local args = {...} --get the arguments from the command line and put them in the table named args

if #args < 1 then --if we did not get any arguments, tell the user to provide them
  print("Usage: "..fs.getName(shell.getRunningProgram()).." <length>") --fancy stuff to print the name of the program.
  return --quit early, since we got no arguments.
elseif tonumber(args[1]) == nil then --the user gave us an argument, but it was not a number! Print usage again.
  print("Usage: "..fs.getName(shell.getRunningProgram()).." <length>")
  return
end

--now, since the code made it here, we must have at least one argument that can be made into a number.

local length = tonumber(args[1]) --take the first argument (that is the [1] part, the first index of the table), convert it to a number, and store the result in our length variable.