Re: dd skip bug?

[Jim Meyering]

Pádraig Brady <address@hidden> wrote:
> dd handles skip weirdly
>
> disk=/dev/sda8
> dd if=$disk bs=8M count=1 skip=1000 of=/dev/null  #ok
> dd if=$disk bs=8M count=1 skip=1000K of=/dev/null #reads whole disk! as seek 
> fails
>
> I had a 10s look at the source and noticed a comment
> saying POSIX doesn't specify what we should do when
> skipping past the end of input. For seekable files though,
> reading the whole thing is unexpected to me at least.
> I would expect it to do:
>
> if (seekable && !seek(skip_len))
>     exit(EXIT_FAILURE);

Thanks, but the existing behavior is deliberate, and IMHO, necessary.

skip=N is required to try to seek, and failing that, position
the read pointer by calling read.  That is so it works on
e.g., redirected stdin as well as on regular files.

However, as that comment says, an attempt to go
beyond EOF *might* be worth a warning.