first stab at save-file command

currently supports:
* -i, -m, -c, -f, -l (specify lines to restrict to)

TODO:
* -a (append to file flag)
* --insert (insert at a certain point in a file)
* --indent (ensure inserted code is indented properly, using pry's indent mechanism)

lib/pry/default_commands/shell.rb

@@ -30,6 +30,73 @@ class Pry
       end
       alias_command "file-mode", "shell-mode"
 
+      command_class "save-file", "Export to a file using content from the REPL."  do
+        attr_accessor :content
+        attr_accessor :file_name
+
+        def setup
+          self.content = ""
+        end
+
+        def options(opt)
+          opt.banner unindent <<-USAGE
+  Usage: save-file [OPTIONS] [METH]
+  Save REPL content to a file.
+  e.g: save-file -m my_method -m my_method2 ./hello.rb
+  e.g: save-file -i 1..10 ./hello.rb
+  e.g: save-file -c show-method ./my_command.rb
+  e.g: save-file -f sample_file --lines 2..10 ./output_file.rb
+USAGE
+
+          opt.on :m, :method, "Save a method's source.", true do |meth_name|
+            meth = get_method_or_raise(meth_name, target, {})
+            self.content << meth.source
+          end
+          opt.on :c, :command, "Save a command's source.", true do |command_name|
+            command = find_command(command_name)
+            self.content << command.block.source
+          end
+          opt.on :f, :file, "Save a file.", true do |file|
+            self.content << File.read(File.expand_path(file))
+          end
+          opt.on :l, :lines, "Only gist a subset of lines (only works with -m and -f)", :optional => true, :as => Range, :default => 1..-1
+          opt.on :i, :in, "Gist entries from Pry's input expression history. Takes an index or range.", :optional => true,
+          :as => Range, :default => -5..-1 do |range|
+            input_expressions = _pry_.input_array[range] || []
+            Array(input_expressions).each { |v| self.content << v }
+          end
+        end
+
+        def process
+          if args.empty?
+            raise CommandError, "Must specify a file name."
+          end
+
+          self.file_name = File.expand_path(args.first)
+
+          save_file
+        end
+
+        def save_file
+          if self.content.empty?
+            raise CommandError, "Found no code to save."
+          end
+
+          File.open(file_name, "w") do |f|
+            if opts.present?(:lines)
+              f.puts restrict_to_lines(content, opts[:l])
+            else
+              f.puts content
+            end
+          end
+        end
+
+        def restrict_to_lines(content, lines)
+          line_range = one_index_range(lines)
+          content.lines.to_a[line_range].join
+        end
+      end
+
       create_command "cat", "Show code from a file, Pry's input buffer, or the last exception." do
         banner <<-USAGE
           Usage: cat FILE