Also give a CommandNotFoundError if backtick raises Errno::ENOENT.

lib/paperclip.rb

@@ -112,16 +112,20 @@ module Paperclip
       command = "#{command} 2>#{bit_bucket}" if Paperclip.options[:swallow_stderr]
       Paperclip.log(command) if Paperclip.options[:log_command]
 
+      begin
         output = `#{command}`
 
-      if $?.exitstatus == 127
-        raise CommandNotFoundError
-      end
+        raise CommandNotFoundError if $?.exitstatus == 127
+
         unless expected_outcodes.include?($?.exitstatus)
           raise PaperclipCommandLineError,
             "Error while running #{cmd}. Expected return code to be #{expected_outcodes.join(", ")} but was #{$?.exitstatus}",
             output
         end
+      rescue Errno::ENOENT => e
+        raise CommandNotFoundError
+      end
+
       output
     end
 

test/paperclip_test.rb

@@ -63,7 +63,7 @@ class PaperclipTest < Test::Unit::TestCase
   end
 
   context "Calling Paperclip.run when the command is not found" do
-    should "tell you the command isn't there" do
+    should "tell you the command isn't there if the shell returns 127" do
       begin
         assert_raises(Paperclip::CommandNotFoundError) do
           `ruby -e 'exit 127'` # Stub $?.exitstatus to be 127, i.e. Command Not Found.
@@ -74,6 +74,12 @@ class PaperclipTest < Test::Unit::TestCase
         `ruby -e 'exit 0'` # Unstub $?.exitstatus
       end
     end
+    should "tell you the command isn't there if an ENOENT is raised" do
+      assert_raises(Paperclip::CommandNotFoundError) do
+        Paperclip.stubs(:"`").raises(Errno::ENOENT)
+        Paperclip.run("command")
+      end
+    end
   end
 
   should "prevent dangerous characters in the command via quoting" do