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Re: bash sockets: printf \x0a does TCP fragmentation


From: Ilkka Virta
Subject: Re: bash sockets: printf \x0a does TCP fragmentation
Date: Sat, 22 Sep 2018 13:38:06 +0300
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

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 +++


--
Ilkka Virta / address@hidden



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