Re: ls -l|head seems to look at all files in directory

[Jim Meyering]

Reuben Thomas wrote:

> On Mon, 25 May 2009, Jim Meyering wrote:
>
>> Pádraig Brady wrote:
>>
>>> Reuben Thomas wrote:
>>>> On Mon, 25 May 2009, Jim Meyering wrote:
>>>>
>>>>> To do what he wants you have to know that ls -1U is the only
>>>>> way to get one output entry per readdir call.
>>>>>
>>>>> Reuben, you want to do it like this:
>>>>>
>>>>>  ls -1U|head|xargs ls -l
>>>>
>>>> Thanks for the hint about -1, but this doesn't seem to make any
>>>> difference: I run "ls -1U|head" in a directory with lots of files (about
>>>> 10,000) and it pauses for a minute or so before giving me my ten lines
>>>> of output.
>>>>
>>>> If I run the command again, then of course it runs almost instantly, so
>>>> I'm not sure what use the loops are in the tests you give.
>>>
>>> With the ls on fedora 8 (coreutils 6.9) I see all the
>>> redundant getdents64() calls when using strace on Jim's command above.
>>> With the latest coreutils I do not.
>>
>> Right.  The change that made ls -1U more efficient was after 6.12
>> [v6.12-113-g8d974b0]:
>
> Ah, I'm using 6.10. Thanks for the clarification.

Argh.
I'll try to ask for the version number next time if you try
to reproduce with latest tools and/or report the version number ;-)