Re: [gentoo-user] Tailing compressed build logs

[Michael]

On Tuesday, 7 March 2023 07:52:01 GMT Mickaël Bucas wrote:
> Le mar. 7 mars 2023 à 05:36, Bryan Gardiner <bog@××××××.net> a écrit :
> > Hi folks,
> >
> > How can I follow Portage's compressed build logs in real time as they
> > are generated?
> >
> > I keep build logs and use FEATURES=compress-build-logs so that they
> > don't get too large.  I can peek at how a build is going with zless on
> > build.log.gz, which doesn't update (understandably), but I would
> > really like to be able to watch a log with some "tail -f" equivalent.
> > I get streaming output with
> >
> >     tail -c +1 -f build.log.gz | od -t x1
> >
> > but the following hangs with no output:
> >     tail -c +1 -f build.log.gz | gunzip
> >
> > even with a build log that is 72KB compressed (2.4MB uncompressed),
> > which should be larger than any pipe buffers...  Any idea why gunzip
> > can't handle this, or what I should I should be doing instead?
> >
> > Thanks,
> > Bryan
>
> Hi
>
> Reading the man page, "zless" is just a wrapper around "less".
> You can check with:
> $ file $(which zless)
> /usr/bin/zless: POSIX shell script, ASCII text executable
> $ less $(which zless)
>
> So it should support the same options including typing "F" at the end
> of a file to keep trying to read when the end of file is reached.
>
> I made a small test, but it didn't work:
> # Create a growing file
> $ yes | nl | gzip > zless-test.gz &
> # Try to follow at the end
> $ zless zless-test.gz
>
> With ">" to go to the end and "F" to continue, I didn't get the
> expected behavior, it stood still at the point I was viewing.
> I don't know if it's really a bug or if I made a mistake...
> (Don't forget to stop the growing file :) )
>
> Best regards
>
> Mickaël Bucas

You could try:

tail -c +1 -f build.log.gz | gunzip | less 

I think it should work, but I haven't tried it.