Re: bash sockets: printf \x0a does TCP fragmentation

From	Chet Ramey <chet.ramey@case.edu>
Newsgroups	gnu.bash.bug
Subject	Re: bash sockets: printf \x0a does TCP fragmentation
Date	2018-09-23 14:23 -0400
Organization	ITS, Case Western Reserve University
Message-ID	<mailman.1179.1537727003.1284.bug-bash@gnu.org> (permalink)
References	<c6de6616-dda0-570d-de56-419e7676be8a@cbii-hh.de> <69b48113-bc58-e0c8-a551-03a7e72d88d4@case.edu> <1a70754f-4302-1c96-1ae3-5ab9bdbdf8c3@iki.fi> <0e5b46b7-a1cc-7f0f-e022-38fd19df2a22@testssl.sh>

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On 9/22/18 6:49 AM, dirk+bash@testssl.sh wrote:
> 
> 
> On 9/22/18 12:38 PM, Ilkka Virta wrote:
>> On 22.9. 02:34, Chet Ramey wrote:
>>> Newline? It's probably that stdout is line-buffered and the newline causes
>>> a flush, which results in a write(2).
>>
>> Mostly out of curiosity, what kind of buffering logic does Bash (or the builtin
>> printf in particular) use? It doesn't seem to be the usual stdio logic where you get
>> line-buffering if printing to a terminal and block buffering otherwise. I get a
>> distinct write per line even if the stdout of Bash itself is redirected to say
>> /dev/null or a pipe:
>>
>>  $ strace -etrace=write bash -c 'printf "foo\nbar\n"' > /dev/null
>>  write(1, "foo\n", 4)                    = 4
>>  write(1, "bar\n", 4)                    = 4
>>  +++ exited with 0 +++
> 
> Oh. But thanks anyway!
> 
> coreutils in fact does it in one shot as you indicated.

Then the change you need suggests itself:

env printf ...

or

(exec printf ...)

since the bash exec builtin doesn't execute builtin commands.

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

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Re: bash sockets: printf \x0a does TCP fragmentation Chet Ramey <chet.ramey@case.edu> - 2018-09-23 14:23 -0400

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