Replacebot

Regular expressions are learned by trying them on real text, and this bot, titled Replacebot in Telegram, is built around a personal set of them. Its description says it reformats data with regular expressions, and its command menu shows how the set is managed: /add saves a new expression, /modify changes one, /list shows everything you have saved and /remove deletes one. /cancel stops the current step, /deleteaccount deletes your user record, and /help explains the exact input format.

Keeping expressions is the useful part when you are learning. Instead of retyping a pattern every time, you build a small library of transformations and reuse them on new samples.

Two warnings. Nobody is named as the author and there is no website or repository, so whatever you send goes to a server run by someone unknown; use sample text, not real data. And an automated check by a third-party bot catalogue recorded that the bot did not reply within a minute, with no date shown, so it may not be running. If /start gets no answer, a regex tester in the browser does the same job.