From: Dan Zwell <dzwell@...>
Date: 2007-07-22T15:20:17+09:00
Subject: Re: IO.popen - continuous output

Dan Zwell wrote:
> Sebastian Hungerecker wrote:
>> That *is* what you get with IO.popen.
>> For example,
>> IO.popen('tail -f testfile').each_line do |line|
>>   puts line.upcase
>> end
>> prints out the upcased version of any line added to testfile as soon 
>> as it is
>> added to the file.
>>
>>
> 
> I was just wondering about this, and I see that you are correct, 
> *usually*--this is very strange.
> 
> file1:
> #!/usr/bin/env ruby
> 5.times {puts "hi"; sleep 0.5}
> 
> file2:
> #!/usr/bin/env ruby
> IO.popen("./file1").each_line { |line| puts line }
> 
> When running file2 (which should stream the output from file1), the 
> output is not streamed, but instead saved up until "file1" finishes 
> running and then dumped. Note that this only occurs when file1 is a ruby 
> file--replacing it with a bash script that does the same thing causes 
> the output to stream properly. I am perplexed. Any insight? (Is this a 
> bug?)
> 
> I'm using ruby 1.8.5 on linux.
> 
> Dan
> 
I've made this a bit more accessible for the non-linux folks:
In IRB, try running thes one-liner (with wide margins):
IO.popen("ruby -e '5.times {|n| puts n; sleep 1}'").each_line {|line| 
puts line}

It should print a number every second, right? Well, it doesn't for me...

Dan