Regular Expressions: You are the master of your (massive) text
There are a few apps that provide cheat sheets and expression exercises. Here are a couple of them.
https://play.google.com/store/apps/details?id=com.andkorsh.regexpal&hl=en_US
https://play.google.com/store/apps/details?id=spencerstudios.com.regexapp&hl=en_US