If the make-like target syntax is ignored, an Automake input file looks like a series of assignments to structured variables:
variable = item ...
where the list of items actually is tokenized as if it were on a shell command line, with quotes and limited variable substitution; configure-time substution is introduced with a strudel (at-sign) character. Some examples:
common_subs = foo.c bar.c
bin_PROGRAMS = polly
polly_SOURCES = main.c $common_subs
polly_CPPFLAGS = -DSUBST="string with spaces"
polly_CFLAGS = -O
polly_LIBADD = curses @EXTRALIBS@
SUBDIRS = src

The variable is cracked right to left, breaking at underscores. There are three flavors: Primary targets : * The first value is one of PROGRAMS, LIBRARIES, LTLIBRARIES, SCRIPTS, DATA, HEADERS, MANS, TEXINFOS, LISP, PYTHON, or JAVA. * The second value is either the keyword EXTRA, the keyword check, or a directory identifier. A directory identifier refers to an Automake variable with dir appended to the name; thus if there's an Automake variable with the name foodir (presumably containing a directory path) then foo is the directory identifier that specifies that path. * There are some predefined directory identifiers (and corresponding variables): bin, data, doc, include, info, lib, libexec, localstate, man, oldinclude, pkgdata, pkginclude, pkglib, sbin, sharedstate, and sysconf. (I may have missed some.) * Other directory identifiers are set up by standard Automake macros: lisp, python, pkgpython, pyexec, and pkgpyexec. * The user may also set up a variable ending in dir and use the associated directory identifier. * The third, fourth, and fifth values are optional prefixes from the set inst, noinst, dist, nodist, and nobase.

Per-target modifiers : * The first value is one of AR, CCASFLAGS, CFLAGS, CPPFLAGS, CXXFLAGS, DEPENDENCIES, FFLAGS, GCJFLAGS, LDADD, LDFLAGS, LFLAGS, LIBADD, LINK, OBJCFLAGS, RFLAGS, SHORTNAME, SOURCES, UPCFLAGS, or YFLAGS. (It's not clear if this set is extensible, or if I missed any.) * The next value is either the keyword AM or an item identified in a primary assignment. The item name is canonicalized. Since the canonical name is created by replacing characters with underscores, teasing out the boundary of the name can be tricky. * The third, fourth, and fifth values are optional prefixes from the set inst, noinst, dist, nodist, and nobase.

Simple variables : Anything not covered by the above cases is a simple variable. Some variables have semantics associated with them (e.g., SUBDIRS says which subdirectories should be examined for further build instructions). There are variables like EXTRA_SOURCES that look like they ought to be one of the first two categories, but have their own semantics. (((There should be a list here of the simple variables with special semantics.)))

• Some combinations of structured variable names are meaningless and are disallowed. For example, PROGRAMS can't be installed in a man directory, and inst and noinst can't both occur as prefixes.

• Many simple variables aren't so simple and have their own specialized semantics. There needs to be a list of some of them here.

  • Although it looks like a primary with a directory identifier, EXTRA_DIST is a simple variable with primary-like semantics.
  • SUBDIRS is a list of subdirectories containing Makefile.am files that are to be included in the build.

• The Makefile.in resulting from an Automake run has a bazillion targets: all, install, install-strip, install-exec, install-data, (,install-) for [man, dvi, html, info, ps, pdf], uninstall, test, dist (and dist-* for [bzip2, gzip, shar, tarZ, zip]), distdir, check, distcheck, installcheck, doc, tags and ctags, clean, mostlyclean, distclean, realclean, maintainer-clean, clobber, and their *-local and *-hook variants. And this list isn't complete. This grid identifies what I believe to be the install locations for each primary type. (Automake probably allows more combinations; if you know of any, please let me know and I'll update it.) It's a useful checklist to ensure minimal coverage of the concepts. It's been extended to include additional SCons builders that don't seem to be included in the list of Automake primaries and for additional install locations that are implied but not specifically mentioned.

• • SCons Builders and additional directories
    E - Executable, platform-specific
    e - Executable
    P - Platform-specific
    S - Single-machine information
    X - Architecture-independent [[!table header="no" class="mointable" data=""" Primary
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l | Notes bin | E | | | | | e | | | | | | | | | | | | |
sbin | E | | | | | e | | | | | | | | | | | | |
libexec | E | | | | | e | | | | | | | | | | | | |
*pkglibexec | E | | | | | e | | | | | | | | | | | | |
lib | | P | P | P | P | | | | | | | | | | | | | |
pkglib | | P | P | P | P | | | | | | | | | | | | | |
data | | | | | | | X | | | | | | | | | | | |
pkgdata | | | | | | | X | | | | X | X | X | X | | | | |
doc | | | | | | | | | | | X | X | X | X | | | | |
include | | | | | | | | X | | | | | | | | | | |
pkginclude | | | | | | | | X | | | | | | | | | | |
oldinclude | | | | | | | | X | | | | | | | | | | |
info | | | | | | | | | | X | | | | | | | | |
man | | | | | | | | | X | | | | | | | | | |
sysconf | | | | | | e | S | | | | | | | | | | | |
*pkgsysconf | | | | | | e | S | | | | | | | | | | | |
localstate | | | | | | | S | | | | | | | | | | | | writable *pkglocalstate | | | | | | | S | | | | | | | | | | | | writable sharedstate | | | | | | | X | | | | | | | | | | | | writable *pkgsharedstate | | | | | | | X | | | | | | | | | | | | writable Directories inserted by associated Builder?|||||||||||||||||||| lisp | | | | | | | | | | | | | | | X | | | |
python | | | | | | | | | | | | | | | | X | | |
pkgpython | | | | | | | | | | | | | | | | X | | |
pyexec | | | | | | | | | | | | | | | | X | | |
pkgpyexec | | | | | | | | | | | | | | | | X | | |
*java | | | | | | | | | | | | | | | | | ? | | ??? """]]