Getting the terminal while in the background.

Pierre A. Humblet pierre.humblet@ieee.org
Mon Oct 4 19:11:00 GMT 2004


Chet Ramey wrote:
> 
> > Under Cygwin, the command below gives rise to a warning:
> >
> > ~: true | `echo true` &
> > [1] 380723
> > ~: Use "logout" to leave the shell.
> > [1]+  Done                    true | `echo true`
> >
> > I found the explanation, please bear with me.
> 
> Thanks for the detailed explanation.
> 
> > There are 4 processe involved:
> > the main interactive pid M
> > a subprocess A evaluating the first true,
> > a subprocess B evaluating `echo true',
> >   which still has "interactive" = 1,
> >   and forking a subprocess C that evaluates the second true.
> >
> > What's happening is that process B has
> > subshell_environment 0x18 = SUBSHELL_PIPE | SUBSHELL_FORK
> > Accordingly in command_substitute() it sees
> >   if ((subshell_environment & SUBSHELL_PIPE) == 0)
> >     pipeline_pgrp = shell_pgrp;
> > and it does NOT set pipeline_pgrp to shell_pgrp.
> > It then calls make_child() with async_p = 0.
> 
> This is the problem.  The code as written makes SUBSHELL_ASYNC and
> SUBSHELL_PIPE mutually exclusive; they are not.
> 
> Correcting this fixes the problem.

Thanks Chet.

You mean something like the following, or is there more to it?

@@ -2518,9 +2518,11 @@ execute_simple_command (simple_command, 
          already_forked = 1;
          simple_command->flags |= CMD_NO_FORK;
 
-         subshell_environment = (pipe_in != NO_PIPE || pipe_out != NO_PIPE)
-                                       ? (SUBSHELL_PIPE|SUBSHELL_FORK)
-                                       : (SUBSHELL_ASYNC|SUBSHELL_FORK);
+         subshell_environment = SUBSHELL_FORK;
+         if (async)
+            subshell_environment |= SUBSHELL_ASYNC;
+         if (pipe_in != NO_PIPE || pipe_out != NO_PIPE)
+            subshell_environment |= SUBSHELL_PIPE;
 
          /* We need to do this before piping to handle some really
             pathological cases where one of the pipe file descript

Pierre



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