# Bash - Arithmetic Expression (())

### Table of Contents

## About

arithmetic in bash

part of compound expression .

## Syntax

```
(( arithmetic expression ))
# or to capture the output
$((arithmetic_expression))
# or
let arithmetic_expression [arithmetic_expression, ...]
```

where let is the let command

If the value of the expression is:

- non-zero, the return status is 0;
- otherwise the return status is 1.

## Management

### Variable

If the variable has its integer attribute set (see Bash - Declare (Variable declaration and attribute)), then value is evaluated as an arithmetic expression even if the $((...)) expansion is not used.

### Operator

In the context where an assignment statement is assigning a value to a shell variable, the += operator can be used to append to or add to the variable’s previous value. When += is applied to a variable for which the integer attribute has been set, value is evaluated as an arithmetic expression and added to the variable’s current value, which is also evaluated.

### Comparison

- As number

```
if (( a > b )); then
...
fi
```

- As string in a conditional expression.

```
if [ "$a" -gt "$b" ]; then
...
fi
```