Feature/support passing ref to user data

README.rst

@@ -255,6 +255,23 @@ Duplicating a single instance sample would look like this
 
     print(template.to_json())
 
+UserData
+========
+You can pass in user data script to your launch config using ``from_file`` helper function under helpers/userdata.py file.
+You can also use ``Ref`` method in the script file which will be translated into CloudFormation function.
+
+Example:
+
+.. code:: bash
+
+    #!/bin/bash -ex
+
+    /opt/aws/bin/cfn-init -v --stack "Ref('AWS::StackName')" \
+      --resource LaunchConfig \
+      --configsets ConfigCluster \
+      --region Ref('AWS::Region')
+
+
 Community
 =========
 

tests/test_userdata.py

@@ -56,6 +56,20 @@ def test_char_escaping(self):
     def test_nonexistant_file(self):
         self.assertRaises(IOError, self.create_result, 'nonexistant.sh')
 
+    def test_if_ref_is_replaced(self):
+        result = self.create_result('ref_func.sh')
+
+        answer = self.create_answer([
+            '/opt/aws/bin/cfn-init -v --stack "',
+            {'Ref': 'AWS::StackName'},
+            '" \\\n',
+            '  --resource LaunchConfig \\\n',
+            '  --configsets ConfigCluster \\\n',
+            '  --region ',
+            {'Ref': 'AWS::Region'},
+            '\n'])
+        self.assertEqual(result, answer)
+
 
 if __name__ == '__main__':
     unittest.main()

tests/userdata_test_scripts/ref_func.sh

@@ -0,0 +1,4 @@
+/opt/aws/bin/cfn-init -v --stack "Ref('AWS::StackName')" \
+  --resource LaunchConfig \
+  --configsets ConfigCluster \
+  --region Ref('AWS::Region')

troposphere/helpers/userdata.py

@@ -1,11 +1,14 @@
 #!/usr/bin/python
 
-from troposphere import Base64, Join
+import re
 
+from troposphere import Base64, Join, Ref
 
-def from_file(filepath, delimiter='', blanklines=False):
+
+def from_file(filepath, delimiter='', blanklines=False, searchref=True):
     """
     Imports userdata from a file.
+    Also supports passing Troposphere Ref function
 
     :type filepath: string
     :param filepath
@@ -31,6 +34,22 @@ def from_file(filepath, delimiter='', blanklines=False):
                 if blanklines and line.strip('\n\r ') == '':
                     continue
 
+                if searchref:
+                    pattern = r"""(?P<prefix>.*)
+                    Ref\(\'(?P<reference>[a-zA-Z0-9\:]+)\'\)
+                    (?P<suffix>.*[^\\*])"""
+                    ref_pattern = re.compile(pattern, re.VERBOSE)
+
+                    ref_ex = ref_pattern.match(line)
+
+                    if ref_ex:
+                        data.append(ref_ex.group('prefix'))
+                        data.append(Ref(ref_ex.group('reference')))
+
+                        if ref_ex.group('suffix'):
+                            data.append(ref_ex.group('suffix'))
+                            continue
+
                 data.append(line)
     except IOError:
         raise IOError('Error opening or reading file: {}'.format(filepath))