hee.rb

#!/usr/bin/env ruby
# encoding: utf-8
# usage:
# $ command arg1 arg2 arg3 | hee
require 'pathname'

$kcode = 'u'
$stdout.sync = true

# # .zshrc
# setopt inc_append_history
histfile = ENV['HISTFILE']

def read_last_line(filename)
  open(filename) do |file|
    bufsize = 1024
    pos = 0
    separator_found = false
    result = ''
    file.seek(0, IO::SEEK_END)

    until separator_found
      file.seek(bufsize > file.pos ? - file.pos : - bufsize, IO::SEEK_CUR)
      pos = file.pos
      buf = file.read(bufsize)

      # end of file
      if buf.match(/#{$/}\z/) && result == ''
        buf = buf.slice(0, buf.size - $/.size)
      end

      match = buf.match(/#{$/}+([^#{$/}]*)\z/m)
      if match
        result = match[1] + result
        separator_found = true
      else
        result = buf + result
        file.seek(pos)
      end
    end

    result
  end
end

last_cmd = read_last_line(Pathname(histfile).expand_path)

$stdout.puts '# %s $ %s' % [Dir.pwd, last_cmd]
while buf = $stdin.read(1024)
  $stdout.write(buf)
end