In case it's useful for others, I found "Mastering Regular Expressions" by "Jeffrey E. F. Friedl" to be very effective for becoming proficient with Regex. Also

In case it's useful for others, I found "Mastering Regular Expressions" by "Jeffrey E. F. Friedl" to be very effective for becoming proficient with Regex. Also – reading it was just a useful look into systems mapping (which is what language is!) with insights that apply in many contexts.