I know exists, I needed it anyway.
It uses the standard s3cli authentication methods.
s3put --bucket=<bucket> --region=<region> <file> <key>
You can use environment variables to provide secret key & access key:
AWS_SECRET_KET=abc AWS_ACCESS_KEY=def s3put --bucket=<bucket> --region=<region> <file> <key>
Using stdin
s3put --bucket=<bucket> --region=<region> -- - <key>
Uses multipart upload to allow files bigger than 5GB.