diff --git a/scripts/build.py b/scripts/build.py
index 3d5d51c7..c169a68c 100644
--- a/scripts/build.py
+++ b/scripts/build.py
@@ -35,14 +35,15 @@ def read_deps(cur, prereq_type):
             return dep_cache[prereq_type][cur]
     else:
         dep_cache[prereq_type] = {}
-    p = subprocess.Popen(projects_py + " prereq " + prereq_type + " " + cur, shell=True, stdout=subprocess.PIPE)
+    cmd = projects_py + " prereq " + prereq_type + " " + cur
+    p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE)
     p.wait()
     if p.returncode:
         raise Exception("failed to get " + prereq_type + " prerequisites from " + path)
     r = Set()
     pattern = re.compile(r'.*') # might be useful at a later point, currently pointless
     for line in iter(p.stdout.readline,''):
-        debug('evaluating line:', line)
+        debug(cmd + ' returned: ', line)
         if not pattern.match(line):
             continue
         for d in line.split():
@@ -53,20 +54,26 @@ def read_deps(cur, prereq_type):
     dep_cache[prereq_type][cur] = r
     return r
 
-def add_tree(cur, prereq_type):
+def add_tree(cur, prereq_types):
+    debug("adding prerequisites " + ' '.join(prereq_types) + " of module " + cur)
     if cur in all_deps:
+        debug('already handled module ' + cur)
         return 0
+
+    deps = Set()
     all_deps.add(cur)
-    deps = read_deps(cur, prereq_type)
+    for t in prereq_types:
+        debug("checking prereqisites of type " + t)
+        deps.update(read_deps(cur, t))
     for d in deps:
-        add_tree(d, prereq_type)
+        add_tree(d, prereq_types)
     dep_tree[cur] = deps
     return len(deps)
 
 def calculate_order(order, modules, prereq_types):
-    for t in prereq_types:
-        for m in modules:
-            add_tree(m, t)
+    for m in modules:
+        debug("--- adding dependency tree of module " + m)
+        add_tree(m, prereq_types)
     while len(all_deps):
         for d in all_deps:
             if not len(dep_tree[d]):
@@ -118,6 +125,7 @@ def build(modules, order, target):
 # ------------ here we go
 
 all_deps = Set()
+visited = {}
 dep_tree = {}
 glob_order = []
 proj_base=pwd.getpwuid(os.getuid()).pw_dir + "/local/src/jw.dev/proj"
@@ -126,11 +134,13 @@ dep_cache = {}
 my_dir=os.path.dirname(os.path.realpath(__file__))
 
 # -- parse command line
-parser = argparse.ArgumentParser(description='jannet software project build tool')
+parser = argparse.ArgumentParser(description='janware software project build tool')
 parser.add_argument('--base', '-b', nargs='?', default=proj_base, help='Project base directory')
 parser.add_argument('--exclude', default='', help='Space seperated ist of modules to be excluded from build')
 parser.add_argument('--debug', '-d', action='store_true',
     default=False, help='Output debug information to stderr')
+parser.add_argument('--dry-run', '-n', action='store_true',
+    default=False, help='Don\'t build anything, just print what would be done.')
 parser.add_argument('--ignore-deps', '-I', action='store_true',
     default=False, help='Don\'t build dependencies, i.e. build only modules specified on the command line')
 parser.add_argument('target', default='all', help='Build target')
@@ -158,7 +168,7 @@ order = []
 
 glob_prereq_types = [ "build" ]
 if target == 'pkg-rebuild-reinstall':
-    glob_prereq_types == [ "build", "run", "release" ]
+    glob_prereq_types = [ "build", "run", "release", "devel" ]
 
 calculate_order(order, modules, glob_prereq_types)
 if args.ignore_deps:
@@ -175,6 +185,9 @@ for m in order:
     print("  %3d %s" % (cur_project, m))
 cur_project=0
 
+if args.dry_run:
+    exit(0)
+
 build(modules, order, target)
 
 print(datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S"))