From: Robert Klemme <shortcutter@...>
Date: 2007-02-22T19:20:09+09:00
Subject: Re: ruby tail

On 22.02.2007 10:59, Alex Young wrote:
> Kevin Jackson wrote:
>>> Actually, I am not sure how this would work.  If I do this, I get no 
>>> output from the file:
>>>
>>> `tail -f sim.out`
>>>
>>> So there is something basic I am missing here.  Any help?
>>
>> it shells out to the process and waits for it to return - with -f does
>> tail ever return? if not you may not be able to use it - AFAIK ` and
>> exec are the same - someone with better ruby knowledge may be able to
>> offer a solution - perhaps using threads or something
> Use IO.popen:
> 
> IO.popen('tail -f sim.out'){|f|
>     while line = f.gets
>         p line
>     end
> }

You can do it in pure Ruby:

11:14:14 [Temp]: rm x; for ((i=0;i<30;++i)); do echo $i; sleep 0.2; done 
 > x & ruby tail.rb
removed `x'
[1] 2252
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
[1]+  Done                    for ((i=0; i<30; ++i))
do
     echo $i; sleep 0.2;
done > x
tail.rb:12:in `sleep': Interrupt
         from tail.rb:12:in `tail'
         from tail.rb:5:in `loop'
         from tail.rb:5:in `tail'
         from tail.rb:16
11:14:31 [Temp]: cat tail.rb
# we never return!
def tail(file)
   io = File.open(file)

   loop do
     while ( line = io.gets )
       puts line
     end

     # uncomment next to watch what is happening
     # puts "-"
     sleep 1
   end
end

tail "x"
11:14:35 [Temp]:

Kind regards

	robert