From: Dave Thomas <Dave@...>
Date: 2001-07-30T09:19:12+09:00
Subject: [ruby-talk:18770] Re: Autoflush backquotes??

Chris Moline <ugly-daemon@home.com> writes:

> I am trying to get the backquotes to print everything "as it comes"
> instead of after the backquotes are done. Does anyone have any idea
> how to do this?? Using $stdout.sync = true does not work. Here is
> the relevant part of the script

You won't be able to use backquotes here, because backquotes wait for
all the output to appear before returning (as that's what they are
intended for).

Instead, you can open a pipe to the child process and read it's output
interactively.

     IO.popen(command) do |p|
       p.each do |line|
         puts line
       end
     end

However, there's a further wrinkle. Often, programs that produce output
line-by-line when you run them interactively change their behavior
when run as a subprocess talking to a pipe. For example, here's a
simple Ruby program:

     5.times do
       puts "hello"
       sleep 1
     end

Run it form the command line, and it does what you expect. However,
run it as the command in the popen example above, and you won't see
any output until it finishes. You need to change it to

     $stdout.sync = true
     5.times do
       puts "hello"
       sleep 1
     end

To get it to write the output as it's produced.

Regards


Dave