Feature request: "df -c" - Totals at the base of each collumn

[cragos]

With the GNU implementation of df, it'd be really, really nice to be
able to see a total amount of free diskspace.

/dev/hdb1              70G   54G   17G  77% /mnt/hdb1
/dev/hdb2              70G   63G  7.5G  90% /mnt/hdb2
/dev/hdb3              95G   91G  3.2G  97% /mnt/hdb3
TOTAL                 235G 208G   28G  83%

Yes, this could be scripted.  Yes, there are potential drawbacks, such
as the inclusion of loopback devices, ie:
none                  252M     0  252M   0% /dev/shm

But I believe it should, and quite easily could, be included in df
proper.  It seems like a fairly simple feature to implement.  You
don't even have to do OS-specific checks for loopback devices, if you
just include text like this in the man page:

      -c, --total
             Print a total of each output column.   This can be used
to find out the
             total amount of available, used, and free diskspace
mounted on a system.
             Explicitly specify real devices to avoid double-counting
loopback devices.

Thanks,
Sean Crago