You can also configure the CLI via the use of environment variables:

export AWS_PROFILE=<profile-name>

While you should prefer to use profiles over setting your access ID and secret keys directly, sometimes you may have to do so. If you must set your keys directly, do so via environment variables so that you don't need to pass your keys around or hardcode them:

export AWS_ACCESS_KEY_ID=<access-key-id>
export AWS_SECRET_ACCESS_KEY=<secret-access-key>