Bash Skill

Best Practices

1. Robustness & Safety

• Always Quote Variables: Use "$var" to prevent word splitting and globbing issues.
• Check Dependencies: Verify required tools (command -v cmd) at the start of the script.
• Use printf over echo: printf is more portable and reliable for formatted output.
• Avoid eval: It is a security risk. Use arrays or functions instead.
• Immutable Variables: Use readonly for constants (e.g., readonly LOG_FILE="/tmp/log").

2. Code Style & Structure

• Shebang: Always use #!/usr/bin/env bash for portability across systems (e.g., macOS vs Linux).
• Naming:
  • UPPER_CASE for exported environment variables and constants.
  • lower_case for local variables and function names.
  • _leading_underscore for private/internal variables.
• Functions: Wrap logic in functions. Use main as the entry point.
• Scope: Always declare function variables with local.

3. Error Handling & Logging

• Structured Logging: Use timestamps and log levels (INFO, WARN, ERROR).
• StdErr: Print logs and interactive messages to stderr (>&2), keeping stdout clean for piping data.
• Traps: Use trap cleanup EXIT to ensure temporary files/locks are removed, even on failure.

4. Input Validation

• Argument Parsing: Use a while loop with case (or getopts) to handle flags clearly.
• Validate Assumptions: Check if files exist, variables are set, and arguments are valid numbers/strings before proceeding.

5. Security

• Secrets: Never hardcode secrets. Read them from environment variables or a secure vault.
• Temp Files: Use mktemp to create secure temporary files with restricted permissions.
• Sudo: Avoid using sudo inside scripts. Check if EUID is 0 if root is required, or let the user invoke the script with sudo.

Common Workflow

1. Initialize: Start with the Enterprise Script Template (see PATTERNS.md).
2. Plan: Define the inputs, outputs, and dependencies.
3. Implement: Write functions for distinct tasks (SRP - Single Responsibility Principle).
4. Verify: Run shellcheck (if available) to catch common pitfalls.
5. Test: Use "dry-run" logic to test without side effects.

Quick Reference

• Check String Empty: [[ -z "$var" ]]
• Check String Not Empty: [[ -n "$var" ]]
• File Exists: [[ -f "$file" ]]
• Dir Exists: [[ -d "$dir" ]]
• Math: (( count++ )) or result=$(( a + b ))
• Arrays: arr=("a" "b"); echo "${arr[0]}"