numfmt enhancements to emulate df -g

[Pádraig Brady]

On 05/06/15 17:52, Michael Felt wrote:

> michael@x071:[/usr/bin]/usr/bin/df -g .
> Filesystem    GB blocks      Free %Used    Iused %Iused Mounted on
> /dev/hd2           3.00      0.18   94%    57355    54% /usr

> I guess what I could do is look at creating an alias so that
> a) look to see if df/du is not /usr/bin/df/du - and if so, use df -BG

I see that df -g on AIX gives precision of 2 decimal places.
We should be able to achieve that easily with numfmt.
Also numfmt should more easily process multi field output (from df).
These were already TODO items which I've now implemented in the attached patch 
set.

This would allow you to setup an alias that does:

  $ df -B1 | numfmt --field - --invalid=ignore --to-unit=G --format=%.2f 
--suffix=G
  Filesystem        1B-blocks        Used  Available Use% Mounted on
  devtmpfs              4.13G       0.00G      4.13G   0% /dev
  ...

Dylan I used/adjusted your patch for multiple fields support.
Note I moved from an avltree to a linked list so that memory
consumption was proportional to the number of field specifications,
rather than the number of fields specified.  One could have
done that with a tree also (an interval tree), but that would
have involved deeper integration in the tree insertion routines
to augment the range values.  This would have been a false optimization
though since a better one is to take advantage of the fact we're doing
a linear scan, rather than random lookup, which cut does.
So I added a TODO to refactor the cut implementation
for use by both cut and numfmt.

cheers,
Pádraig.

numfmt-df-g.patch
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