Re: piping tail -f through cut

[Micah Cowan]

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Pádraig Brady wrote:
> Bob van Loosen wrote:
>> Hi everyone,
>>
>> Whenever I do this:
>>
>> tail -f  /var/log/kern.log | cut -f 8- -d " " | dd bs=1
>>
>> I get no output, but when I do this:
>>
>> tail -f  /var/log/kern.log | cut -f 8- -d " "
>>
>> I do get output, I'm using coreutils 5.97 on Ubuntu 7.10 64 bit.
> 
> I've documented that exact case here:
> http://www.pixelbeat.org/programming/stdio_buffering/
> 
> There's a patch for `cut` there,
> which demonstrates how to add this functionality to coreutils.
> 
> Personally I think it would be great to add the buffering control
> to glibc, so that most applications would benefit.
> But Ulrich Drepper <sarcasm>in his usual amiable style</sarcasm>
> suggested this was a silly idea.

It is a very silly idea, considering it would violate the C standard
(§7.19.3#7):

As initially opened, the standard error stream is not fully buffered;
the standard input and standard output streams are fully buffered if and
only if the stream can be determined not to refer to an interactive device.

- --
Micah J. Cowan
Programmer, musician, typesetting enthusiast, gamer...
http://micah.cowan.name/
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