Yeah. The only one you really need to care about (especially under Linux) is PCRE, the good 'ol Perl Compatible Regular Expressions. For the most part, every other flavor is a derivative of that. Microsoft had a weird version for a while, but that may be completely dead now, thankfully.
Learning the syntax of regex is fairly easy. Hell, I still have to use this cheat sheet more often now that my perl skills are no longer needed or even relevant.
Regex isn’t that hard. The challenge is identifying and understanding patterns in the data that you are filtering. Here is a brain hack: As an example, if to have pages and pages of logs that you need to filter, open up one of the log files, stare at the screen and hold the page down key for several dozen pages. Patterns can be easily seen in the blur of text that is quickly scrolling across the screen. (Our brains love to find patterns in noise, btw.) The patterns that you see will give you focus points for developing regular expressions to match. ie: You start breaking strings into chunks and seeing the ebb and flow of data streaming across a screen helps. Anomalies in the data “stream” are are easy to spot as well.
From a security and efficiency standpoint, you should also understand where the most processing takes place so you don’t kill whatever platform you are working on.
Sorry for the rambling, but I am getting older and feel the need to pass on a ton of tips and tricks whenever I can for these “archaic” languages.