Re: possible bug - output stream handling inconsistency in dd

[Paul Eggert]

"Theodoros V. Kalamatianos" <address@hidden> writes:

> lseek is valid on e.g. /dev/hda and people
> would not expect dd to null their data till it reached the desired
> offset.

True.  I guess the algorithm should be to use lseek if possible, and
to write nulls otherwise.  Then ftruncate if possible.

> Perhaps dd should output null bytes only on FIFOs ?

I'd say it should output nulls if lseek fails for any reason.

> On a relative matter, what should dd do in the following case:
>
> $ echo -n AB > f
> $ echo -n ab | dd bs=1 seek=1 >> f
>
> What should the contents of `f' be ?

Just "ABab".  That's a tricky one, since the ">>f" means that stdout
is in append mode, which means all writes are appended to the end of
the file regardless of the current seek position.  So the "seek=1" is
ineffective.