---
title: Avoid deprecated $[expr] arithmetic expansion syntax
description: Datadog, the leading service for cloud-scale monitoring.
breadcrumbs: >-
  Docs > Datadog Security > Code Security > Static Code Analysis (SAST) > SAST
  Rules > Avoid deprecated $[expr] arithmetic expansion syntax
---

# Avoid deprecated $[expr] arithmetic expansion syntax

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## Metadata{% #metadata %}

**ID:** `bash-code-quality/deprecated-bracket-arithmetic`

**Language:** Bash

**Severity:** Warning

**Category:** Code Style

## Description{% #description %}

The `$[expression]` form is an old Bash arithmetic expansion. It was never documented in POSIX, and Bash 5.2 removed support for it without a clear parse error in all cases, so scripts can fail silently on newer systems.

Use the standard `$((expression))` form instead, which is widely supported and portable.

## Non-Compliant Code Examples{% #non-compliant-code-examples %}

```bash
#!/bin/bash
echo "$[1 + 1]"
y=$[2 * 3]
```

## Compliant Code Examples{% #compliant-code-examples %}

```bash
#!/bin/bash
echo "$((1 + 1))"
x=$((a * 2))
y=$(( (3 + 4) ))
```
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