Print out unique lines in a file

uniq.rb

previous = nil
output_buffer = File.open(ARGV[1], 'w')
File.open(ARGV[0], 'r') do |f|
  prevline = nil
  curline = f.gets
  nextline = f.gets
  while !curline.nil?
    if curline != prevline && curline != nextline
      output_buffer.write(curline)
    end
    prevline = curline
    curline = nextline
    nextline = f.gets
  end
end