# 正则表达式

- `.` means “any single character” except newline
- `*` zero or more of the preceding match
- `+` one or more of the preceding match
- `[abc]` any one character of `a`, `b`, and `c`
- `(RX1|RX2)` either something that matches `RX1` or `RX2`
- `^` the start of the line
- `$` the end of the line

## 实用工具/参考资料

- https://ihateregex.io/
- https://regex101.com/
- https://www.regular-expressions.info/
- https://emailregex.com/