idempotent-shell-scripts

name	idempotent-shell-scripts
description	Create re-runnable infrastructure shell scripts for gcloud and bq that safely handle existing resources and produce deterministic outcomes across repeated executions.
metadata	{"author":"benthepsychologist","version":"1.0"}
compatibility	Requires bash with set -euo pipefail, authenticated gcloud CLI, and bq CLI in PATH.
allowed-tools	bash gcloud bq

Idempotent Shell Scripts

Use this skill for bootstrap/provision scripts that must be safe to run many times.

Script baseline

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

PROJECT_ID="${PROJECT_ID:?PROJECT_ID is required}"
DATASET="${DATASET:-analytics}"

if ! bq --project_id "$PROJECT_ID" show --dataset "$DATASET" >/dev/null 2>&1; then
  bq --project_id "$PROJECT_ID" mk --dataset "$DATASET"
fi

Patterns to apply

• Check-before-create for all resources.
• Prefer update/apply operations over delete/recreate.
• Gate destructive operations behind explicit flags.
• Validate required env vars at script start.

Verification

bash scripts/bootstrap.sh
bash scripts/bootstrap.sh

Second run must succeed without duplicating resources.