Help with bash script

KFC123 · 07-01-2009, 06:19 PM

I am writing a simple script to do the following: mount a certain volume in, copy some files to that volume and then umount it

mount /dev/hda1 /mnt
# if error here, echo "error 1"
cp /home/jay/cifi /mnt -r
# if error here, echo "error 2"
umount /dev/hda1
# if error here, echo "error 3"

But for these three command, I would like to check each step is going well, no error. So how can I check that?

pixellany · 07-01-2009, 06:32 PM

Look at the man page for "mount"---specifically the RETURN CODES near the end. Basically, you need to test the return code and branch based on the result.

Note:

1. You normally don't want to mount something at "/mnt". That would hide everything else in the directory.

2. What is this supposed to do?:
cp /home/jay/cifi /mnt -r
The normal syntax is:
cp [OPTION]... SOURCE... DIRECTORY

AND---please confirm if this is homework.

micxz · 07-01-2009, 06:33 PM

You can check if the exit status of a previously executed command by checking if the var $? is equal to zero.

Something like:
if [ "$?" = "0" ] ; then
echo "success"
else
echo "failed"
fi

btw your cp command looks like it should be:
cp -r ... instead of the cp ... -r

KFC123 · 07-01-2009, 06:42 PM

Quote:

Originally Posted by pixellany

Look at the man page for "mount"---specifically the RETURN CODES near the end. Basically, you need to test the return code and branch based on the result.

Note:

1. You normally don't want to mount something at "/mnt". That would hide everything else in the directory.

I just show an example, not really using /mnt

Quote:

2. What is this supposed to do?:
cp /home/jay/cifi /mnt -r
The normal syntax is:
cp [OPTION]... SOURCE... DIRECTORY

Thanks for remind me this, but it works and ... just wonder why it didn't even report a warning?

Quote:

AND---please confirm if this is homework.

Absolutely NOT. I am writing a script to backup a given directory to a disk and run it with cron constantly.

micxz · 07-01-2009, 06:56 PM

Quote:

Originally Posted by KFC123

I am writing a script to backup a given directory to a disk and run it with cron constantly.

You may want to look into rsync is you want to keep the backup files in sync rather then cp as you will have copies of old deleted or unused files in your backup. And it's lighter on you system as it will only copy new or changed files.

pixellany · 07-01-2009, 07:01 PM

Quote:

Thanks for remind me this, but it works and ... just wonder why it didn't even report a warning?

How about that!!

Quote:

AND---please confirm if this is homework.
Absolutely NOT.

OK

Looking at the other reply, there's another form to consider:

if $(mount something somewhere); then
do this
else
do that
fi

KFC123 · 07-01-2009, 07:07 PM

Thanks all of you. It helps

jlliagre · 07-01-2009, 07:29 PM

Quote:

Originally Posted by pixellany

Looking at the other reply, there's another form to consider:

if $(mount something somewhere); then
do this
else
do that
fi

and the slightly simpler:

Code:

if mount something somewhere ; then
   do this
else
   do that
fi

and the even simpler:

Code:

mount something somewhere && do this || do that

eg:

Code:

mount /dev/hda1 /mnt && echo "mount hda1 done" || echo "error 1"

Hobbletoe · 07-02-2009, 07:45 AM

Even shorter might be ...

Code:

mount /dev/hda1 /mnt || exit 1
cp /home/jay/cifi /mnt -r || exit 2
umount /mnt || exit 3

This acts as a mini if statement.

if_statement && do_this_when_true || do_this_when_false

If you want it to be more informative when an error occurs, try the following. Please note the spaces around the braces, and the semi-colon after each command.

Code:

mount /dev/hda1 /mnt || { echo Error mounting device.; exit 1; }
cp /home/jay/cifi /mnt -r || { echo Error copying files.; exit 2; }
umount /mnt || { echo Error unmounting device.; exit 3; }