Don't use single-quote to quote windows command lines.

lib/paperclip/command_line.rb

@@ -62,12 +62,19 @@ def invalid_variables
 
     def shell_quote(string)
       return "" if string.nil? or string.blank?
-      string.split("'").map{|m| "'#{m}'" }.join("\\'")
+      if self.class.unix?
+        string.split("'").map{|m| "'#{m}'" }.join("\\'")
+      else
+        %{"#{string}"}
+      end
     end
 
     def bit_bucket
-      return "2>NUL" unless File.exist?("/dev/null")
-      "2>/dev/null"
+      self.class.unix? ? "2>/dev/null" : "2>NUL"
+    end
+
+    def self.unix?
+      File.exist?("/dev/null")
     end
   end
 end

test/command_line_test.rb

@@ -3,6 +3,7 @@
 class CommandLineTest < Test::Unit::TestCase
   def setup
     Paperclip::CommandLine.path = nil
+    File.stubs(:exist?).with("/dev/null").returns(true)
   end
 
   should "take a command and parameters and produce a shell command for bash" do
@@ -24,6 +25,15 @@ def setup
     assert_equal "convert 'a.jpg' 'b.png'", cmd.command
   end
 
+  should "quote command line options differently if we're on windows" do
+    File.stubs(:exist?).with("/dev/null").returns(false)
+    cmd = Paperclip::CommandLine.new("convert",
+                                     ":one :{two}",
+                                     :one => "a.jpg",
+                                     :two => "b.png")
+    assert_equal 'convert "a.jpg" "b.png"', cmd.command
+  end
+
   should "be able to quote and interpolate dangerous variables" do
     cmd = Paperclip::CommandLine.new("convert",
                                      ":one :two",
@@ -32,6 +42,15 @@ def setup
     assert_equal "convert '`rm -rf`.jpg' 'ha'\\''ha.png'", cmd.command
   end
 
+  should "be able to quote and interpolate dangerous variables even on windows" do
+    File.stubs(:exist?).with("/dev/null").returns(false)
+    cmd = Paperclip::CommandLine.new("convert",
+                                     ":one :two",
+                                     :one => "`rm -rf`.jpg",
+                                     :two => "ha'ha.png")
+    assert_equal %{convert "`rm -rf`.jpg" "ha'ha.png"}, cmd.command
+  end
+
   should "add redirection to get rid of stderr in bash" do
     File.stubs(:exist?).with("/dev/null").returns(true)
     cmd = Paperclip::CommandLine.new("convert",
@@ -96,4 +115,14 @@ def setup
     Paperclip.expects(:log).with("convert a.jpg b.png")
     cmd.run
   end
+
+  should "detect that the system is unix or windows based on presence of /dev/null" do
+    File.stubs(:exist?).returns(true)
+    assert Paperclip::CommandLine.unix?
+  end
+
+  should "detect that the system is not unix or windows based on absence of /dev/null" do
+    File.stubs(:exist?).returns(false)
+    assert ! Paperclip::CommandLine.unix?
+  end
 end