arithmetic

Arithmetic in Bash

Integer Arithmetic

There 3 ways to do integer arithmetic in bash:

• Declare an integer variable or expression using let.
• Declare an integer variable or expression using declare.
• Enclose an integer variable or expression using double parenthesis.

According to ShellCheck, prefer (( expr )) instead of let expr.

Let

Using let.

let a=1+2
echo $a   # Prints 3
let "a = 1 + 2"
echo $a   # Prints 3
let a=$a+3
echo $a   # Prints 6
let a++
echo $a   # Prints 7
let a=$a**2
echo $a   # Prints 49

See source code

Declare

Using declare.

a=1+2
echo $a   # Prints 1+2
declare -i a
a=1+2
echo $a   # Prints 3

See source code

Double Parenthesis

Using double parenthesis.

a=$((1+2))
echo $a   # Prints 3
a=$(( 1 + 2))
echo $a   # Prints 3
a=$((a+3))
echo $a   # Prints 6
((a++))
echo $a   # Prints 7
a=$((a**2))
echo $a   # Prints 49

See source code

Float Arithmetic

For floating point calculation in bash use bc.

a=$((1+2.5))
echo $a   # Gives an error (error token is ".5")
a=$(echo "1+2.5" | bc)
echo $a   # Prints 3.5
a=$(echo "$a+0.5" | bc)
echo $a   # Prints 4.0

See source code