Values can be read from the command line using the read command. See the following code.

read a
read b
echo $a
echo $b

Invoked from the command line:

echo '1\n2'|./read.sh
1
2

To perform an operation, surround the variables with (()) or [] and precede with a $ sign.

read a
read b
echo $[a+b]
echo $((a-b))

Reference Resources
A relevant and interesting discussion on Stack-Exchange for those getting started with handling numbers and arithmetic operations in Bash.

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