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bash-defensive-patterns

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by wshobson · part of wshobson/agents

Master defensive Bash programming techniques for production-grade scripts. Use when writing robust shell scripts, CI/CD pipelines, or system utilities requiring fault tolerance and safety.

🧩 One of 7 skills in the wshobson/agents package — works on its own, and pairs well with its siblings.

This is the playbook your agent receives when the skill activates — you don't need to read it to use the skill, but it's here to audit before installing.

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

Detailed patterns and worked examples

Detailed pattern documentation lives in references/details.md. Read that file when the navigation tier above is insufficient.

Best Practices Summary

  1. Always use strict mode - set -Eeuo pipefail
  2. Quote all variables - "$variable" prevents word splitting
  3. Use [[]] conditionals - More robust than [ ]
  4. Implement error trapping - Catch and handle errors gracefully
  5. Validate all inputs - Check file existence, permissions, formats
  6. Use functions for reusability - Prefix with meaningful names
  7. Implement structured logging - Include timestamps and levels
  8. Support dry-run mode - Allow users to preview changes
  9. Handle temporary files safely - Use mktemp, cleanup with trap
  10. Design for idempotency - Scripts should be safe to rerun
  11. Document requirements - List dependencies and minimum versions
  12. Test error paths - Ensure error handling works correctly
  13. Use command -v - Safer than which for checking executables
  14. Prefer printf over echo - More predictable across systems