5.1 User -Provided Input Files
The smallest project requires the user to provide only two files. The remainder of the files needed to build the package are generated by the GNU Autotools (see section 5.2 Generated Output Files).
- `Makefile.am' is an input to
- `configure.in' is an input to
I like to think of `Makefile.am' as a high-level, bare-bones specification of a project's build requirements: what needs to be built, and where does it go when it is installed? This is probably Automake's greatest strength--the description is about as simple as it could possibly be, yet the final product is a `Makefile' with an array of convenient
The `configure.in' is a template of macro invocations and shell code fragments that are used by
autoconf to produce a `configure' script (see section C. Generated File Dependencies).
autoconf copies the contents of `configure.in' to `configure' , expanding macros as they occur in the input. Other text is copied verbatim.
Let's take a look at the contents of the user-provided input files that are relevant to this minimal project. Here is the `Makefile.am' :
| || |
bin_PROGRAMS = foonly foonly_SOURCES = main.c foo.c foo.h nly.c scanner.l parser.y foonly_LDADD = @LEXLIB@
This `Makefile.am' specifies that we want a program called `foonly' to be built and installed in the `bin' directory when
make install is run. The source files that are used to build `foonly' are the C source files `main.c' , `foo.c' , `nly.c' and `foo.h' , the
lex program in `scanner.l' and a
yacc grammar in `parser.y' . This points out a particularly nice aspect about Automake: because
yacc both generate intermediate C programs from their input files, Automake knows how to build such intermediate files and link them into the final executable. Finally, we must remember to link a suitable
lex library, if `configure' concludes that one is needed.
And here is the `configure.in' :
| || |
dnl Process this file with autoconf to produce a configure script. AC_INIT(main.c) AM_INIT_AUTOMAKE(foonly, 1.0) AC_PROG_CC AM_PROG_LEX AC_PROG_YACC AC_OUTPUT(Makefile)
This `configure.in' invokes some mandatory Autoconf and Automake initialization macros, and then calls on some Autoconf macros from the
AC_PROG family to find suitable C compiler,
lex , and
yacc programs. Finally, the
AC_OUTPUT macro is used to cause the generated `configure' script to output a `Makefile' ---but from what? It is processed from `Makefile.in' , which Automake produces for you based on your `Makefile.am' (see section C. Generated File Dependencies).