Re: AT_CHECK_INTERACTIVE

[Ralf Wildenhues]

Hello Paul,

A progress update, just FYI.

* Paul Eggert wrote on Sun, Dec 17, 2006 at 07:27:35AM CET:
> Ralf Wildenhues <address@hidden> writes:
> 
> >   mkfifo at-fifo-err
> >   mkfifo at-fifo-out
> >   command='{ sleep 2; echo out ; echo err >&2; sleep 2; exit 42; }'
> >   ( exec >at-fifo-out 2>at-fifo-err ; eval "$command" ) & at_cmd1=$!
> >   tee < at-fifo-out stdout & at_cmd2=$!
> >   tee < at-fifo-err stderr & at_cmd3=$!
> >   wait $at_cmd2 $at_cmd3 $at_cmd1
[...]

> Sure, just use pipes.  You shouldn't need any of the stuff with fifos
> and sleeps and wait.  It will be a bit of a pain to save $command's
> exit status, given that $command's output will be piped, but you can
> use something like the following trick (taken from zgrep):
> 
>       # Fail if either grep or sed fails.
>       exec 3>&1
>       r=`
>       exec 4>&1
>       (grep "$pattern" 4>&-; echo $? >&4) 3>&- | sed "$sed_script" >&3 4>&-
>       ` &&
>       exit $r

Hmm.  This is what I've been able to come up with for now.  Note
$at_cmd is an example command, in order to facilitate testing.
The sleep is just there to inspect progress easily.

  at_cmd='{ echo out; echo err >&2; sleep 2; exit 42; }'
  # The following is what AT_CHECK_MONITOR would do (not Ultrix-safe):
  exec 4>&1 5>&2
  at_res=`
    exec 3>&1
    ( ( (eval "$at_cmd") 3>&- 4>&- 5>&-; echo $? 1>&3) 2>&5 \
      | tee at-stdout 3>&-) 5>&1 1>&4 | tee at-stderr 3>&- 1>&2 5>&-
    `
  exec 4>&- 5>&-
  exit $at_res

This is probably still both buggy and too complicated, but it seems to
work.  I'm not sure whether closing all those fds is needed -- really
only fd leakage to $command would be a problem, I guess?  And while
we're at that topic, isn't that then an issue for many other things
that, say, configure usually executes?

FWIW, with a at-status file it simplifies to

  command='{ echo out; echo err >&2; sleep 2; exit 42; }'
  rm -f at-status at-stdout at-stderr
  exec 3>&1 4>&2
  ( ( (eval "$command") 2>&4 3>&- 4>&-; echo $? >at-status) |
    tee at-stdout) 4>&1 >&3 | tee at-stderr >&2 4>&-
  exec 3>&- 4>&-


I'm a bit afraid this warning in autoconf.info(File Descriptors):
|    Don't rely on open file descriptors being open in child processes.
| In `ksh', file descriptors above 2 which are opened using `exec N>file'
| are closed by a subsequent `exec' (such as that involved in the
| fork-and-exec which runs a program or script). [...]

may torpedo this nice idea; not to speak of Ultrix, of course.

> By the way, the name AT_CHECK_INTERACTIVE confused me, since I assumed
> it was testing an interactive program, or was a test you could run
> interactively.  Perhaps a better name would be AT_CHECK_MONITOR (or
> AT_CHECK_IMPATIENTLY :-)?

I like the last one ;-)  but AT_CHECK_MONITOR is probably better.

Thanks.  I may turn this into an actual patch eventually...

Cheers,
Ralf