Bash Error Handling: How to Use set -o errtrace for Reliable Scripts

Understanding set -o errtrace in Bash: Error Handling in Functions and Subshells

When writing reliable and maintainable Bash scripts, especially for automation and DevOps tasks, handling errors effectively is crucial. One underused but powerful Bash option is set -o errtrace, or its shorthand set -E.

In this article, we’ll explore what errtrace does, why it's important, and how to use it to make your shell scripts more robust.

#Bash Error Hling: How Use set -o errtrace for Reliable Scripts

Problem: `trap ERR` Doesn't Work in Functions by Default

You may know that you can trap errors using:

trap 'echo "An error occurred!"' ERR

But did you know that this trap does not work inside functions or subshells by default?

❌ Example:

trap 'echo "Something went wrong!"' ERR

failing_function() {
  false  # This command fails
}

failing_function

Expected Output:

Something went wrong!

Actual Output:
(No output — the trap is ignored in the function)

✅ Solution: Use `set -o errtrace` or `set -E`

To inherit the ERR trap into functions and subshells, use:

set -o errtrace
# or the shorthand:
set -E

✅ Corrected Example:

set -E
trap 'echo "Something went wrong!"' ERR

failing_function() {
  false
}

failing_function

Output:

Something went wrong!

Now the trap works even inside the function!

🔐 Combine with Safe Scripting Practices

To write safe and predictable scripts, combine the following:

set -eEuo pipefail
trap 'echo "Error occurred at line $LINENO"' ERR

set -e: Exit script on any error
set -u: Treat unset variables as errors
set -o pipefail: Catch errors in piped commands
set -E: Inherit ERR traps in functions/subshells

Real-world Use Case

Imagine you’re writing a deployment script:

set -eEuo pipefail
trap 'echo "Deployment failed at line $LINENO"' ERR

deploy() {
  echo "Starting deployment..."
  false  # Simulating a failure
  echo "Deployment finished"
}

deploy

Without set -E, the trap wouldn’t run. With it, the error is properly logged and caught.

Conclusion

Using set -o errtrace (or set -E) in your Bash scripts ensures consistent error trapping behavior across functions and subshells. This small addition can make your scripts much more reliable, especially in production or automation pipelines.

🔧 Tip: Always test your trap and error handling logic — one small flag can change everything!