#! /usr/local/bin/ruby
# /home/tetsu/src/ruby/toolbox/tail.rb
# Created: August 17,2000 Thursday 19:59:29
# Author: tetsu(WATANABE Tetsuya)
# $Id: tail.rb,v 1.5 2001/03/12 13:51:03 tetsu Exp $

def tail(f, opt_line, arr)
  begin
    f.seek(-32 * 1024, IO::SEEK_END)
  rescue Errno::EINVAL, Errno::ESPIPE
  end
  count = 0

  while f.gets
    arr[count % opt_line] = $_
    count += 1
  end

  if count > opt_line
    n = opt_line
  else
    n = count
    count = 0
  end

  n.times do |i|
    print arr[(i + count) % opt_line]
  end
end

def tailf(f)
  while true
    begin
      sleep 1
      $_ = f.sysread(1024)
      print
    rescue EOFError
    end
  end
end

def skip(f, skip_lines)
  1.upto(skip_lines) do
    break if f.gets.nil?
  end
  while f.gets
    print
  end
end

def usage
  STDERR.print "usage: #$0 [-f] [-Lines|+SkipLines] [file...]\n"
  exit 1
end

opt_lines = 10
opt_skip_lines = 0
opt_follow = false

while ARGV[0] =~ /^(?:-|\+)/
  case ARGV.shift
  when /^-(\d+)/
    opt_lines = $1.to_i
  when /^\+(\d+)/
    opt_skip_lines = $1.to_i
  when /^-f/
    opt_follow = true
  else
    usage
  end
end

arr = Array.new(opt_lines)

case ARGV.size
when 0
  if opt_skip_lines > 0
    skip(STDIN, opt_skip_lines)
  else
    tail(STDIN, opt_lines, arr)
  end
when 1
else
  opt_filename = true
end

while filename = ARGV.shift
  f = File.open(filename)
  print '==> ', filename, " <==\n" if opt_filename
  if opt_skip_lines > 0
    skip(f, opt_skip_lines)
  else
    tail(f, opt_lines, arr)
  end
  tailf(f) if opt_follow
  f.close
end