Run system command in ruby and interact with it

Question

I need to run a command on the command-line that asks for a user response. In case it helps the command is:

gpg --recipient "Some Name" --encrypt ~/some_file.txt

when you run this, it warns about something then asks:

Use this key anyway? (y/N)

Responding 'y' let's it finish correctly. I have been trying to use the open4 gem but I have not been able to get it to specify the 'y' correctly. Here is what I tried:

Open4::popen4(cmd) do |pid, stdin, stdout, stderr|
  stdin.puts "y"
  stdin.close

  puts "pid        : #{ pid }"
  puts "stdout     : #{ stdout.read.strip }"
  puts "stderr     : #{ stderr.read.strip }"
end

What am I doing wrong? Is what I am doing even possible?

Answer 1

The Unix way to handle these situations is with expect, which Ruby comes with built-in support for:

require 'pty'
require 'expect'

PTY.spawn("your command here") do |reader, writer|
  reader.expect(/Use this key anyway/, 5) # cont. in 5s if input doesn't match
  writer.puts('y')
  puts "cmd response: #{reader.gets}"
end

Answer 2

gpg is probably opening the terminal device directly to ask the user the question -- this is a common safety approach to prevent driving a script entirely from files. (See the now-deprecated getpass(3) routine for something similar.)

If you don't actually care enough about the warning to read it, you might as well use the gpg command line option --yes:

   --yes  Assume "yes" on most questions.