btrfs-snapshot: Take and rotate snapshots on a btrfs file system

  Usage:
  btrfs-snapshot source target snap_name count [-q]
 
  source:    path to make snapshot of
  target:    snapshot directory
  snap_name: Base name for snapshots, to be appended to 
             date "+%F--%H-%M-%S"
  count:     Number of snapshots in the timestamp-@snap_name format to
             keep at one time for a given snap_name. 
  [-q]:      Be quiet.

Example for crontab:
15,30,45  * * * *   root    /usr/local/bin/btrfs-snapshot / /.btrfs quarterly 4 -q
0         * * * *   root    /usr/local/bin/btrfs-snapshot / /.btrfs hourly 8 -q

Example for anacrontab:
1             10      daily_snap      /usr/local/bin/btrfs-snapshot / /.btrfs daily 8
7             30      weekly_snap     /usr/local/bin/btrfs-snapshot / /.btrfs weekly 5
@monthly      90      monthly_snap    /usr/local/bin/btrfs-snapshot / /.btrfs monthly 3


FAQ:

1. I get an error like "btrfs subvolume snapshot SOURCE DESTINATION: line 77: btrfs: command not found"
Please make sure the btrfs command is in your PATH (e.g. in Debian it is not in cron's default PATH)