Re: Bug#467378: coreutils: Please include a program to truncate files

[Pádraig Brady]

Jim Meyering wrote:
> Paul Eggert <address@hidden> wrote:
>> Jim Meyering <address@hidden> writes:
>>> If you don't mind truncating first, how about this?
>>>
>>>     true > /var/spool/whatever/foo
>>>     dd bs=1 seek=2G of=/var/spool/whatever/foo < /dev/null
>> Also, the latter command works even if the former command is omitted.
>> That is, by itself, that invocation of dd resizes
>> /var/spool/whatever/foo to 2 GiB, discarding or extending the file as
>> needed, which is what the original request asked for.
> 
> Hi Paul,
> 
> That depends on your definition of "works".
> If you don't mind retaining the first 2GiB of content in
> a preexisting output file, then it works fine.  But the initial
> truncation is required if you want to be sure it's a big sparse
> file with nothing but NUL bytes.
> 
> Try this:
> 
>     echo foo > k
>     dd bs=1 seek=2G of=k < /dev/null
>     head -c4 k
> 
> and note that it prints "foo\n".

That's how I would expect it to work,
and is how I'm currently implementing it.
Given the name "truncate" I think this
operation should be obvious to users.

Pádraig.

p.s. I'm going to push the "timeout" and "truncate"
utils to util-linux-ng/misc-utils/  via Karel Zak
within the next couple of days.