild when data.h is missing. Here it is:

data.c: data.foo
        foo data.foo
data.h: data.c
        @if test -f $@; then :; else \
          rm -f data.c; \
          $(MAKE) $(AM_MAKEFLAGS) data.c; \
        fi

The above scales easily to more outputs and more inputs. One of the output is picked up to serve as a witness of the run of the command, it depends upon all inputs, and all other outputs depend upon it. For instance if foo should additionally read data.bar and also produce data.w and data.x, we would write:

data.c: data.foo data.bar
        foo data.foo data.bar
data.h data.w data.x: data.c
        @if test -f $@; then :; else \
          rm -f data.c; \
          $(MAKE) $(AM_MAKEFLAGS) data.c; \
        fi

There is still a minor problem with this setup. foo outputs four files, but we do not know in which order these files are created. Suppose that data.h is created before data.c. Then we have a weird situation. The next time make is run, data.h will appear older than data.c, the second rule will be triggered, a shell will be started to execute the if...fi command, but actually it will just execute the then branch, that is: nothing. In other words, because the witness we selected is not the first file created by foo, make will start a shell to do nothing each time it is run.

A simple riposte is to fix the timestamps when this happens.

data.c: data.foo data.bar
        foo data.foo data.bar
data.h data.w data.x: data.c
        @if test -f $@; then \
          touch $@; \
        else \
          rm -f data.c; \
          $(MAKE) $(AM_MAKEFLAGS) data.c; \
        fi

Another solution, not incompatible with the previous one, is to use a different and dedicated file as witness, rather than using any of foo’s outputs.

data.stamp: data.foo data.bar
        @rm -f data.tmp
        @touch data.tmp
        foo data.foo data.bar
        @mv -f data.tmp $@
data.c data.h data.w data.x: data.stamp
        @if test -f $@; then \
          touch $@; \
        else \
          rm -f data.stamp; \
          $(MAKE) $(AM_MAKEFLAGS) data.stamp; \
        fi

data.tmp is created before foo is run, so it has a timestamp older than output files output by foo. It is then renamed to data.stamp after foo has run, because we do not want to update data.stamp if foo fails.

Using a dedicated witness like this is very handy when the list of output files is not known beforehand. As an illustration, consider the following rules to compile many *.el files into *.elc files in a single command. It does not matter how ELFILES is defined (as long as it is not empty: empty targets are not accepted by POSIX).

ELFILES = one.el two.el three.el …
ELCFILES = $(ELFILES:=c)

elc-stamp: $(ELFILES)
        @rm -f elc-temp
        @touch elc-temp
        $(elisp_comp) $(ELFILES)
        @mv -f elc-temp $@

$(ELCFILES): elc-stamp
        @if test -f $@; then \
          touch $@; \
        else \
          rm -f elc-stamp; \
          $(MAKE) $(AM_MAKEFLAGS) elc-stamp; \
        fi

For completeness it should be noted that GNU make is able to express rules with multiple output files using pattern rules (see Pattern Rule Examples in The GNU Make Manual). We do not discuss pattern rules here because they are not portable, but they can be convenient in packages that assume GNU make.