topic Re: Tar with Shell Scripts in Operating System - HP-UX

Tar with Shell Scripts

Robert True — Tue, 07 Sep 2004 10:07:06 GMT

I am trying to verify ignite tapes after writing with a ksh script and email the results, but I cannot manage to send the read of the tar archive on the tape to /dev/null so that it does not appear in the out going email.

Everything else is working, I know the ignite boot blocks are good, etc, it's just the tar archive read back that is the problem: too verboose. A pain to read at best, and usually gets trunciated by the MS exchange system anyway. Unfortunatly the read-back of the boot block is then lost also.

The vfy cmd used is:
/bin/tar tf /dev/rmt/0m 2>&1 > /dev/null

If I recall correctly from the very distant past, tar does not send the output to standard err under this situation, but how can I trap it? Any suggestions?

Thanks Rt.

Re: Tar with Shell Scripts

harry d brown jr — Tue, 07 Sep 2004 10:35:26 GMT

To get error messages just PRETEND to restore a BOGUS file:

tar -xvf /dev/rmt/0m crazymanfilename 2>&1 | uuencode errors.txt | mailx -m -s "tar er
rors" youremail@yourdomain.com

You can get errors like:
tar: cannot open nxewtest.tar
or
Tar: error! blocksize changed
or whatever

live free or die
harry

Re: Tar with Shell Scripts

Steven E. Protter — Tue, 07 Sep 2004 10:38:58 GMT

I would suggest on a spot with some free space

tar tf /dev/rmt/0m > testfile.txt

SEP

Re: Tar with Shell Scripts

Olivier Decorse — Tue, 07 Sep 2004 10:40:03 GMT

ok,
2 possibilities :
1) after the tar command, verify the return status of the command (under ksh) :
/bin/tar tf /dev/rmt/0m 2>&1 > /dev/null
STATUS=$?
if [ $STATUS -ne 0 ]
then
echo "Problem with tar on `hostname`" |mailx -m -s "pbl with tar" your_name@your_address
fi
tar only retuns 0 if everything is ok ! I test with modifying an tar file and it returns : 3

2) modify your command line to extract any error :
/bin/tar tf /dev/rmt/0m > /dev/null 2> error_tar.txt
if [ -s error_tar.txt ]
then
echo "Problem with tar on `hostname`" |mailx -m -s "pbl with tar" your_name@your_address
fi
With my previous manually modification, error_tar.txt contains :
Tar: tape blocksize error

Hope this helps you !

Olivier.

Re: Tar with Shell Scripts

Sundar_7 — Tue, 07 Sep 2004 11:52:10 GMT

The problem is the order in which stdout and stderr is redirected.

Try this

/bin/tar tf /dev/rmt/0m >/dev/null 2>&1

This should work.

Re: Tar with Shell Scripts

Jeroen Peereboom — Tue, 07 Sep 2004 12:07:34 GMT

You command should read
/bin/tar tf /dev/rmt/0m > /dev/null 2>&1

Or maybe even ..../dev/rmt/0mn .... for no-rewind device.
You may also send the output to a file, and send a line count (wc -l) in an email?
And the return code of the tar command too.

JP.

Re: Tar with Shell Scripts

Bill Hassell — Tue, 07 Sep 2004 13:28:12 GMT

Just to explain why "2>&1 > /dev/null" and "> /dev/null 2>&1" are very different, this is what is happening: The shell processes file redirection left to right so 2>&1 >/dev/null says: take whatever stdin (descriptor #1) is and set stdout to the same fd. Then >/dev/null changes stdout to /dev/null but stderr is still going to whatever stderr was in the beginning. The effect (assuming default conditions) is that stdout goes to /dev/null and stderr goes to the terminal display.

In the second case, >/devnull changes stdout, then 2>&1 change stderr to match the current state of stsout, which is /dev/null. Note that there will be no output at all which not what is desired. I would redirect stderr into your email message and let stdout go to your email. That way, you'll get the tar error messages but the table of contents will be sent to /dev/null.

One other note: /bin has been gone for more than a decade. Just like Solaris and other SysV Unices, the v.4 filesystem layout has obsoleted /bin and /lib. They are now /usr/bin and /usr/lib. The reason things seem to work OK is through the use of transition links:

ll -d /bin /lib
lr-xr-xr-t 1 root sys 8 Oct 29 2003 /bin@ -> /usr/bin
lr-xr-xr-t 1 root sys 8 Oct 29 2003 /lib@ -> /usr/lib

These are "transition" links (hint, hint) and may not be installed in future versions of HP-UX.

Re: Tar with Shell Scripts

Sundar_7 — Tue, 07 Sep 2004 16:28:27 GMT

============================================2>&1 >/dev/null says: take whatever stdin (descriptor #1) is and set stdout to the same fd. Then >/dev/null changes stdout to /dev/null but stderr is still going to whatever stderr was in the beginning
============================================

With all due respect, I believe Bill intended to say this :-)

============================================
2>&1 >/dev/null says: take whatever stdout (descriptor #1) is and set stderr to the same fd.Then >/dev/null changes stdout to /dev/null but stderr is still going to whatever stdout was in the beginning
============================================

Re: Tar with Shell Scripts

Bill Hassell — Tue, 07 Sep 2004 22:04:16 GMT

Thanks Sundar. Redirection based on redirection really needs some arrows and drawings. ;-}

Re: Tar with Shell Scripts

Robert True — Wed, 29 Sep 2004 10:18:39 GMT

Thanks for all the comments, esp. the hints on redirection, but the tar command uses fd3 to output the list of files and because of the nesting of the shell scripts being used, I have not been able to trap it yet. I am Closing the thread as you ave gotten me on the right track, and I do not currently have time to work on it further.

Thanks again!

Rt.

Re: Tar with Shell Scripts

Robert True — Wed, 29 Sep 2004 10:19:40 GMT

See my last posting.

Rt.