Arithmetic expansion

With arithmetic expansion we can perform math with integers in our scripts and get the result returned to a variable. Similar to command substitution we can use $(( )) to get the calculated value. If we use brackets alone, (( )), only the calculation is performed. Let us look at the difference.

#Double brackets

First, we look at evaluation:

#!/usr/bin/env bash
#
# An example of arithmetic evaluation

value=4
(( value+=1 ))

echo "$value" # Prints 5

Then we look at expansion:

#!/usr/bin/env bash
#
# An example of arithmetic expansion

value=4
result=$(( value+=1 ))

echo "$result" # Prints 5

#The built-in command let

The built-in command let lets us use mathematical formulas on variables. Similar to (()) it only performs the calculation (arithmetic evaluation).

#!/usr/bin/env bash
#
# An example script for the linux course

# With the keyword "let"
value1=5
value2=10
let value3=$value1+$value2

echo "$value3" # Prints 15

#Revision history