Shell Arithmetic using expr

• shell treats all shell variables as strings.
• shell uses the expr command  to  perform integer arithmetic.
• expr command cannot do real or non-integer arithmetic.
• expr takes two integer arguments and an operand and writes the result to the standard output. If the output need to be stored in a variable, command substitution(`) need to be used.

$ expr 1 + 1

2

$ a=`expr 1 + 1`

$ echo $a

2

There must be spaces between the operand and the arguments.

Note: * is the multiplication operand. But * has special meaning to the shell. Hence while using *, it should be shielded using \ character.

$ expr 2 \* 2

4