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Re: bash sockets: printf \x0a does TCP fragmentation


From: Chet Ramey
Subject: Re: bash sockets: printf \x0a does TCP fragmentation
Date: Sun, 23 Sep 2018 14:23:08 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 9/22/18 6:49 AM, address@hidden 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    address@hidden    http://tiswww.cwru.edu/~chet/



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