Your First Script

#!/usr/bin/env bash
# script-name.sh — one-line description
# Usage: ./script-name.sh [options] <required-arg>

# ===== 1) Strict mode — catch errors early =====
set -Eeuo pipefail
# -E   ensure ERR trap is inherited
# -e   exit on any error
# -u   error on undefined variables
# -o pipefail   a pipeline fails if ANY stage fails (not just the last)

IFS=$'\n\t'    # word-splitting on newline + tab only (no spaces)

# ===== 2) Globals =====
PROG_NAME=$(basename "$0")
SCRIPT_DIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
TMP="$(mktemp -d -t ${PROG_NAME%.sh}.XXXXXX)"

# ===== 3) Cleanup on any exit =====
cleanup() {
  rm -rf "$TMP"
}
trap cleanup EXIT
trap 'echo "ERROR on line $LINENO. cmd: $BASH_COMMAND" >&2' ERR

# ===== 4) Help + usage =====
usage() {
  cat <<USAGE
$PROG_NAME -- import a CSV into orders table

Usage:
  $PROG_NAME [options] <path-to-csv>

Options:
  -d, --dry-run        do not write to the database
  -e, --env <name>     environment (dev|staging|prod) [default: dev]
  -v, --verbose        more output
  -h, --help           this help
USAGE
}

# ===== 5) Defaults + arg parsing =====
DRY_RUN=0
ENV=dev
VERBOSE=0

while [[ $# -gt 0 ]]; do
  case "$1" in
    -d|--dry-run)  DRY_RUN=1; shift ;;
    -e|--env)      ENV="${2:?missing env value}"; shift 2 ;;
    -v|--verbose)  VERBOSE=1; shift ;;
    -h|--help)     usage; exit 0 ;;
    --)            shift; break ;;
    -*)            echo "unknown option: $1" >&2; usage; exit 2 ;;
    *)             break ;;
  esac
done

CSV_PATH="${1:-}"
if [[ -z "$CSV_PATH" ]]; then
  echo "missing CSV path" >&2; usage; exit 2
fi

# ===== 6) Helpers — keep them small and named =====
log() {
  printf '[%s] %s\n' "$(date +'%Y-%m-%dT%H:%M:%S%z')" "$*" >&2
}

debug() {
  (( VERBOSE )) && log "DEBUG: $*"
}

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

require() {
  command -v "$1" >/dev/null 2>&1 || die "need '$1' on PATH"
}

confirm() {
  read -r -p "$1 [y/N] " ans
  [[ "${ans:-N}" =~ ^[Yy]$ ]]
}

# ===== 7) Main work =====
import_csv() {
  local path="$1"
  [[ -f "$path" ]] || die "CSV not found: $path"
  log "importing $path into $ENV"

  debug "using TMP=$TMP"

  if (( DRY_RUN )); then
    log "DRY RUN — would import $(wc -l <"$path") rows"
    return 0
  fi

  # actual work goes here
  while IFS=, read -r id customer total_cents; do
    debug "row id=$id"
    # ... call the DB, etc.
  done < <(tail -n +2 "$path")
}

main() {
  require psql
  require jq

  import_csv "$CSV_PATH"
  log "done."
}

main "$@"

# ===== Patterns to internalise =====
# - set -Eeuo pipefail at the top of EVERY script
# - mktemp -d for any temp dir; clean up in EXIT trap
# - one main() function called at the bottom
# - small named helpers (log, debug, die, require)
# - manual --long-option parsing (avoid getopt) for portability
# - read -r when reading user input (preserve backslashes)
# - quote ALL variables: "$var"
# - use [[ ... ]] over [ ... ]
# - prefer command substitution $(cmd) over backticks
# - use 'local' inside functions for variables

# ===== Pitfalls =====
# - 'set -e' does NOT exit inside subshells in all cases; check explicitly
# - 'pipefail' is essential — without it, 'grep foo | wc' shows 0 even when grep fails
# - Bash arrays are 0-indexed; "${arr[@]}" expands each element quoted
# - Don't 'cd' without checking; use 'cd ... || die'
# - eval is almost always wrong; reach for arrays or here-docs instead

#!/usr/bin/env bash
set -euo pipefail
echo "Hello from a script"