Bug#984917: feedgnuplot: dynamic plots (--stream) do not work

[Detlev Zundel]

Package: feedgnuplot
Version: 1.57-1
Severity: important
Tags: upstream

I cannot get dynamic plots to work on my system.  To rule out a user error on
my end,
I quickly limited myself to the example from the manpage (adjusted to my
network interface enp6s0):


while true; do sleep 1; cat /proc/net/dev; done |
 gawk '/enp6s0/ {if(b) {print $2-b; fflush()} b=$2}' |
 feedgnuplot --lines --stream --xlen 10 --ylabel 'Bytes/sec' --xlabel seconds

This opens up a gnuplot window but it is not updating every second as it
should.  The lower left
corner seems to be showing a coordinate and this indeed updates every second,
but the plot itself
does not.  From time to time the plot gets redrawn but then again stays fixed.

In order to get more information on the possible culprit, I checked this script
on Ubuntu 18.04 and Debian Buster and on both systems it works fine.  Of course
the gnuplot and feedgnuplot versions are different.

I also cloned feedgnuplot from git without any effect, but sure enough the
Bullseye package is only a single commit behind git main and that commit is a
documentation change.

Doing more diagnosing, I used the --dump switch to see what is being fed into
gnuplot and when I manually run gnuplot and paste the fragments into it, it
works just fine. It seems to be related with the fact that gnuplot reads the
input from the pipe.

Maybe this is related to the gnuplot version in Bullseye?

Thanks in advance
  Detlev

-- System Information:
Debian Release: bullseye/sid
  APT prefers testing
  APT policy: (500, 'testing'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.10.0-3-amd64 (SMP w/8 CPU threads)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages feedgnuplot depends on:
ii  gnuplot-x11 [gnuplot-nox]  5.4.1+dfsg1-1
ii  liblist-moreutils-perl     0.430-2
ii  perl                       5.32.1-3

feedgnuplot recommends no packages.

Versions of packages feedgnuplot suggests:
pn  vnlog  <none>