Begin by setting up your Google Cloud SDK on your local machine or server. Authenticate with your Google Cloud account using the command `gcloud auth login`. Then, create a Pub/Sub topic where your data will be published by running `gcloud pubsub topics create YOUR_TOPIC_NAME`.

Use Snowflake's `COPY INTO` command to export data to a staging area, such as an S3 bucket or an Azure Blob Storage container. For example, use:
```sql
COPY INTO 's3://your-bucket-name/data/'
FROM your_table
FILE_FORMAT = (TYPE = 'CSV');
```
Ensure you have the necessary permissions and credentials configured for Snowflake to access the storage service.

Once the data is exported to the external storage, download it to your local system using the storage service's CLI tools (like AWS CLI for S3). For example:
```bash
aws s3 cp s3://your-bucket-name/data/ ./local-directory/
```

Transform the downloaded data into a format suitable for Pub/Sub. Ensure that each message conforms to Pub/Sub's message size limits and structure. You might need to split large data files into smaller chunks or format them as JSON strings.

Install the Google Cloud Pub/Sub client library for your preferred programming language. For Python, use:
```bash
pip install google-cloud-pubsub
```

Write a script using the Pub/Sub client library to read the transformed data files and publish them to your Pub/Sub topic. For Python, an example script would look like:
```python
from google.cloud import pubsub_v1

def publish_messages(project_id, topic_id, data_file):
publisher = pubsub_v1.PublisherClient()
topic_path = publisher.topic_path(project_id, topic_id)

with open(data_file, 'r') as file:
for line in file:
data = line.encode('utf-8')
future = publisher.publish(topic_path, data)
print(f'Published message ID {future.result()}')

publish_messages('your-project-id', 'YOUR_TOPIC_NAME', './local-directory/data.csv')
```

To ensure the data has been successfully delivered, use the Google Cloud Console to monitor your Pub/Sub topic and check if the messages were received. You can also set up a subscriber to pull messages from the topic and validate the data.

By following these steps, you can move data from Snowflake to Google Pub/Sub without relying on third-party connectors or integrations. Adjust the steps as needed based on your specific requirements and environment configurations.