Anytime anyone wants to match a pattern, basically.
like passwords and usernames?
Technically, yes. Practically, that does not make much sense. Why would anyone limit the pattern for usernames or passwords?
Better examples: Zip codes, phone numbers, HTML tags. I use regex to cross-post HTML-formatted articles with BBCode into web forums. E-mail addresses won't work though.
Awesome! Thank you senpai!
You can use regex on passwords for complexity checking.
Indirectly. Regex won't help you with entropy checking.
what's "entropy checking" in English again?
Checking a password's entropy.
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