Regex pattern to validate email addresses

When you have many changes, and you want to spread them across different commits, here is a way to stage all changes matching a given regular expression for a single commit.

Example

Consider the following git diff output.

diff --gi...

The way MySQL's FULLTEXT tokenizer splits text into word tokens might not always be what you need. E.g. it splits a word at period characters.

Since the tokenizer has near-zero configuration options (minimum word length and stopwords list), you n...

When you repeat a subpattern with a *, + or {...} operator, you may choose between greedy, lazy and possessive modes.

Switching modes may affect the result and performance of your regular expressions. In the worst case, an ill-s...

The Truemail gem (not to be confused with truemail.io) allows validating email addresses, e.g. when users enter them into a sign-up form. It runs inside your application and does not depend on an external...

There is a practical short list for valid/invalid example email addresses - Thanks to Florian L.! The definition for valid emails (RFC 5322) [can be unhandy for some reasons](https://www.what...

The following two hints are taken from Github's Ruby style guide:

If your regular expression mentions a lot of forward slashes, you can use the alternative delimiters %r(...), %r[...] or %r{...} instead...

For Email-Patterns see most recent E-Mail-Pattern.

HOST = /\A[a-z0-9]+[a-z0-9\-\.]*[a-z0-9]+\z/i
BANK_CODE = /\A\d{8}\z/                                          # Germany
BANK_ACCOUNT_NUMBER = /\A\d...