redirecting stdio/stderr from a suspended then bged job

redirecting stdio/stderr from a suspended then bged job

[Michael Barnes]

This has been bugging me for a while.  How can I suspend a job that is
taking longer than I expect and then put it in the background and then
redirect stdio and/or stderr to a file (or /dev/null) ?

example:

wget http://slowserver/bigfile.tgz

1% done and its been 2 minutes

^Z

zsh: 25317 suspended  wget http://slowserver/bigfile.tgz

bg %1 >/dev/null 2>&1

nope does not work that just redirects the output of bg not the job that
was bged.

Any suggestions? (besides using screen).

Michael Barnes

Re: redirecting stdio/stderr from a suspended then bged job

[Bart Schaefer]

Michael Barnes writes:
 > This has been bugging me for a while.  How can I suspend a job that is
 > taking longer than I expect and then put it in the background and then
 > redirect stdio and/or stderr to a file (or /dev/null) ?

You can't.  The I/O descriptors are all established before the job is
started the first time, and then once it is running they're completely
under the control of the job itself; the shell can't change them again.

If you think about it, it has to work this way; imagine the havoc that
could be wrought if a process couldn't guarantee that all writes to the
same descriptor are going to go to the same place.

The only thing you can do is to guess what jobs might take a long time,
and redirect their output somewhere when you start them.  If that place
is a file and you later want to see some of the output, you can run
"tail -f" or whatever.

There are some tricks you could play with named pipes or the zsh coproc,
but they all require that the redirection be specified when you first
type out the command.

Re: redirecting stdio/stderr from a suspended then bged job

[Geoff Wing]

Michael Barnes <mibarnes@vt.edu> typed:
:This has been bugging me for a while.  How can I suspend a job that is
:taking longer than I expect and then put it in the background and then
:redirect stdio and/or stderr to a file (or /dev/null) ?
:example:
:wget http://slowserver/bigfile.tgz
:1% done and its been 2 minutes
:^Z
:zsh: 25317 suspended  wget http://slowserver/bigfile.tgz
:bg %1 >/dev/null 2>&1
:nope does not work that just redirects the output of bg not the job that
:was bged.

You can't.  It's out of our control unless zsh was to keep running
just to keep the pipes going.

Of course, with recent wget you don't need to (if you use
the -v option) as it will automagically start writing to ``wget-log''
when it can't write to the tty any more.  Well, that's what happens
with me.  Maybe it needs another option.  BTW, the manual says it's
in -v mode by default, but without it I couldn't get it to go to
wget-log (when I tried just now).

Regards,
-- 
Geoff Wing   <gcw@pobox.com>            Mobile : (Australia) 0412 162 441
Work URL: http://www.primenet.com.au/   Ego URL: http://pobox.com/~gcw/