CODEWITHSUNDEEP
rubylinux
Pieter Jacobs
Pieter Jacobs

Reputation: 85

Read STDOUT and STDERR from subprocess continiously

I'm using IO.popen to start a subprocess, but I only get the result of everything that happened in the time it took for the subprocess to run (sometimes 5 minutes or whatever) when the subprocess exits. I really need to be able to see everything the subprocess writes to stderr and stdout as-and-when it happens.

So far I could not find anything that works like this, but I'm sure it's possible.

Upvotes: 7

Views: 1459

Answers (2)

Victor Deryagin
Victor Deryagin

Reputation: 12225

You might want to use Open3.popen3 from standard library, it gives access to stdin, stdout, and stderr as streams.

Upvotes: 0

user904990
user904990

Reputation:

if you need to get output in real time i would recommend to use stdlib PTY instead of popen

something like this:

require 'pty'

cmd = 'echo a; sleep 1; cat /some/file; sleep 1; echo b'
PTY.spawn cmd do |r, w, pid|
  begin
    r.sync
    r.each_line { |l| puts "#{Time.now.strftime('%M:%S')} - #{l.strip}" }
  rescue Errno::EIO => e
    # simply ignoring this
  ensure
    ::Process.wait pid
  end
end
exit "#{cmd} failed" unless $? && $?.exitstatus == 0

> 33:36 - a
> 33:37 - cat: /some/file: No such file or directory
> 33:38 - b

this way you get output instantly, just as in terminal

Upvotes: 7

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