#! /usr/bin/env ruby
#
# sample - Pick random N lines from a file.
#

num = 10
if !ARGV.empty? && ARGV[0] =~ /^-(\d+)/
  num = $1.to_i
  ARGV.shift;
end

selected = []
lineno = 1
while line = gets
  rand = rand(lineno)
  if rand < num
    selected.push(line)
    if selected.length > num
      selected.delete_at(rand)
    end
  end
  lineno += 1
end

puts selected