OpenNebula

For example, the output of 'onevm attachdisk -h' is much more useful than the help shown when the required parameters are not given.

$ onevm attachdisk
Command attachdisk requires one parameter to run

Usage:
    attachdisk <vmid>
        Attaches a disk to a running VM

        States: RUNNING
        valid options: file, image, target

$ onevm attachdisk 0
Provide a template file or an image:
    --file  <file>
    --image <image>

$ onevm attachdisk -h
## USAGE
attachdisk <vmid>
        Attaches a disk to a running VM

        States: RUNNING
        valid options: file, image, target

## OPTIONS
     -f, --file file           Selects the template file
     -i, --image id|name       Selects the image
     -t, --target target       Device where the image will be attached
     -v, --verbose             Verbose mode
     -h, --help                Show this message
     -V, --version             Show version and copyright information
     --user name               User name used to connect to OpenNebula
     --password password       Password to authenticate with OpenNebula
     --endpoint endpoint       URL of OpenNebula xmlrpc frontend