bash-shell-scripting

Bash & Shell Scripting

Core Principles

• DRY: Don't Repeat Yourself
• KISS: Keep It Simple
• Fail Fast: Exit on errors immediately
• Zero Warnings: Must pass shellcheck

Quick Reference

set -euo pipefail           # Strict mode (fail-fast)
set -uo pipefail            # Controlled mode (explicit error handling)
set -Euo pipefail           # Strict + ERR trap propagation
command -v cmd >/dev/null   # Check if command exists (portable)
trap 'cleanup' EXIT         # Always cleanup
flock -n 200 || exit 1      # Prevent concurrent runs
readonly VAR="value"        # Immutable constant
local var="value"           # Function-local variable

Core Standards

Aspect	Standard
Shebang	#!/usr/bin/env bash or #!/bin/bash
Safety Mode	set -euo pipefail (strict) or set -uo pipefail (controlled)
Linting	Must pass shellcheck with 0 errors/warnings
Formatting	Must pass shfmt -i 2 -ci -sr -bn
Extension	.sh for scripts

Error Handling Modes

Strict Mode (Fail-Fast)

set -euo pipefail  # Exit immediately on any error

Use for: Simple linear scripts, dependency installation, straightforward validation.

Controlled Mode (Explicit)

set -uo pipefail  # No -e: handle errors explicitly

Use for: Diagnostics, cleanup operations, commands where failure is expected.

Strict + ERR Trap

set -Euo pipefail

trap 'echo "ERROR in ${FUNCNAME[0]:-main} at line $LINENO"' ERR

Use for: Production scripts with comprehensive error handling.

Script Template

#!/usr/bin/env bash
set -euo pipefail

readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly SCRIPT_NAME="$(basename "$0")"

cleanup() {
    rm -f "${TEMP_FILE:-}" 2>/dev/null || true
}
trap cleanup EXIT

log() {
    echo "[$(date +'%Y-%m-%d %H:%M:%S')] $*" >&2
}

die() {
    log "ERROR: $*"
    exit 1
}

main() {
    local arg="${1:-}"
    [[ -z "$arg" ]] && die "Usage: $SCRIPT_NAME <argument>"
    
    log "Processing: $arg"
    # Main logic here
}

main "$@"