Add utility methods.

pipeCommand allows to simulate shell pipes.

failIfPathExists allows to stop in case of path which exists.

slapos/recipe/build.py

@@ -172,6 +172,32 @@ class Script:
     self.cleanup_dir_list.append(extract_dir)
     return extract_dir
 
+  def pipeCommand(self, command_list_list, *args, **kwargs):
+    """Allows to do shell like pipes (|)"""
+    subprocess_list = []
+    previous = None
+    kwargs['stdout'] = subprocess.PIPE
+    run_list = []
+    for command_list in command_list_list:
+      if previous is not None:
+        kwargs['stdin'] = previous.stdout
+      p = subprocess.Popen(command_list, *args, **kwargs)
+      if previous is not None:
+        previous.stdout.close()
+      subprocess_list.append((p, command_list))
+      run_list.append(' '.join(command_list))
+      previous = p
+    self.logger.info('Running: %r' % ' | '.join(run_list))
+    subprocess_list.reverse()
+    [q[0].wait() for q in subprocess_list]
+    for q in subprocess_list:
+      if q[0].returncode != 0:
+        raise zc.buildout.UserError('Failed while running command %r' % q[1])
+
+  def failIfPathExists(self, path):
+    if os.path.lexists(path):
+      raise zc.buildout.UserError('Path %r exists, cannot continue' % path)
+
   def copyTree(self, origin, destination, ignore_dir_list=None):
     """Recursively Copy directory.