If you find yourself using a named profile for every awscli command, you can set it temporarily.

Listing a bucket with a named profile.

aws s3 ls --profile=yourprofile

If you set AWS_PROFILE, you can then list a bucket without a named profile.

export AWS_PROFILE=yourprofile
aws s3 ls

After you are done, you can reset it back to default.

export AWS_PROFILE=default