Simple tail implementation in lua

tail.lua

#!/usr/bin/env lua
-- Example usage: ./tail.lua logfile -10
local fd=io.open(arg[1],"r")
local lines_to_read=math.abs(tonumber(arg[2]) or 0)
local eof=fd:seek("end",-1)
local pos=eof
local lines_read=0
local buf={}
local buf_len=0
while pos do
  local byte=fd:read(1)
  if byte=="\n" then
    if pos<eof then
      lines_read=lines_read+1
    end
    if lines_read>=lines_to_read then
      break
    end
  end
  buf_len=buf_len+1
  buf[buf_len]=byte
  pos=fd:seek("cur",-2)
end
io.write(table.concat(buf):reverse())