topic Re: shell programming in Operating System - HP-UX

shell programming

Olga_1 — Tue, 08 Oct 2002 14:57:23 GMT

I need to capture the output of 'bdf|grep /mnt', if there is nothing, then do other tasks.

Is there a better way to hadle this, other then capturing the output to a file?

Re: shell programming

Ted Ellis_2 — Tue, 08 Oct 2002 15:03:25 GMT

you could pipe this output to awk instead of a file... and make the entire sting a variable that you can then check with an if loop

on my system the 6th field on a line returned from bdf is the mount point... if your /mnt is not mounted, it will not be returned and MNT_CHECK should be null.

MNT_CHECK = `bdf|grep /mnt | awk '{print $6}'`
echo ${MNT_CHECK} # just to see if you get what you expect...

now set up some if statement that will verify your logic and execute other tasks...

Ted

Re: shell programming

steven Burgess_2 — Tue, 08 Oct 2002 15:03:34 GMT

Hi

You can check if the exit code was succesful

bdf | grep /mnt
if [ $? != 1 ]
then
task
fi

HTH

Steve

Re: shell programming

James R. Ferguson — Tue, 08 Oct 2002 15:03:55 GMT

Hi:

How about:

# bdf|grep -q /mnt && echo "It's mounted!"

Regards!

...JRF...

Re: shell programming

MANOJ SRIVASTAVA — Tue, 08 Oct 2002 15:10:18 GMT

export A=`bdf | grep /mnt `

if [ $A = 0 ]

then

command

exit

fi

Manoj Srivastava

Re: shell programming

Dietmar Konermann — Tue, 08 Oct 2002 15:17:15 GMT

I wonder, how $A could ever get "0"?

IMHO, James' approach is by far the coolest. :)

Re: shell programming

James R. Ferguson — Tue, 08 Oct 2002 15:22:53 GMT

Hi Olga:

The concept here is that no file is used. Rather the output of 'bdf' is piped to 'grep' which is run "quietly" (without output). The return code of grep is examined and only if it is non-zero then is your command (or commands as the example shows) executed:

# bdf|grep -q /mnt || ( echo "It's not mounted!";date )

You can exchange the double pipe (||) for a double ampersand (&&) and invert the logic.

Regards!

...JRF...

Re: shell programming

Olga_1 — Tue, 08 Oct 2002 15:30:31 GMT

James,

Thank you for the explanations.
I wanted to assighn you 10 points, but somehow it turned to 0. Can I modify it?

Re: shell programming

John Palmer — Tue, 08 Oct 2002 15:31:55 GMT

Checking /etc/mnttab would be quicker than running bdf.

I would also recommend changing your grep arguments to only match for a filesystem called /mnt. All the above examples would also match something like /mntxxx or even /dev/vgxx/mnt...

Something like:

if bdf | grep -q " /mnt$"
then...

or:

if grep -q " /mnt " /etc/mnttab
then...

Would do the trick.

Regards,
John

Re: shell programming

S.K. Chan — Tue, 08 Oct 2002 15:37:56 GMT

In addition to others .. a couple of ways ..

var=$(bdf|grep /mnt)
if [[ $var != "" ]]
then
# do your stuff here
fi

OR

if [[ $(bdf|grep /mnt|wc -l) -ne 0 ]]
then
# do your stuff here
fi

Take note that "bdf" command may hung if you got stale NFS filesystem or bad FS. I'm in favor of "mount -v" instead.

Re: shell programming

James R. Ferguson — Tue, 08 Oct 2002 15:45:54 GMT

Hi Olga:

Well, once you assign points there's no changing them! ;-)

John Palmer makes a very good point. You could leverage his suggestion like this too:

# grep -q "/mnt " /etc/mnttab || ( echo "It's not mounted!";date )

Notice that I let 'grep' open the '/etc/mnttab' rather than spawn a separate process to do so, like 'cat /etc/mnttab|grep...'.

...JRF...

Re: shell programming

Dietmar Konermann — Tue, 08 Oct 2002 16:05:31 GMT

Folks, I like this thread... what about

mount | grep -q '^/opt ' && echo "Yo, brother."

Should be more water-proof, I think. In general, I don't like reading /etc/mnttab directly.

Regards...
Dietmar.

Re: shell programming

James R. Ferguson — Tue, 08 Oct 2002 17:07:32 GMT

Hi Dietmar:

Das ist sehr gut!

Yes, I like that better. It's short, matches exactly what (and only what it should) and executes very quickly.

BTW, your new hat looks just like it was made for you! :-))

With warm regards...

...JRF...

Re: shell programming

Dietmar Konermann — Tue, 08 Oct 2002 18:24:21 GMT

Hi, James!

Vielen Dank fuer die Blumen! :)

Greetings to Sarasota.

Dietmar.