Re: Comparing strings

On 7/13/21 11:46 AM, ELCV wrote:
> Hello

Hi,

> I can't get this right. What I have is a script to backup VM 
> guests. The command is called with an argument, for example:
> 
> /usr/local/bin/vm-backup.sh FOO
> 
> Some of the VMs have two disks and I want to back them both up. Two of 
> the VMs have vert large data partitions that are backed up separately 
> and I want to exclude them.

Okay.  That sounds like some VMs can use a default, some need slightly 
different, and still others need something special.

> If I do this:
> 
> if [ "$1" != "FOO" ];
>   then
>         echo "I can backup the 2nd volume";
> else
>          exit;
> fi
> 
> It works. But if I add an "or" condition as follows:
> 
> if [ "$1" != "FOO" ]   ||  [ "$1" != "BAR" ] ;
>   then
>         echo "I can backup the 2nd volume";
> else
>          exit;
> fi
> 
> It fails.

ORed negative logic is ... tricksy.

> I have tried this a number of different ways and I can't get it. Any 
> guidance is appreciated. Thanks.

I would be tempted to try a case statement:

case ${1} in
	FOO)
		# FOO's specific backup.
	BAR|BOB)
		# specific backup for BAR and BOB.
	*)
		# default backup for all other systems.
esac

I also find that such a case statement is a lot easier to maintain long 
term as systems are added / changed / removed.

Depending on how the backups work, you might consider breaking out the 
actual backup actions to their discrete steps and call them as a 
function.  E.g. FOO would call functions 1 and 2, while BAR & BOB call 
functions 2 and 3, and then everyone else would only call functions 1 
and 3.  Use the case as a method to choosoe which pieces to run and then 
call the necessary common pieces.



-- 
Grant. . . .
unix || die