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

[Jim Meyering]

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".