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Re: bash sockets: printf \x0a does TCP fragmentation


From: dirk+bash
Subject: Re: bash sockets: printf \x0a does TCP fragmentation
Date: Sat, 22 Sep 2018 12:49:57 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0


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.


Dirk





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