-void fn_interp_vars (struct substring src,
- void (*insert_variable) (const char *var,
- struct string *dst, void *aux),
- void *aux, struct string *dst);
-char *fn_search_path (const char *base_name, const char *path);
-char *fn_dir_name (const char *fn);
-char *fn_extension (const char *fn);