From: Doug Beaver <doug@...>
Date: 2003-03-07T12:24:22+09:00
Subject: pty & signals with wrapped shell

hello,

for fun, i am trying to use PTY to wrap my shell.  i adapted script.rb
from ext/pty and can run and exit my shell okay, but i'm having trouble
getting the signals to work correctly.  i can start up the shell, run 
ps and vi, and do some basic shell comands, but i can't interrupt or
suspend any jobs started by the shell.

when i call PTY.spawn, it gives me the pid of my shell.  i put a trap
call in my ruby code to grab sigint and sigstop and send those onto the
shell's pid, but i'm pretty sure i need to send those signals to
whatever subprocess my shell is currently running.  

i've already written a class that parses ps output and lets me query the
process stack, but it's pretty heavy and i'd rather not use it unless i
have to.  i'm hoping that there is a cleaner way to do this in pure
ruby, parsing ps or /proc feels like i'm using too much brute force.  i
like how short the current code is, so is there a ruby way to route the
signal properly?

if you're wondering why i'm doing this, i thought it would be fun to
create a ruby program that runs a shell and lets you filter the input
and output of the shell with ruby plugins.  when you hit enter after
entering a command on the prompt, your command is compared and if it
matches any plugins, they are ran instead of the command being passed to
the shell.  i don't know if it's possible but it sounded like it would
be fun to experiment with...

thank you,

doug

p.s.  i'm running ruby-1.8.0-preview2 compiled on os x 10.2.


#!/usr/bin/env ruby

require 'pty'

input, output, pid = nil, nil, nil
shell = ENV['SHELL']
if shell =~ /[^\w\/.]/ || !File.stat(shell).executable?
  raise "ENV[SHELL] must be a valid shell path!"
  exit 1 # never reached
end 

# sending the signal to the shell doesn't do it, i need to send the
# signal to the process the shell is currently running.  not sure
# how to do that...

%w/INT STOP/.each do |signal|
  trap(signal) do
    if pid
#      kill(signal, pid)
    end
  end
end

begin
  system "stty -echo raw lnext ^_"
  input, output, pid = PTY.spawn(shell)
  puts "input, output, pid = #{input}, #{output}, #{pid}"
  Thread.new do
    while true
      output.print STDIN.getc.chr
      output.flush
    end
  end
    
  begin
    while true
      c = input.sysread(512)
      break if c.nil?
      print c
      STDOUT.flush
    end
  rescue
  end
rescue
  STDERR.puts "general pty exception: #{$!}"
ensure
  # sometimes first stty call fails, don't know why...
  system("stty echo -raw lnext ^v") || system("stty -raw")
  input.close
  output.close
  Process.kill(0, pid) && Process.kill(9, pid)
end

-- 
"Contrary to what most people say, the most dangerous animal in the
world is not the lion or the tiger or even the elephant.  It's a shark
riding on an elephant's back, just trampling and eating everything they
see." -- Jack Handey