UNIX for Dummies Questions & Answers

Hi all,

i need a equivalent for the statement i run in bash, so it would also run in other shells. Specially i need it for ksh to run on AIX.
Here the statements:

exec > >(tee -a $log)
exec 2> >(tee -a $log >&2)

Thanks.

The 'script' command may be what you are looking for. It's usually used from outside a script.

You are right, but that's not what i'm looking for. The statement i posted i use inside the script, actually this are the first lines of the script.

I'm not sure this ever did quite what you thought. It could certainly change the perceived order of stdout/stderr. The two different, separate tees are liable to stomp on each other's lines. And this may interfere with redirections run outside the script, too. It's only a strange concidence of how bash works that gives this the appearance of working under some circumstances, but it also did weird things like catching prompts...

Potentially changing the order stdout/stderr come in order is inevitable when doing this, and doing this reliably is always cumbersome since it's supposed to be done from the outside.

This is the shortest "reliable" one I've yet seen managed:

Code:

#!/bin/ksh

log=ksh.log

rm -f $log /tmp/$$-e /tmp/$$-o /tmp/$$-m
mkfifo /tmp/$$-o /tmp/$$-e /tmp/$$-m || exit 1

(       tee /tmp/$$-m /dev/tty < /tmp/$$-o & # will wait for exec >
        tee /tmp/$$-m /dev/tty < /tmp/$$-e & # will wait for exec 2>
        cat < /tmp/$$-m > $log &             # will wait for $$-m
        ) >/dev/null

exec > /tmp/$$-o        # First tee will start running
exec 2>/tmp/$$-e        # Second tee will start running
while [ ! -e "$log" ] ; do true ; done
rm -f /tmp/$$-o /tmp/$$-e /tmp/$$-m

echo "stdout stuff"
echo "stderr stuff">&2

There's shorter/simpler versions using tail -f, to just print the output file instead of catching it midway, but it's possible for them to skip output and hang, not to mention all your output ends up going to stdout. The worst this one will do is reorder stderr/stdout and possibly print a line on your prompt after it quits -- unfortunately inevitable unless you're prepared to make a lot of guarantees about what your code will and won't be doing with traps and stdin/stdout/stderr. Right now this shouldn't interfere with those.

You can trade off one less fifo for one more subshell:

Code:

#!/bin/ksh

log=ksh.log

rm -f $log /tmp/$$-e /tmp/$$-o
mkfifo /tmp/$$-o /tmp/$$-e || exit 1

(       (       cat < /tmp/$$-o & # will wait for exec >
                cat < /tmp/$$-e & # will wait for exec 2>
                wait        ) | tee $log ) >/dev/tty &

exec > /tmp/$$-o        # First cat will start running
exec 2>/tmp/$$-e        # Second cat will start running
rm -f /tmp/$$-o /tmp/$$-e # Both ends guaranteed open now, so delete as early as possible

echo "stdout stuff"
echo "stderr stuff">&2

Thanks, nice sugestions. I decided to go the real simple way and just wrap my code in () and add 2>&1 | tee $log at the very end.