Added a CommandLine class to handle all the running and the whatnot.

lib/paperclip.rb

@@ -38,6 +38,7 @@ require 'paperclip/interpolations'
 require 'paperclip/style'
 require 'paperclip/attachment'
 require 'paperclip/callback_compatability'
+require 'paperclip/command_line'
 require 'paperclip/railtie'
 if defined?(Rails.root) && Rails.root
   Dir.glob(File.join(File.expand_path(Rails.root), "lib", "paperclip_processors", "*.rb")).each do |processor|

lib/paperclip/command_line.rb

+module Paperclip
+  class CommandLine
+    class << self
+      attr_accessor :path
+    end
+
+    def initialize(binary, params = "", options = {})
+      @binary            = binary.dup
+      @params            = params.dup
+      @options           = options.dup
+      @swallow_stderr    = @options.delete(:swallow_stderr)
+      @expected_outcodes = @options.delete(:expected_outcodes)
+      @expected_outcodes ||= [0]
+    end
+
+    def command
+      cmd = []
+      cmd << full_path(@binary)
+      cmd << interpolate(@params, @options)
+      cmd << bit_bucket if @swallow_stderr
+      cmd.join(" ")
+    end
+
+    def run
+      output = `#{command}`
+      unless @expected_outcodes.include?($?.exitstatus)
+        raise Paperclip::PaperclipCommandLineError, "Command '#{command}' returned #{$?.exitstatus}. Expected #{@expected_outcodes.join(", ")}"
+      end
+      output
+    end
+
+    private
+
+    def full_path(binary)
+      [self.class.path, binary].compact.join("/")
+    end
+
+    def interpolate(pattern, vars)
+      # interpolates :variables and :{variables}
+      pattern.gsub(%r#:(?:\w+|\{\w+\})#) do |match|
+        key = match[1..-1]
+        key = key[1..-2] if key[0,1] == '{'
+        if invalid_variables.include?(key)
+          raise PaperclipCommandLineError,
+            "Interpolation of #{key} isn't allowed."
+        end
+        shell_quote(vars[key.to_sym])
+      end
+    end
+
+    def invalid_variables
+      %w(expected_outcodes swallow_stderr)
+    end
+
+    def shell_quote(string)
+      return "" if string.nil? or string.blank?
+      string.split("'").map{|m| "'#{m}'" }.join("\\'")
+    end
+
+    def bit_bucket
+      return "2>NUL" unless File.exist?("/dev/null")
+      "2>/dev/null"
+    end
+  end
+end

test/command_line_test.rb

+require 'test/helper'
+
+class CommandLineTest < Test::Unit::TestCase
+  def setup
+    Paperclip::CommandLine.path = nil
+  end
+
+  should "take a command and parameters and produce a shell command for bash" do
+    cmd = Paperclip::CommandLine.new("convert", "a.jpg b.png")
+    assert_equal "convert a.jpg b.png", cmd.command
+  end
+
+  should "be able to set a path and produce commands with that path" do
+    Paperclip::CommandLine.path = "/opt/bin"
+    cmd = Paperclip::CommandLine.new("convert", "a.jpg b.png")
+    assert_equal "/opt/bin/convert a.jpg b.png", cmd.command
+  end
+
+  should "be able to interpolate quoted variables into the parameters" do
+    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",
+                                     :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",
+                                     "a.jpg b.png",
+                                     :swallow_stderr => true)
+
+    assert_equal "convert a.jpg b.png 2>/dev/null", cmd.command
+  end
+
+  should "add redirection to get rid of stderr in cmd.exe" do
+    File.stubs(:exist?).with("/dev/null").returns(false)
+    cmd = Paperclip::CommandLine.new("convert",
+                                     "a.jpg b.png",
+                                     :swallow_stderr => true)
+
+    assert_equal "convert a.jpg b.png 2>NUL", cmd.command
+  end
+
+  should "raise if trying to interpolate :swallow_stderr or :expected_outcodes" do
+    cmd = Paperclip::CommandLine.new("convert",
+                                     ":swallow_stderr :expected_outcodes",
+                                     :swallow_stderr => false,
+                                     :expected_outcodes => [0, 1])
+    assert_raise(Paperclip::PaperclipCommandLineError) do
+      cmd.command
+    end
+  end
+
+  should "run the #command it's given and return the output" do
+    cmd = Paperclip::CommandLine.new("convert", "a.jpg b.png")
+    cmd.stubs(:"`").with("convert a.jpg b.png").returns(:correct_value)
+    with_exitstatus_returning(0) do
+      assert_equal :correct_value, cmd.run
+    end
+  end
+
+  should "raise a PaperclipCommandLineError if the result code isn't expected" do
+    cmd = Paperclip::CommandLine.new("convert", "a.jpg b.png")
+    cmd.stubs(:"`").with("convert a.jpg b.png").returns(:correct_value)
+    with_exitstatus_returning(1) do
+      assert_raises(Paperclip::PaperclipCommandLineError) do
+        cmd.run
+      end
+    end
+  end
+
+  should "not raise a PaperclipCommandLineError if the result code is expected" do
+    cmd = Paperclip::CommandLine.new("convert",
+                                     "a.jpg b.png",
+                                     :expected_outcodes => [0, 1])
+    cmd.stubs(:"`").with("convert a.jpg b.png").returns(:correct_value)
+    with_exitstatus_returning(1) do
+      assert_nothing_raised do
+        cmd.run
+      end
+    end
+  end
+end

test/helper.rb

@@ -146,3 +146,13 @@ def should_reject_dummy_class
     assert_rejects @matcher, @dummy_class.new
   end
 end
+
+def with_exitstatus_returning(code)
+  saved_exitstatus = $?.nil? ? 0 : $?.exitstatus
+  begin
+    `ruby -e 'exit #{code.to_i}'`
+    yield
+  ensure
+    `ruby -e 'exit #{saved_exitstatus.to_i}'`
+  end
+end

test/paperclip_test.rb

@@ -87,8 +87,8 @@ class PaperclipTest < Test::Unit::TestCase
     Paperclip.options[:command_path]      = nil
     Paperclip.options[:log_command]       = false
     Paperclip.options[:swallow_stderr]    = false
-    Paperclip.expects(:"`").with(%q[this 'is' 'jack'\''s' '`command`' 'line!'])
-    Paperclip.run("this", "is", "jack's", "`command`", "line!")
+    Paperclip.expects(:"`").with(%q[this is 'jack'\''s' '`command`' 'line!'])
+    Paperclip.run("this", "is :one :two :three", :one => "jack's", :two => "`command`", :three => "line!")
   end
 
   context "Paperclip.bit_bucket" do