Index: bin/stamp2json
===================================================================
--- bin/stamp2json	(revision 16)
+++ bin/stamp2json	(revision 17)
@@ -2,6 +2,7 @@
 
 import json
+import sys
 from argparse import ArgumentParser
-from os.path import expanduser
+from os.path import expanduser, isfile, isdir
 
 
@@ -59,4 +60,20 @@
                 'action': action,
             })
+
+    if isfile(args.output):
+        print('[warning] %(out)s already exist'
+              % {'out': args.output})
+        confirm = raw_input('overwrite? (y/n) ')
+        while confirm not in ['y','n','Y','N']:
+            confirm = raw_input('overwrite? (y/n) ')
+        if confirm in ['n', 'N']:
+            print('[warning] exiting without converting')
+            sys.exit()
+
+    elif isdir(args.output):
+        print('[error] %(out)s is a directory, remove it first'
+              % {'out': args.output})
+        sys.exit(1)
+
     with open(args.output, 'w') as stamps_file:
         json.dump(stamps, stamps_file, indent=4)