How do I add and subtract using bash shell script.

shoebill

Adding.

let sum="10 + 1"
echo "10 + 1, That's legs $sum."

Running this script gives:

$ ./addsub.sh
10 + 1, That's legs 11.

In the let statement change + for a minus.

Subtract.

let sum="10 - 1"
echo "10  - 1, That's $sum, Doctor's Orders."

Running this script gives:

$ ./addsub.sh
10 - 1, That's 9, Doctor's Orders.