Often you may want to convert a string to an integer in Bash to perform some arithmetic operation.

In Bash, it’s important to note that you don’t “convert” a variable from one data type to another.

Rather, variables are simply treated as strings or integers based on the task you’re attempting to perform.

To force a variable to be treated as an integer, you can use the **$((. . .))** operator.

For example, if you want to calculate the sum of two variables named **var1** and **var2** then you can use the following syntax:

**echo $(($var1+$var2))
**

The following example shows how to use this syntax in practice.

**Example: How to Convert String to Integer in Bash**

Suppose that we create two variables in Bash named **var1** and **var2** that both contain integer values.

Suppose we attempt to calculate the sum of these two variables by using a plus ( + ) sign as follows:

**var1=5
var2=10
echo $var1+$var2
**

The following screenshot shows how to use this syntax in practice:

By default, Bash concatenates the two variables together into one string for a result of **5+10**.

To explicitly tell Bash that we would like to treat the variables as integers, we can wrap them in the **$(( . . .))** arithmetic expansion operator as follows:

**var1=5
var2=10
echo $(($var1+$var2))**

The following screenshot shows how to use this syntax in practice:

Notice that Bash now treats the variables as integers and calculates the sum of the two variables to get 5 + 10 = **15**.

Also note that you can drop the **$** symbols inside of the arithmetic expansion operator if you would like:

**var1=5
var2=10
echo $((var1+var2))**

The following screenshot shows how to use this syntax in practice:

Notice that this returns the same result of **15**.

**Note**: In this example we simply added two variables together but you can perform much more complex arithmetic operations within the **$((. . .))** if you would like.

**Related Tutorials**

The following tutorials explain how to perform other common tasks in Bash:

Bash: How to Extract First Number from a String

Bash: How to Check if String Starts with Specific Value

Bash: How to Count Number of Words in String

Bash: How to Count Number of Characters in String