First, ensure you have access to your commercetools project. Generate API credentials by setting up a new API client in the commercetools Merchant Center. Take note of the client ID, client secret, project key, and API URL, as you will need them to authenticate and make requests to the commercetools API.

Install and set up a Redis server if you haven't already. You can do this by downloading Redis from the official website and following the installation instructions specific to your operating system. Once installed, ensure the Redis server is running and accessible. You can use the Redis CLI to verify the connection by running commands like `PING`.

Write a script in your preferred programming language (e.g., Python, Node.js) to authenticate and fetch data from commercetools. Use libraries like `requests` in Python or `axios` in Node.js to make HTTP requests. Authenticate using the OAuth 2.0 protocol and use the commercetools API endpoints to retrieve the data you need, such as products, categories, or orders.

Once the data is fetched, parse the JSON response to extract the relevant information. Depending on your use case, you may need to transform or filter the data to fit the structure you want to store in Redis. This might involve converting data types, flattening nested structures, or extracting specific fields.

Determine the appropriate Redis data structure for storing your data. Depending on your requirements, you could use strings, hashes, lists, sets, or sorted sets. For example, you might use hashes to store product attributes or lists to maintain ordered sequences of items.

Use a Redis client library in your script to connect to your Redis server and insert the data. For Python, you might use `redis-py`, and for Node.js, you could use `ioredis`. Iterate over the transformed data and use the appropriate Redis commands to store each item. For example, use `HSET` for hashes or `LPUSH` for lists.

After the data is inserted into Redis, perform verification to ensure data integrity. Use the Redis CLI or your client library to retrieve and check the data against the original source from commercetools. Confirm that all expected data is present and correctly formatted. This step helps ensure the migration was successful and that your Redis database is accurate and reliable.

By following these steps, you can effectively move data from commercetools to Redis using custom scripts without relying on third-party connectors or integrations.