I used a program called “Agent Ransack” when I was on Windows.
One very useful feature was being able to search files using regular expressions, e.g. ^PX_.*(cbl|cpy)$
I looked for alternatives for Agent Ransack on Linux, but unfortunately nothing comes close, or they’re just too hard to use, or it’s very outdated software.
kfind seems to be a great tool, and it’s very nice that it’s native, but I’m really missing the regular expression search.
Could a checkbox [x] Regular expression be added to the “Name/Location” and “Contents” tabs? 
Many thanks!