I've been playing with regex, reading forums and trying out various code on regex101.
In Pi-hole I currently have the following blacklist entry (just one example of many)
^(meetings|hangouts|suggestqueries).*google(apis)?\.com$
I hadn't appreciated until now that this creates two capture groups. Since I don't need these I can modify it to use non-capture groups with the ?: modifier inside the brackets
^(?:meetings|hangouts|suggestqueries).*google(?:apis)?\.com$
I've been testing how Pi-hole handles such groups and modifiers and it appears to respect them all perfectly. If I have two capture groups I can reference them with \1 and \2. If I tweak the first group to be non-capturing with ?: Pi-hole correctly now sees just one group (what was the second one) and references it now as \1. I've been testing with
pihole-FTL regex-test testdomainhere
The bracket syntax in the example above is quite common in here for matching variations of a domain and back-references aren't needed in these cases. So I am inclined to use non-capturing groups, and I've read a few articles where this seems to be considered best practice (non-storing so speeds things up, etc).
However I cannot find any info on Pi-hole's treatment of these or use of the ?: syntax. I assume it handles it correctly because testing seems to show that. The docs suggest that the FTL engine may not quite match what I would see on regex101.
Just wanted to get some feedback on the regex engine's behaviour and any gotchas or anything else worth knowing, before I go ahead and redo a whole raft of expressions on a couple of Pi-holes, adding in the ?: syntax. What about going forward for new expressions? Still worth adding up front?
I'm on latest FTL v5.21. I have read the posts in the regex engine thread but posted a new topic rather than disturb a lot of people by resurrecting the 2-year old thread.