pather code.

pather

#!/usr/bin/env ruby

class Pather
  def initialize(input)
    @input = input.split("\n")
  end

  def output
    x1 = nil
    @input.each do |line|
      unless x1
        x1 = (line =~ /#/)  
      else
        line[x1] = '*'  if x1

        # seek bottom point
        if x2 = (line =~ /#/)
          if x1 < x2
            first, second = x1, x2 - 1
          else
            first, second = x2 + 1, x1 
          end

          line[first..second] = '*' * (second - first + 1).abs
          break 
        end
      end
    end
    @input
  end
end

p "Must provide input file" if ARGV.empty?
input_file = ARGV[0]
output_file = ARGV[1] || 'output.txt'

input = File.open(File.join(File.dirname(__FILE__), input_file)).read
pather = Pather.new(input)

File.open(File.join(File.dirname(__FILE__), output_file), 'w') {|f| f.puts pather.output.join("\n") }