This example grants full control to two AWS users ([email protected] and [email protected]) and read permission to everyone:

aws s3api put-bucket-acl --bucket MyBucket --grant-full-control 'emailaddress="[email protected]",emailaddress="[email protected]"' --grant-read 'uri="http://acs.amazonaws.com/groups/global/AllUsers"'

See http://docs.aws.amazon.com/AmazonS3/latest/API/RESTBucketPUTacl.html for details on custom ACLs (the s3api ACL commands, such as put-bucket-acl, use the same shorthand argument notation).