Port dedent from Python

CHANGELOG

@@ -9,6 +9,7 @@
 * cat --ex now works on exceptions in REPL-defined code
 * play -m now uses eval_string.replace()
 * play -m --open uses show-input to show play'd code
+* added "unindent" helper to make adding help to commands easier
 
 8/9/2011 version 0.9.5
 

lib/pry/helpers/command_helpers.rb

@@ -443,6 +443,47 @@ def prompt(message, options="Yn")
         end
       end
 
+      # Remove any common leading whitespace from every line in `text`.
+      #
+      # This can be used to make a HEREDOC line up with the left margin, without
+      # sacrificing the indentation level of the source code.
+      #
+      # e.g.
+      #   opt.banner unindent <<-USAGE
+      #     Lorem ipsum dolor sit amet, consectetur adipisicing elit,
+      #     sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
+      #       "Ut enim ad minim veniam."
+      #   USAGE
+      #
+      # @param  [String] The text from which to remove indentation
+      # @return [String], The text with indentation stripped.
+      #
+      # @copyright Heavily based on textwrap.dedent from Python, which is:
+      #   Copyright (C) 1999-2001 Gregory P. Ward.
+      #   Copyright (C) 2002, 2003 Python Software Foundation.
+      #   Written by Greg Ward <gward@python.net>
+      #
+      #   Licensed under <http://docs.python.org/license.html>
+      #   From <http://hg.python.org/cpython/file/6b9f0a6efaeb/Lib/textwrap.py>
+      #
+      def unindent(text)
+        # Empty blank lines
+        text = text.sub(/^[ \t]+$/, '')
+
+        # Find the longest common whitespace to all indented lines
+        margin = text.scan(/^[ \t]*(?=[^ \t\n])/).inject do |current_margin, next_indent|
+          if next_indent.start_with?(current_margin)
+            current_margin
+          elsif current_margin.start_with?(next_indent)
+            next_indent
+          else
+            ""
+          end
+        end
+
+        text.gsub(/^#{margin}/, '')
+      end
+
     end
 
   end