UNIX for Dummies Questions & Answers

Ok, so now at the end, check/show the return code of the ls command ?

Code:

#!/bin/ksh
touch test.file
LOG=./tmp.log
(
        echo "Hello world"
        ls -ltr test.file
        echo "Goodbye world"
) 2>&1 | tee ${LOG}

echo "Return code is: ???"

I've tried just capturing it inside that block, but accessing it outside the brackets fails (null value).

You said you wanted to capture everything in the script in the log file. So you've changed the rules again... grumble, grumble, grumble...

Code:

#!/bin/ksh
touch test.file
AFTERLOG=./$$.after.log
LOG=./tmp.log
(
        echo "Hello world"
        echo "1st echo return code is: $?" > "$AFTERLOG"
        ls -ltr test.file
        echo "Return code is: $?" >> "$AFTERLOG"
        echo "Goodbye world"
        echo "2nd echo return code is: $?" >> "$AFTERLOG"
) 2>&1 | tee "${LOG}"
cat "$AFTERLOG"
rm -f "$AFTERLOG"

This is what has been happening in your original code ...

When tee opens the fifo for reading, if no other process has yet written to the fifo, tee will block (hang/sleep) until another process opens the fifo and writes to it.

Each echo statement will attempt to open the fifo, write to it, and then close it. Most likely, when this succeeds, it is because both echoes have written to the fifo before tee has a chance to read it.

Adding ls greatly increases the chances of tee reading between the echoes. If that happens, after reading the first echo's text, tee will detect EOF and exit. When the second echo opens the fifo for writing, it will hang until something opens the fifo for reading (which will never happen with your sample script).

exec 5>fifo prevents the hang by ensuring that there is always a write file descriptor for the fifo. That descriptor is never used, but since it has permission to write, so long as it exists, tee will not read EOF; instead, tee will block until someone writes (in this case, the second echo).

Regards,
Alister

apologies, I only changed the rules once I editted my original post after your first post, and clarified the two things I'm trying to do.

hmm, that "sort of" works, but then I have to go digging the error code out of the script and stuff it into a variable if I need to use it / check it.

Thanks ... I think what I found with the exec 5>&PIPE seems to work more consistently.
And it seems from the responses, that another (cleaner) option probably doesn't exist.

Don't want to take any more of your time Sorry for confusion, thanks for help. I think I have something working, and I think I understand what's going on.

Cheers!