What is searched in the deployment process when matching environment variable keys?

In the deployment process, the search for environment variable keys primarily involves the metadata files. These files contain definitions and configurations that are crucial for the deployment environment. When a deployment occurs, the system looks through the metadata files to identify any environment variable keys defined there. This ensures that the correct values are applied during the deployment, allowing for a smooth transition of configurations across different environments.

The other choices do not directly pertain to the matching of environment variable keys in the deployment process. Environment variables themselves act as a storage medium for these values, while custom fields and global settings, though they may contain relevant information, are not the main focus when specifically aligning with the keys in metadata files. Thus, the emphasis on metadata files in this context is essential as they provide the structure and information necessary for the deployment to recognize and utilize the defined environment variables effectively.