From: Paul Winward <pwinward@...>
Date: 2008-05-11T04:28:26+09:00
Subject: Re: capture output in real time

I found a perl solution at http://www.perlmonks.org/?node_id=305812 that 
makes use of pseudo tty to get line-buffered output.  Unfortunately, I 
can find very little documentation on how to use the ruby module PTY, 
and it looks like it is no longer supported 
(http://www.ruby-forum.com/topic/134771#new).  Also, I wonder if a 
pseudo tty can capture stderr as well 
(http://unix.derkeiler.com/Newsgroups/comp.unix.programmer/2003-07/0544.html)

The perl solution is system dependent, but it worked for me on Linux 
2.6.22.  I did see a debian package  libpty-ruby but I don't see any 
documentation and am not sure if this is still supported.

The notion of a pseudo tty is new to me and I'd appreciate any help.  Is 
there a ruby equivalent for the perl solution below?

Thanks

#!/usr/bin/perl -w
use strict;
use IO::Pty;

my $pty = new IO::Pty;
my $slave = $pty->slave();

my $pid = fork();
die "Couldn't fork: $!" unless defined $pid;

if($pid){  # dup STDOUT to Pty and run external program:
    $pty->close_slave();
    open(STDOUT, ">&",$pty)||die $!;
    system "perl blackbox.pl";
    print "\cD"; # send ^d to end

} else {    # this is your monitoring process
    $pty->make_slave_controlling_terminal();
    print "*$_" while <$slave>;
    exit;
}
__END__




Paul Winward wrote:
> Another approach I had tried was to use IO.select, as shown in
> http://whynotwiki.com/Ruby_/_Process_management ( attributed to Jamis 
> Buck).  This too, produced the same delay in output, but is shown below:
> 
> Thank you for any help
> 
> def read_until(pipe, stop_at, verbose = true)
>   lines = []
>   line = ""
>   while result = IO.select([pipe])  #, nil, nil, 10)
>     next if result.empty?
> 
>     c = pipe.read(1)
>     break if c.nil?
> 
>     line << c
>     break if line =~ stop_at
> 
>     # Start a new line?
>     if line[-1] == ?\n
>       puts line if verbose
>       lines << line
>       line = ""
>     end
>   end
>   lines
> end
> 
> 
> 
> Paul Winward wrote:
>> Thanks for the suggestion but I'm still having the problem.
>> 
>> Paul
>> 
>> ara.t.howard wrote:
>>> On May 9, 2008, at 6:08 PM, Paul Winward wrote:
>>>>
>>>> Note, I'm avoiding STDOUT.flush in sleep.rb since I won't be able to
>>>> change the actual scripts I'll be passing to popen3.
>>> 
>>> popen3 is going to be using fork/exec under the hood and should
>>> inherit the sync setting of STDOUT, so try setting
>>> 
>>>    STDOUT.sync = true
>>> 
>>> before the popen and see if that helps - untested, but i'm running out
>>> the door....
>>> 
>>> cheers.
>>> 
>>> a @ http://codeforpeople.com/

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