Defensive Shell Scripting: set -euo pipefail

Writing bulletproof automation scripts that fail immediately on bugs

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By default, Bash continues executing subsequent commands even if an earlier command crashes or references an unset variable! "Unofficial Bash Strict Mode" enforces immediate failure.

The Unofficial Bash Strict Mode (`set -euo pipefail`)

set -e: Exit immediately if any command exits with a non-zero status.

set -u: Treat unset variables as errors and exit immediately, preventing catastrophic bugs like rm -rf /tmp/$UNSET_DIR from expanding to rm -rf /!

set -o pipefail: Prevents pipeline errors from being masked. The pipeline returns the exit status of the last command to fail.

Production Strict Mode Boilerplate

Try It Yourself »

#!/usr/bin/env bash
# Enforce strict mode for production reliability
set -euo pipefail
IFS=$'\n\t'

echo "Deploying production release..."

BACKUP_DIR="/backups/$(date +%Y%m%d)"
mkdir -p "$BACKUP_DIR"

# If this command fails, the entire script halts immediately!
rsync -avz /var/www/html/ "$BACKUP_DIR/"

echo "Backup verified successfully."

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Test Yourself With Exercise

+15 XP

Why is `set -u` included in strict defensive Bash scripts?

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