From: Paul Brannan <pbrannan@...>
Date: 2002-07-30T22:35:03+09:00
Subject: Re: A very basic tail -f implementation

On Tue, Jul 30, 2002 at 05:15:25AM +0900, Daniel Berger wrote:
> # Ctrl-C to exit
> while true
>    puts t.read
> end

I have an implementation of tail -f that looks similar, except it
doesn't seek to the end of file at start, and it's called like this:

  File.open(filename) do |input|
    tail_f(input) do |line|
      puts line
    end
  end

Two advantages here:
  1) If an exception is raised from inside the block, the file will be
     properly closed.
  2) I get my input line-by-line, which imo is much more useful than
     buffersize-by-buffersize.

Some advantages of your implementation:
  1) It is an object, and acts somewhat like an IO object, thus
  2) If RCR#65 (http://www.rubygarden.org/article.php?sid=179) were
     accepted, it could easily be modified to inherit from IO and make
     this class act just like a pipe.
  3) The sleep interval and buffer size are adjustable.

My implementation:

  def clearerr(io)
    offset = io.tell
    io.seek(offset)
  end

  def tail_f(input)
    loop do
      line = input.gets
      yield line if not line.nil?
      if input.eof? then
        sleep 1
        clearerr(input)
      end
    end
  end

Paul