Rewrite 'edit-command'.

You no longer need to provide a variable that references a CommandSet…
Instead, you can provide just the command name.

The only cavaet is that the file defining the command you're editing
must return the CommandSet it is being written within.

You can also rewrite commands temporarily (in-memory) with the -p
switch.

lib/pry/extended_commands/user_command_api.rb

@@ -39,25 +39,74 @@ class Pry
         set_file_and_dir_locals(file_name)
       end
 
-      command "edit-command", "Edit a command. edit-command CMD_NAME CMD_SET" do |command_name, set_name|
-        if command_name.nil?
-          raise CommandError, "Must provide command name"
+      command_class "edit-command", "Edit a Pry command." do
+        banner <<-BANNER
+          Usage: edit-command [options] command
+          Edit a Pry command.
+        BANNER
+
+        def initialize env
+          @pry = env[:pry_instance]
+          @command = nil
         end
 
-        if set_name.nil?
-          raise CommandError, "Must provide command set name"
+        def options(opt)
+          opt.on :p, :patch, 'Perform a in-memory edit of a command'
         end
 
-        cmd = Pry.config.commands.commands[command_name]
-        file_name = cmd.block.source_location.first
+        def process
+          @command = @pry.commands.find_command(args.first)
 
-        invoke_editor(*cmd.block.source_location)
-        silence_warnings do
-          load file_name
+          if @command.nil?
+            raise Pry::CommandError, 'Command not found.'
+          end
+
+          case
+          when opts.present?(:patch)
+            edit_temporarily
+          else
+            edit_permanently
+          end
+        end
+
+        def edit_permanently
+          file, lineno = @command.block.source_location
+          invoke_editor(file, lineno)
+
+          command_set = silence_warnings do
+            eval File.read(file), TOPLEVEL_BINDING, file, 1
+          end
+
+          unless command_set.is_a?(Pry::CommandSet)
+            raise Pry::CommandError,
+                  "Expected file '#{file}' to return a CommandSet"
+          end
+
+          @pry.commands.delete(@command.name)
+          @pry.commands.import(command_set)
+          set_file_and_dir_locals(file)
+        end
+
+        def edit_temporarily
+          source_code = @command.block.source
+
+          temp_file :unlink => false do |f|
+            f.write(source_code)
+            f.flush
+
+            invoke_editor(f.path, 1)
+            modified_code = File.read(f.path)
+
+            command_set = CommandSet.new do
+              silence_warnings do
+                eval(modified_code, binding, f.path, 1)
+              end
+            end
+
+            @pry.commands.delete(@command.name)
+            @pry.commands.import(command_set)
+          end
         end
-        Pry.config.commands.import target.eval(set_name)
-        _pry_.commands.import target.eval(set_name)
-        set_file_and_dir_locals(file_name)
       end
 
     end

lib/pry/helpers/command_helpers.rb

@@ -21,11 +21,11 @@ class Pry
 
       # Open a temp file and yield it to the block, closing it after
       # @return [String] The path of the temp file
-      def temp_file
+      def temp_file opts = { :unlink => true }
         file = Tempfile.new(['pry', '.rb'])
         yield file
       ensure
-        file.close(true)
+        file.close(opts[:unlink])
       end
 
       def get_method_or_raise(name, target, opts={}, omit_help=false)