The autoheader2.13 program can create a template file of C #define statements for configure to use. If configure.in invokes AC_CONFIG_HEADER(FILE), autoheader2.13 creates FILE.in; if multiple file arguments are given, the first one is used. Otherwise, autoheader2.13 creates config.h.in.
If you give autoheader2.13 an argument, it uses that file instead of configure.in and writes the header file to the standard output instead of to config.h.in. If you give autoheader2.13 an argument of -, it reads the standard input instead of configure.in and writes the header file to the standard output.
autoheader2.13 scans configure.in and figures out which C preprocessor symbols it might define. It copies comments and #define and #undef statements from a file called acconfig.h, which comes with and is installed with Autoconf. It also uses a file called acconfig.h in the current directory, if present. If you AC_DEFINE any additional symbols, you must create that file with entries for them. For symbols defined by AC_CHECK_HEADERS, AC_CHECK_FUNCS, AC_CHECK_SIZEOF, or AC_CHECK_LIB, autoheader2.13 generates comments and #undef statements itself rather than copying them from a file, since the possible symbols are effectively limitless.
The file that autoheader2.13 creates contains mainly #define and #undef statements and their accompanying comments. If ./acconfig.h contains the string @TOP@, autoheader2.13 copies the lines before the line containing @TOP@ into the top of the file that it generates. Similarly, if ./acconfig.h contains the string @BOTTOM@, autoheader2.13 copies the lines after that line to the end of the file it generates. Either or both of those strings may be omitted.
An alternate way to produce the same effect is to create the files FILE.top (typically config.h.top) and/or FILE.bot in the current directory. If they exist, autoheader2.13 copies them to the beginning and end, respectively, of its output. Their use is discouraged because they have file names that contain two periods, and so can not be stored on MS-DOS; also, they are two more files to clutter up the directory. But if you use the --localdir=DIR option to use an acconfig.h in another directory, they give you a way to put custom boilerplate in each individual config.h.in.
autoheader2.13 accepts the following options:
Print a summary of the command line options and exit.
Look for the package files aclocal.m4 and acconfig.h (but not FILE.top and FILE.bot) in directory DIR instead of in the current directory.
Look for the installed macro files and acconfig.h in directory DIR. You can also set the AC_MACRODIR environment variable to a directory; this option overrides the environment variable.