diff --git a/dotdrop/action.py b/dotdrop/action.py
index 51676cd..809fd1c 100644
--- a/dotdrop/action.py
+++ b/dotdrop/action.py
@@ -5,6 +5,7 @@ Represent an action in dotdrop
 """
 
 import subprocess
+import os
 
 # local imports
 from dotdrop.logger import Logger
@@ -12,29 +13,37 @@ from dotdrop.logger import Logger
 
 class Action:
 
+
     def __init__(self, key, action):
         self.key = key
         self.action = action
         self.log = Logger()
 
     def execute(self):
+        ret = 1
         self.log.sub('executing \"%s\"' % (self.action))
         try:
-            subprocess.call(self.action, shell=True)
+            ret = subprocess.call(self.action, shell=True)
         except KeyboardInterrupt:
             self.log.warn('action interrupted')
+        return ret == 0
 
     def transform(self, arg0, arg1):
         '''execute transformation with {0} and {1}
         where {0} is the file to transform and
         {1} is the result file'''
+        if os.path.exists(arg1):
+            msg = 'transformation destination exists: %s'
+            self.log.warn(msg % (arg1))
+            return False
+        ret = 1
         cmd = self.action.format(arg0, arg1)
         self.log.sub('transforming with \"%s\"' % (cmd))
         try:
-            subprocess.call(cmd, shell=True)
+            ret = subprocess.call(cmd, shell=True)
         except KeyboardInterrupt:
             self.log.warn('action interrupted')
-        return arg1
+        return ret == 0
 
     def __str__(self):
         return 'key:%s -> \"%s\"' % (self.key, self.action)