Run S3 configuration file through ERB before parsing the YAML.

lib/paperclip.rb

@@ -25,6 +25,7 @@
 #
 # See the +has_attached_file+ documentation for more details.
 
+require 'erb'
 require 'tempfile'
 require 'paperclip/upfile'
 require 'paperclip/iostream'

lib/paperclip/storage.rb

@@ -227,9 +227,9 @@ module Paperclip
       def find_credentials creds
         case creds
         when File
-          YAML.load_file(creds.path)
+          YAML::load(ERB.new(File.read(creds.path)).result)
         when String
-          YAML.load_file(creds)
+          YAML::load(ERB.new(File.read(creds)).result)
         when Hash
           creds
         else

test/fixtures/s3.yml

@@ -2,3 +2,7 @@ development:
   key: 54321
 production:
   key: 12345
+test:
+  bucket: <%= ENV['S3_BUCKET'] %>
+  access_key_id: <%= ENV['S3_KEY'] %>
+  secret_access_key: <%= ENV['S3_SECRET'] %>

test/storage_test.rb

@@ -236,6 +236,29 @@ class StorageTest < Test::Unit::TestCase
     end
   end
 
+  context "with S3 credentials in a YAML file" do
+    setup do
+      ENV['S3_KEY']    = 'env_key'
+      ENV['S3_BUCKET'] = 'env_bucket'
+      ENV['S3_SECRET'] = 'env_secret'
+
+      rails_env('test')
+
+      rebuild_model :storage        => :s3,
+                    :s3_credentials => File.new(File.join(File.dirname(__FILE__), "fixtures/s3.yml"))
+
+      Dummy.delete_all
+
+      @dummy = Dummy.new
+    end
+
+    should "run it the file through ERB" do
+      assert_equal 'env_bucket', @dummy.avatar.bucket_name
+      assert_equal 'env_key', AWS::S3::Base.connection.options[:access_key_id]
+      assert_equal 'env_secret', AWS::S3::Base.connection.options[:secret_access_key]
+    end
+  end
+
   unless ENV["S3_TEST_BUCKET"].blank?
     context "Using S3 for real, an attachment with S3 storage" do
       setup do