From: ahoward <ahoward@...>
Date: 2003-05-13T08:27:23+09:00
Subject: Re: RCR for child execution

On Tue, 13 May 2003, Brian Candler wrote:

> > The problem is fairly simple, but I doubt anyone understands me ???
>
> If I do understand you, then you are asking for something impossible. I
> think you would realise this if you understood the Unix execution
> environment a little better.

perhaps i too am misunderstanding, but it does not seem like what simon is
asking for is impossible - there is another option:

a process can redirect fd 1 and 2, call some methods (possibly which spawn
sub-processes), and restore fd 1 and 2.  i quite realize the entire
broken-pipe argument against this but considering simon's application - it
seems like this is moot (or at least not cared about).

AFAICT ruby does something odd which prevents this - 50 'i love ruby' stickers
to whomever can figure out why this short c program does not work for ruby!

it works for other types of output routines - what is ruby doing here?:

file: redirect2.c

----CUT----
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <assert.h>
#include "ruby.h"

/*
gcc redirect2.c -I /usr/local/ruby-1.6.6/ /usr/local/ruby-1.6.6/libruby.a -lm -ldl -lcrypt
*/

int
main (argc, argv)
     int argc;
     char **argv;
{
  int fd[2];
  int f;
  int __out, __err;
  pid_t pid;
  char *script;
  int c;

  assert ((script = argv[1]) != NULL || (script = "redirected.rb"));

  /* save */
  assert ((__out = dup (STDOUT_FILENO)) != -1);
  assert ((__err = dup (STDERR_FILENO)) != -1);

  /* redirect */
  assert (pipe (fd) == 0);
  assert (dup2 (fd[1], STDOUT_FILENO) != -1);
  assert (dup2 (fd[1], STDERR_FILENO) != -1);

  /* sandboxed */

  /* THIS WORKS... */
  system ("ls "__FILE__);
  system ("ls no-exist");
  write (STDOUT_FILENO, "redirected out\n", 15);
  write (STDERR_FILENO, "redirected err\n", 15);

  /* THIS WILL NOT... */
  /*
  ruby_init ();
  ruby_script (script);
  rb_load_file (script);
  ruby_run ();
  */

  /* restore */
  assert (dup2 (__out, STDOUT_FILENO) != -1);
  assert (dup2 (__err, STDERR_FILENO) != -1);


  /* display */
  write (STDOUT_FILENO, "REDIRECTED:\n", 12);
  assert (close (fd[1]) != -1);
  while (read (fd[0], &c, 1) && write (STDOUT_FILENO, &c, 1));
  assert (close (fd[0]) != -1);

  return (EXIT_SUCCESS);
}

/*
*
* file: redirected.rb **
*
`ls #{__FILE__}`
`ls non-existent-file`
system 'ls #{__FILE__}'
system 'ls non-existent-file'
STDOUT.puts 42
STDERR.puts 42
$defout.puts 42
$stdout.puts 42
$stderr.puts 42
puts 42
*/
----CUT----

notice the part which does not work has been commented out.

-a

--
  ====================================
  | Ara Howard
  | NOAA Forecast Systems Laboratory
  | Information and Technology Services
  | Data Systems Group
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  | Email: ara.t.howard@fsl.noaa.gov
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