Bash: Debugging – Use set -x, -n, and -v to Troubleshoot Scripts

Introduction to Bash Debugging – Master set -x, set -n, and set -v

Debugging is a crucial part of writing reliable Bash scripts. Bash provides built-in options like set -x, set -n, and set -v to help you trace script execution, detect syntax errors, and understand how your script behaves in real-time.

These debugging flags are simple yet powerful tools to make your script development faster, more predictable, and less error-prone.

In this article, you’ll learn:

• What set -x, -n, and -v do in Bash
• How to enable and disable these debugging modes
• Example outputs to see how each works
• Best practices for script debugging

Debugging Flags Overview

You can enable them using either:

set -x     # or
set -n     # or
set -v

Or combine them:

set -xv

To turn them off:

set +x     # disables tracing

🐾 set -x – Trace Command Execution

Shows each command and its arguments as they execute. Great for spotting logic errors.

Example:

#!/bin/bash
set -x

name="Vaibhav"
echo "Hello, $name"

Output:

+ name=Vaibhav
+ echo 'Hello, Vaibhav'
Hello, Vaibhav

Helpful for checking variable expansion and command flow.

set -n – Check Syntax Without Running

Checks for syntax errors without executing any commands.

Example:

#!/bin/bash
set -n

echo "Start script"
echo "Missing quote
echo "Script continues"

Output:

myscript.sh: line 4: unexpected EOF while looking for matching `"'

Commands are not executed—this is a safe dry-run to detect typos.

set -v – Echo Input Lines Before Execution

Displays each line as it is read, before it’s executed. Useful for reviewing script input.

Example:

#!/bin/bash
set -v

echo "First"
echo "Second"

Output:

echo "First"
First
echo "Second"
Second

Helps understand what code the shell is reading, especially with complex logic.

Combine Debugging Options

Use combinations for deeper insights:

set -xv   # Trace execution and input lines

Disable Debugging Mid-Script

set -x
echo "Tracing ON"
set +x
echo "Tracing OFF"

Output:

+ echo 'Tracing ON'
Tracing ON
Tracing OFF

This approach is great for isolated debugging.

Best Practices for Debugging

Summary – Bash Debugging Options

Bash debugging options like set -x, set -n, and set -v are essential for writing reliable and bug-free scripts. Use them wisely to trace execution, check syntax, and view inputs during development.

Key Takeaways:

• set -x shows command execution with expanded variables
• set -n performs a syntax-only dry run
• set -v displays each input line before execution
• Combine or isolate debug sections for targeted analysis

Real-world Uses:

• Troubleshooting conditional logic or loops
• Verifying cron job behavior without execution
• Understanding input flow in complex scripts

FAQ – Bash Debugging Options

Can I combine multiple set flags?
Yes, like set -xv to trace both input and execution.

Does set -n execute the script?
No. It parses the script and checks for syntax errors without running anything.

How do I stop debugging mid-script?
Use set +x or set +v to disable the corresponding mode.

Is set -v useful without set -x?
Yes. It shows what’s being read line-by-line, which helps for flow review.

Should I keep set -x in production scripts?
No. It clutters output and may expose sensitive values. Use only for debugging during development.