server/debian/mariadb-server-10.x.mysql-server.logrotate
line 14: if [ -f `my_print_defaults --mysqld | grep -oP "pid-file=\K[^$]+"` ]; then

this always fails in GNU grep v. 22.4 because of:

_*$ echo $ | grep -Pz $
grep: unescaped $ or $ not supported with -Pz
...
This is desired behavior of GNU grep version 2.24 (released on March 10 2016) and above, and that's the fix for the bug which was introduced in GNU grep 2.5.
...
*_
https://unix.stackexchange.com/questions/324263/grep-command-doesnt-support-start-and-end-of-line-anchors-when-its-wit

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=22655#47

Though it's a GNU grep issue there's the need for adjusting grep condition to circumstances.