Find duplicate files between two directories and use hardlink to keep only one copy.

link-duplicates.rb

#!/usr/bin/env ruby

# Find duplicate files in specified directories and files and use
# hardlink to keep only one copy.

require 'digest'

if ARGV.length < 1
  name = `basename #{__FILE__}`
  puts "Usage: #{name.chomp} <path1> [path2 ...]"
  puts "    path can be either file or directory"
  exit 1
end

md5path = {}

IO.popen("find #{ARGV.join(' ')} -type f").each_line do |path|
  path = path.chomp
  md5sum = Digest::MD5.file(path).hexdigest
  duplicate_path = md5path[md5sum]
  if duplicate_path.nil?
    md5path[md5sum] = path
  else
    cmd = "ln -f #{duplicate_path} #{path}"
    puts cmd
    system cmd
  end
end