Re: Clogged pipe?

On Tue, Apr 04, 2023 at 12:25:36AM -0700, Pete wrote:
> Matthias Apitz wrote on 4/3/23 22:36:
> 
> Well, I was just showing a simplified example to illustrate the problem;
> what I was really trying to script is this:
> 
> /usr/bin/tail -f -n+1 /var/log/exim/main-$(/bin/date -u '+%Y%m%d').log |
> /bin/cat -n |
> /usr/bin/sed -Eu 's/^[[:blank:]]*([[:digit:]]*)[[:blank:]]+/\1 /'
> 
> which prefixes line numbers as it watches today's exim log file scroll
> along. So, in this case the -f flag is needed on the tail command.
> 
> What actually fixes the buffering problem on FreeBSD (it already works fine
> on Linux) is to add the -u flag to the cat command.
> 
> 

Jan Schaumann had a great blog post on pipes buffer sizes a while back
that may be interesting:
https://www.netmeister.org/blog/ipcbufs.html

It dives into the internals and does a pretty great break down of how
various OS's handle buffering.

-pete

-- 
Pete Wright
pete@nomadlogic.org