This piece of code will report the chunk of code that caused exception

pretty_exceptions.rb

class StandardError

  alias :original_backtrace :backtrace

  def backtrace
    unless original_backtrace.nil?
      file, number = original_backtrace.first.split(':')
      $stdout.print "\n# %s\n\n" % file
      __get_script_line(file, number.to_i) do |line|
        $stdout.print line
      end
      $stdout.print "\n"
    end
    original_backtrace
  end

  private

  def __get_script_line(file, line)
    __SCRIPT_LINES = open(file) { |f| f.readlines }
    3.downto(-1) do |i|
      yield __print_line(line-i, __SCRIPT_LINES[line-i], (i==1))
    end
  end

  def __print_line(number, line, color=false)
    if color
      sprintf("\033[1;37m>%i: %s\033[0m", number, line)
    else
      sprintf(" %i: %s", number, line)
    end
  end

end

#
#
#  def test1
#    b += 1
#  end
#
#  $ ruby test.rb 
#
#  test.rb
#
#  37: def test1
# >38:   b += 1
#  39: end
#  40:
#
# test.rb:38:in `test1': undefined method `+' for nil:NilClass (NoMethodError)
#	from test.rb:37