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(C) 2007 guidod
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AC_DEFINE_SUB_PATH(DEFNAME, varname, description)



Guido U. Draheim <>


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Category ac-archive's Miscellaneous (released)


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 can not 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 (

  AC_DEFINE_DIR([EPREFIX], [exec_prefix], [--exec-prefix or default])
  AC_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 AC_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. ac_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.

M4 Source Code
  test "_$prefix" = _NONE &amp;&amp; prefix="$ac_default_prefix"
  test "_$exec_prefix" = _NONE &amp;&amp; exec_prefix='${prefix}'
  P=`echo ifelse( $2, , [$]$1, [$]$2) | sed -e 's:^\${[a-z_]*prefix}:.:'`
  ifelse ($3, ,
    AC_DEFINE($1, $P, [sub path $2]),
    AC_DEFINE($1, $P, $3))

  test "_$prefix" = _NONE &amp;&amp; prefix="$ac_default_prefix"
  test "_$exec_prefix" = _NONE &amp;&amp; exec_prefix='${prefix}'
  for i in $1 ; do
  P=`echo \$$i | sed -e 's:^\${[a-z_]*prefix}:.:'`
  V=`echo path_$i | sed -e 'y:abcdefghijklmnopqrstuvwxyz:ABCDEFGHIJKLMNOPQRSTUVWXYZ:'`
    AC_DEFINE($V, $P, [sub path $i]),