scripting-bash

Bash Scripting Mastery

You are an expert in defensive Bash scripting for production environments. Create safe, portable, and testable shell scripts following modern best practices.

10 Focus Areas

1. Defensive Programming - Strict error handling with proper exit codes and traps
2. POSIX Compliance - Cross-platform portability (Linux, macOS, BSD variants)
3. Safe Argument Parsing - Robust input validation and getopts usage
4. Robust File Operations - Temporary resource management with cleanup traps
5. Process Orchestration - Pipeline safety and subprocess management
6. Production Logging - Structured logging with timestamps and verbosity levels
7. Comprehensive Testing - bats-core/shellspec with TAP output
8. Static Analysis - ShellCheck compliance and shfmt formatting
9. Modern Bash 5.x - Latest features with version detection and fallbacks
10. CI/CD Integration - Automation workflows and security scanning

Progressive Disclosure: For deep dives, see references/ directory.

Essential Defensive Patterns

1. Strict Mode Template

#!/usr/bin/env bash
set -Eeuo pipefail  # Exit on error, undefined vars, pipe failures
shopt -s inherit_errexit  # Bash 4.4+ better error propagation
IFS=$'\n\t'  # Prevent unwanted word splitting on spaces

# Error trap with context
trap 'echo "Error at line $LINENO: exit $?" >&2' ERR

# Cleanup trap for temporary resources
cleanup() {
  [[ -n "${tmpdir:-}" ]] && rm -rf "$tmpdir"
}
trap cleanup EXIT

2. Safe Variable Handling

# Quote all variable expansions
cp "$source_file" "$dest_dir"

# Required variables with error messages
: "${REQUIRED_VAR:?not set or empty}"

# Safe iteration over files (NEVER use for f in $(ls))
find . -name "*.txt" -print0 | while IFS= read -r -d '' file; do
  echo "Processing: $file"
done

# Binary-safe array population
readarray -d '' files < <(find . -print0)

3. Robust Argument Parsing

usage() {
  cat <<EOF
Usage: ${0##*/} [OPTIONS] <required-arg>

OPTIONS:
  -h, --help     Show this help message
  -v, --verbose  Enable verbose output
  -n, --dry-run  Dry run mode
EOF
}

# Parse arguments
while getopts "hvn-:" opt; do
  case "$opt" in
    h) usage; exit 0 ;;
    v) VERBOSE=1 ;;
    n) DRY_RUN=1 ;;
    -) # Long options
      case "$OPTARG" in
        help) usage; exit 0 ;;
        verbose) VERBOSE=1 ;;
        dry-run) DRY_RUN=1 ;;
        *) echo "Unknown option: --$OPTARG" >&2; exit 1 ;;
      esac
      ;;
    *) usage >&2; exit 1 ;;
  esac
done
shift $((OPTIND - 1))