From: pete@... (Peter J. Kernan)
Date: 2001-10-27T00:33:01+09:00
Subject: [ruby-talk:23468] expect.rb Child_changed

I am seeing a race condition w/the following program. Any guidance would
be appreciated. Here is a toy proof-of-concept program, wherein files
containing commands are fed in turn to an interactive program. Here is a
simple interactive program,

----------------------------reverse.rb -----------------------------------
#!/usr/bin/env ruby

loop {
  print "reverse> "
  repl = $stdin.gets
  exit unless repl
  repl.chomp!
  case repl
    when /^\s*exit\s*$/, nil
      exit
    else 
      puts repl.reverse
  end
}

--------------------------------------------------------------------------

here is the driver program
----------------------------reverse-expect.rb ----------------------------
#!/usr/bin/env ruby

require 'expect'
require 'pty'

exit unless ARGV[0]

ARGV.each {|file| 
  input = File.open(file)
  
  catch (:done) do
  PTY.spawn("./reverse.rb") do |r,w|
   w.sync = true
     loop {
       r.expect("reverse> ") { |out|
         $stdout.print out
         s = input.gets
         case s.strip
           when "exit"
             begin
    	       w.print s
    	     rescue
  	       $stdout.puts s
    	       throw :done
    	     end
           else
             w.print s
           end
       }
     }
   end
  end
}
--------------------------------------------------------------------------

the program may be called as in

~/tmp> ./reverse-expect.rb zip-frags
[...snipped output...]
reverse> I'm using my X-RAY VISION to obtain a rare glimpse of the
eht fo espmilg erar a niatbo ot NOISIV YAR-X ym gnisu m'I
reverse>  INNER WORKINGS of this POTATO!!
!!OTATOP siht fo SGNIKROW RENNI 
reverse> exit

but occasionally (order 10%) i see e.g.

reverse>  INNER WORKINGS of this POTATO!!
!!OTATOP siht fo SGNIKROW RENNI 
reverse> /usr/local/lib/ruby/1.6/expect.rb:17:in `getc': \
Child_changed: 9162 (RuntimeError)
        from /usr/local/lib/ruby/1.6/expect.rb:17:in `expect'
        from ./reverse-expect.rb:15
        from ./reverse-expect.rb:15:in `loop'

i am now trying the Expecter class Matz posted in [ruby-talk:01767,6436]
to see if i can write the program i want using his technique, but
independently of the success of that effort it would be useful to know
whether i am using expect.rb incorrectly in this instance.

~/tmp> ruby -v
ruby 1.6.4 (2001-06-04) [i686-linux]

  Pete
-- 
screwbean: a shrub or small tree found in the US Desert Southwest