working with tar exclude command

i have issue with tar, let me explain

when i run below command it works perfectly as usual.

tar -cvf /tmp/temp.tar --exclude="exclusion expression" dir

my requirement is

--exclude="exclusion expression"

will come from another variable.
so when i execute below command:

tar -cvf /tmp/temp.tar "$patern" dir

it interprets it as

tar -cvf /tmp/temp.tar '--exclude="exclusion expression" ' dir

see it adds extra single quotes and command fails.

anybody please help, i hope its very easy.

i tried using sed and removing single quote from variable but that not the problem as soon as i give here as parameter to tar command it gets converted same.

Can you not make the variable not contain --exclude

tar -cvf /tmp/temp.tar --exclude "$patern" dir

thanks , i have solved it by using "awk" with help of some other shell programmer.