Filter for regular expression of "\d" does not work, but "[0-9]" does work.
Filtering regexps are POSIX Extended¹, not Perl². Use "[:digit:]" if you want to match a digit. ¹ http://man7.org/linux/man-pages/man7/regex.7.html ² https://perldoc.perl.org/perlre.html
Thanks!