On Tue, Jul 31, 2012 at 4:55 AM, Greg Wooledge <wool...@eeg.ccf.org> wrote: > On Mon, Jul 30, 2012 at 02:17:15PM -0700, Andrew Resch wrote: >> I am attempting to use exec and tee to have my scripts >> stdout/stderr appended to a log file like such: exec > >(tee -a $LOG) >> 2>&1 >> These scripts will often call other scripts with a similar >> exec statement, often writing to a separate log file. On my GNU/Linux >> systems, >> these scripts will run just fine without any issue, but on >> HP-UX they seem to hang or not display any output. > > The major difference here is that bash on HP-UX implements process > substitutions (the <() syntax) with a named pipe, whereas on Linux > it uses a /dev/fd/* file. > >> $ cat test_exec1.sh >> #!/bin/bash >> >> LOG="test_exec.log" >> exec > >(/usr/bin/tee -a $LOG) 2>&1 >> >> echo "i am exec1.." >> >> ./test_exec2.sh >> >> echo "i am done in exec1.." > >> $ while true; do ./test_exec1.sh; done > > You are opening a slew of named pipes and background jobs in rapid > succession, and not waiting for the jobs to finish. (It might still be > considered a bug... I'm just pointing out the practical aspects.) > I would bet that putting a "sleep 1" in the loop would make the problem > stop happening, as horrible a hack as that may be.
Yes, fair enough. I did the loop to simply make the issue more apparent, but many times I couldn't even run the test_exec1.sh script once successfully on one of my hosts. In those cases I'm not sure how large of a sleep I'd need to make it work ;) > I discuss this a bit on <http://mywiki.wooledge.org/BashFAQ/106>. The > only way to ensure clean operation is to avoid the <() syntax altogether > and use your own explicit named pipe and background job. Then you can > close the pipe and wait for the background job to terminate before > exiting. Thank you for this. I have removed the process substitution from my scripts and replaced it with using explicit named pipes, and now everything is working as expected.
