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AX_DEFINE_SUB_PATH(DEFNAME, varname, description)


Look at varname and detect the subpath that it contains relative to $prefix/$exec_prefix. If the path is indeed relative to $prefix/$exec_prefix, then a single "./" (dotslash) is prepended, otherwise it can be seen as an absolute path that cannot be moved, which you possibly do for "/etc" files, or even those ending up in "/lib/modules" or "/winnt/system".

This macro is not very intelligent, it’s just a first try in this direction. It does currently just look into the current patterns, and replaces a ${prefix} with a simple dot. Amazingly, it works quite well for most packages.

Example (

   AX_DEFINE_DIR([EPREFIX], [exec_prefix], [--exec-prefix or default])
  AX_DEFINE_SUB_PATH([PATH_LIBDIR], [libdir], [--bindir subdir])

Example (in C):

   static const char _libdir[] = PATH_LIBDIR; /* configure default */
  char* libdir;
  char* eprefix = getenv (PACKAGE "DIR");
  if (! eprefix) eprefix = EPREFIX; /* default */
  if (*_libdir != '.') libdir = strdup(_libdir);
  else {
     libdir = malloc(strlen(eprefix) + strlen(_libdir) + 2);
     strcpy(libdir, eprefix);
     strcat(libdir, PATH_DELIMITER_STRING);
     strcat(libdir, _libdir);
  free (libdir);

The AX_DEFINE_SUB_PATHS(varnames) macro looks for the given various install-paths that largely depend on either ${prefix} or ${exec_prefix}. Just cut out the prefix and ac_define the value. The value is uppercased and PATH_ prepended ie. ax_define_sub_paths(bindir libdir pkgdatadir) will create the defines PATH_BINDIR PATH_LIBDIR PATH_PKGDATADIR - see posix’ include/paths.h that creates _PATH_DEV and friends.

Source Code

Download the latest version of ax_define_sub_path.m4 or browse the macro’s revision history.


Copyright © 2008 Guido U. Draheim

Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved. This file is offered as-is, without any warranty.

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