diff --git a/mitmproxy/optmanager.py b/mitmproxy/optmanager.py
index e1d74b8e0..830821532 100644
--- a/mitmproxy/optmanager.py
+++ b/mitmproxy/optmanager.py
@@ -512,13 +512,15 @@ def serialize(opts, text, defaults=False):
     return ruamel.yaml.round_trip_dump(data)
 
 
-def save(opts, path, defaults=False):
+def save(opts, path=None, defaults=False):
     """
-        Save to path. If the destination file exists, modify it in-place.
+        If the path is given, save to path, otherwise return the serialized data.
+
+        If the destination file exists, modify it in-place.
 
         Raises OptionsError if the existing data is corrupt.
     """
-    if os.path.exists(path) and os.path.isfile(path):
+    if path and os.path.exists(path) and os.path.isfile(path):
         with open(path, "rt", encoding="utf8") as f:
             try:
                 data = f.read()
@@ -529,5 +531,9 @@ def save(opts, path, defaults=False):
     else:
         data = ""
     data = serialize(opts, data, defaults)
-    with open(path, "wt", encoding="utf8") as f:
-        f.write(data)
+
+    if path:
+        with open(path, "wt", encoding="utf8") as f:
+            f.write(data)
+    else:
+        return data