From: Simon Strandgaard <0bz63fz3m1qt3001@...>
Date: 2003-05-15T21:14:00+09:00
Subject: Re: RCR for child execution

On Thu, 15 May 2003 18:29:50 +0900, ts wrote:

>>>>>> "S" == Simon Strandgaard <0bz63fz3m1qt3001@sneakemail.com> writes:
> 
> S> I think my proprosal a minor patch  and I think its possible.
> 
>  Well, it's easy : #system is
> 
>   rb_define_global_function("system", rb_f_system, -1);
> 
>  If you don't like it, you write your own version and then you call
>  rb_define_global_function() to change the definition of #system
> 
>  Then you do the same with fork, and backquote

OK.. I have now replaced 'system' with a system which can redirect output
elsewhere.  I use pipes + threads so that stdout/stderr can go to a
string.  BTW: people said that this was *impossible* :-)

I don't think my code here will interfere with the output of C/C++. 
Still I need to overload Kernel#fork, Kernel#backquote and stdin is not
yet supported. What should I change on my version of 'system' so that it
gets same behavier as rubys 'system'.. arguments/return value ???

> cat b.rb
require 'stringio'
require 'singleton'

class Redir
        include Singleton
        def initialize
                @out = $stdout
                @error = $stderr
        end
        def set_out(elsewhere)
                @out = elsewhere
        end
        def set_error(elsewhere)
                @error = elsewhere
        end
        def write_out(msg)
                msg = msg + "_"
                @out.write(msg)
        end
        def write_error(msg)
                msg = msg + "."
                @error.write(msg)
        end
end

def system(command)
        # todo: stdin
        r1, w1 = IO.pipe # stdout
        r2, w2 = IO.pipe # stderr
        thread1 = Thread.new do  # redirect stdout
                loop do
                        s = r1.read(1) # TODO: can I make this buffered?
                        Redir.instance.write_out(s)
                end
        end
        thread2 = Thread.new do  # redirect stderr
                loop do
                        s = r2.read(1) # TODO: can I make this buffered?
                        Redir.instance.write_error(s)
                end
        end
        if (pid = fork) == nil
                r1.close; r2.close
                $defout = w1; $stdout = w1; $stderr = w2
                #puts "system: enter: #{command}"
                exec(command)
        end
        w1.close; w2.close
        Process.waitpid(pid)
        r1.close; r2.close
        thread1.kill; thread2.kill
        #puts "system.leave"
end

redir = Redir.instance

s = ""
buf = StringIO.new(s, "w")
redir.set_out(buf)
redir.set_error(buf)
system("ls main.cpp nonexist")

puts "1"
puts s.split(/\n/).collect { |msg| "OK: "+msg }.join("\n")
puts "2"
>

Output looks like this:

> ruby b.rb
1
OK: l.s.:. .n.o.n.e.x.i.s.t.:. .N.o. .s.u.c.h. .f.i.l.e. .o.r. .d.i.r.e.c.t.o.r.y.
OK: .m_a_i_n_._c_p_p_
OK: _
2
>


--
Simon Strandgaard