Re: stopping "wait" in (sub)script ?

[Zoltan Hidvegi <hzoli@ny.frontiercomm.net>]

I wrote:
> No.  The problem is that $(...) does not enter the new process to the
> process table.  $(<...) does not fork, so it is not surprising that it
> works.  The problem is that `cat ss` forks, and does an entersubsh after
> the fork().  When a process terminates the SIGCHLD handler calls
> update_job, which should reattach the terminal, but it does not do that
> since the terminated job was not in the process table so update_job() is
> not even called :-(.

I checked bash, ksh and pdksh, and all run command substituion in the same
process group as the shell.  This is logical, since a command substitution
cannot be backgrounded, and it solvs all the problems I described above,
plus some more.  The patch below should be applied on the top of my
previous patch (it does not depend on it, it just fixes an other bug).
What's also fix is:

% trap 'echo TERM' TERM
% echo `sh -c 'kill -TERM $$'`
TERM

As you see, the TERM trap is executed although the sell did not receive the
term signal, only the command substitution process terminated.  This
happened with all signals, not just SIGTERM (funny that bash has the same
bug, although only with the INT signal).

In most places where MONITOR is unset the terminal signals are set to
defaul.  This does not seems to be necessary here.  This copies the ksh93
behavious (pdksh and bash simply hangs when ^Z is pressed during command
substitution).  I have no idea why zsh need to change the SIGPIPE handler
when MONITOR is changed.  Anyone who knows better, please explain.  I also
wonder if we should add these signal changes to dosetopt() when MONITOR is
(un)set.  Examining ksh, pdksh and bash it seems that an interactive shell
should get a new process group and attach the terminal to this process
group on startup and it shoud restore its original process group and
reattach the terminal to this process group upon exit or before exec.  Any
comments about this?  It would be helpful if someone could look up the
relevant informations from POSIX 2a UPE.

Zoltan


*** Src/signals.c	1997/05/08 07:16:47	3.1.2.4
--- Src/signals.c	1997/05/16 05:05:35
***************
*** 422,434 ****
  	    for (;;) {
  		if (pid == *procsubpid) {
  		    *procsubpid = 0;
! 		    if (WIFSIGNALED(status)) {
  			*procsubval = (0200 | WTERMSIG(status));
! 			if (WTERMSIG(status) == SIGINT)
! 			    kill(getpid(), SIGINT);
! 			else if (sigtrapped[WTERMSIG(status)])
! 			    dotrap(WTERMSIG(status));
! 		    } else
  			*procsubval = WEXITSTATUS(status);
  		    times(&shtms);
  		    goto cont;
--- 422,430 ----
  	    for (;;) {
  		if (pid == *procsubpid) {
  		    *procsubpid = 0;
! 		    if (WIFSIGNALED(status))
  			*procsubval = (0200 | WTERMSIG(status));
! 		    else
  			*procsubval = WEXITSTATUS(status);
  		    times(&shtms);
  		    goto cont;
*** Src/exec.c	1997/05/09 05:36:44	3.1.2.8
--- Src/exec.c	1997/05/16 06:31:45
***************
*** 2109,2116 ****
      child_unblock();
      zclose(pipes[0]);
      redup(pipes[1], 1);
      entersubsh(Z_SYNC, 1, 0);
-     signal_ignore(SIGTSTP);
      execlist(list, 0, 1);
      close(1);
      _exit(lastval);
--- 2109,2116 ----
      child_unblock();
      zclose(pipes[0]);
      redup(pipes[1], 1);
+     opts[MONITOR] = 0;
      entersubsh(Z_SYNC, 1, 0);
      execlist(list, 0, 1);
      close(1);
      _exit(lastval);
***************
*** 2233,2240 ****
  
      /* pid == 0 */
      redup(fd, 1);
      entersubsh(Z_SYNC, 1, 0);
-     signal_ignore(SIGTSTP);
      execlist(list, 0, 1);
      close(1);
      _exit(lastval);
--- 2233,2240 ----
  
      /* pid == 0 */
      redup(fd, 1);
+     opts[MONITOR] = 0;
      entersubsh(Z_SYNC, 1, 0);
      execlist(list, 0, 1);
      close(1);
      _exit(lastval);