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Sync a folder on server with bucket
s3cmd sync /this/www/ s3://to/this/bucket/

Copy one bucket to another
s3cmd sync s3://from/this/bucket/ s3://to/this/bucket/

http://s3tools.org/download
http://tecadmin.net/install-s3cmd-manage-amazon-s3-buckets/
http://tecadmin.net/s3cmd-file-sync-with-s3bucket/

Human readable size on s3cmd
s3cmd du -H s3://my-bucket