使用Ruby简单实现的tail命令，支持动态输出

1 #!/usr/bin/ruby
 2 
 3 line = ARGV[0]
 4 filename = ARGV[1]
 5 
 6 unless line && filename then
 7     print "Invalid parameter.\n"
 8     print "Usage:ruby tail.rb line filename\n"
 9 end
10 line = line.to_i
11 
12 begin
13     io = open(filename)
14     n = 0
15     lc = 0
16     stack = Array.new
17 
18     while lc < line + 1 do
19         n = n + 1
20         io.seek( -n, IO::SEEK_END )
21         if io.pos == 0 then
22             break
23         end
24         #break unless io.seek( -n ,IO::SEEK_END)
25         s = io.read( 1 )
26         if /\n/ =~ s then
27             lc = lc + 1
28         end
29     end
30 
31     io.seek(-n, IO::SEEK_END)
32     s = io.read()
33     last = io.pos
34     print s
35 
36     while item = io.read() do
37         if ! item.empty? then
38             print item
39             last = io.pos
40         else
41             io.pos = last
42         end
43     end
44 rescue
45     print $@, "\n"
46 end