Re: du: POSIX mandating a single space instead of tab?

[Pádraig Brady]

On 28/04/15 15:42, Eric Blake wrote:
> On 04/28/2015 03:59 AM, Pádraig Brady wrote:
> 
>>>>     The output from du shall consist of the amount of space allocated
>>>>     to a file and the name of the file, in the following format:
>>>>
>>>>     "%d %s\n", <size>, <pathname>
>>>>
>>>> Instead, GNU du uses "%d\t%s\n", i.e., a tab character as delimiter,
>>>> even if POSIXLY_CORRECT is set.
>>>>
>>>> Do I read POSIX right?
>>>
>>> No, the space stands for any (positive) amount of white space.
>>>
>>> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap05.html#tag_05
>>>
>>> Andreas.
>>>
>>
>> Thanks for pointing that out Andreas.
>> So a ' ' in a format implies any amount of blank chars.
> 
> Correct.
> 
>> So we could separate the du columns with spaces rather than tab,
> 
> Yes, I'd prefer that we did that.  It is much easier to guarantee
> alignment when using spaces and completely avoiding whatever tab stops
> people have set up.
> 
>> though that would almost definitely introduce a compatibility issue,
>> and would be inconsistent with Solaris and FreeBSD at least.
> 
> POSIX is already clear that anyone parsing for literal tabs is broken
> when trying to parse du output.  The only safe way to parse du output is
> to break on all whitespace (the way awk already does).  I'm 70-30 in
> favor of changing to spaces.

What about file names with leading whitespace,
which now couldn't be split if we didn't use a single tab.

I don't think the gain is enough to break compat,
given the greater alignment control etc. possible
with expand(1) or numfmt(1) etc.
I just checked an old wrapper script for du that I use,
and see that it would be broken for example:
http://www.pixelbeat.org/scripts/dutop

cheers,
Pádraig.