bash-defensive-patterns

# Bash Defensive Patterns Comprehensive guidance for writing production-ready Bash scripts using defensive programming techniques, error handling, and safety best practices to prevent common pitfalls and ensure reliability. ## When to Use This Skill - Writing production automation scripts - Building CI/CD pipeline scripts - Creating system administration utilities - Developing error-resilient deployment automation - Writing scripts that must handle edge cases safely - Building maintainable shell script libraries - Implementing comprehensive logging and monitoring - Creating scripts that must work across different platforms ## Core Defensive Principles ### 1. Strict Mode Enable bash strict mode at the start of every script to catch errors early. ```bash #!/bin/bash set -Eeuo pipefail # Exit on error, unset variables, pipe failures ``` **Key flags:** - `set -E`: Inherit ERR trap in functions - `set -e`: Exit on any error (command returns non-zero) - `set -u`: Exit on undefined variable reference - `set -o pipefail`: Pipe fails if any command fails (not just last) ### 2. Error Trapping and Cleanup Implement proper cleanup on script exit or error. ```bash #!/bin/bash set -Eeuo pipefail trap 'echo "Error on line $LINENO"' ERR trap 'echo "Cleaning up..."; rm -rf "$TMPDIR"' EXIT TMPDIR=$(mktemp -d) # Script code here ``` ### 3. Variable Safety Always quote variables to prevent word splitting and globbing issues. ```bash # Wrong - unsafe cp $source $dest # Correct ...