Run shell command inside ruby, attach STDIN to command input

Question

I'm running a long-running shell command inside ruby script like this:

Open3.popen2(command) {|i,o,t|
  while line = o.gets
   MyRubyProgram.read line
   puts line
  end
}

So I would be able to look at the command output in the shell window.

How do I attach STDIN to command input?

Arie Xiao · Accepted Answer · 2014-04-20 14:35:37Z

1

You need to:

Wait for the user input from STDIN
Wait for the output of the command from the popen3 -- o

You may need IO.select or other IO scheduler, or some other multi-task scheduler, such as Thread.

Here is a demo for the Thread approach:

require 'open3'

Open3.popen3('ruby -e "while line = gets; print line; end"') do |i, o, t|
  tin = Thread.new do
    # here you can manipulate the standard input of the child process
    i.puts "Hello"
    i.puts "World"
    i.close
  end

  tout = Thread.new do
    # here you can fetch and process the standard output of the child process
    while line = o.gets
      print "COMMAND => #{line}"
    end
  end

  tin.join    # wait for the input thread
  tout.join   # wait for the output thread
end

edited Apr 20, 2014 at 14:35

answered Apr 20, 2014 at 14:05

Arie Xiao

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6 Comments

Art Shayderov Over a year ago

I'm reluctant to use your code because I have no experience with thread synchronization in Ruby. Basically, I just want to be able to process output programmatically and to interact with the shell while I'm at it. Isn't there a simpler way to do that? What if I launch the shell and redirect a copy of output with tee to my program? Will it solve my problem?

Arie Xiao Over a year ago

@ArtShayderov I've updated the demo a bit and added some comment. You can save it to a Ruby file and test it. It should be clear where to manipulate the standard input and where to process the standard output now.

Art Shayderov Over a year ago

So I put reading STDIN inside tin block like that STDIN.each_char {|c| i.puts c}?

Arie Xiao Over a year ago

@ArtShayderov Yes. Make sure 1) You terminate the input by EOF after you finish typing, that is, Ctrl-Z on windows or Ctrl-D on Linux. 2) You close the standard input of the child process (i.close) before you leave the tin block.

Art Shayderov Over a year ago

It works. But I'm testing different commands in linux and some of them (e.g. top) fail with message failed tty get.

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