56 lines
1.7 KiB
Markdown
56 lines
1.7 KiB
Markdown
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# Regular expression
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Read [Syntax](https://github.com/google/re2/wiki/Syntax).
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Read [Golang-Regex-Tutorial](https://github.com/StefanSchroeder/Golang-Regex-Tutorial).
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Play with [Regex101](https://regex101.com/).
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## Basic
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| regex | meaning |
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| ------------ | ----------------------------------------- |
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| `.` | any character, default not including `\n` |
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| `[xy]` | `x` or `y` character |
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| `[^xy]` | not `x` and `y` character |
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| `x`\|`y` | `x` or `y` |
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| `x*` | 0 or more `x`, prefer **more** |
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| `x+` | 1 or more `x`, prefer **more** |
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| `x?` | 0 or 1 `x` , prefer 1 |
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| `x*?` | 0 or more `x`, prefer **fewer** |
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| `x+?` | 1 or more `x`, prefer **fewer** |
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| `^` | at beginning of text |
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| `$` | at end of text |
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| `\d` | digits |
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| `\D` | not digits |
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| `\s` | whitespace |
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| `\S` | not whitespace |
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| `(foo)` | numbered capturing group (submatch) |
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| `(?:foo)` | non capturing group |
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| `(?:x`\|`y)` | `x` or `y` expression wrap in `()` |
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| `(?flags)` | set flags within current group |
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| flag | meaning |
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| ---- | ---------------- |
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| `i` | case-insensitive |
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| `s` | `.` match `\n` |
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## Example
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```regex
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(?i)hello\sfoo
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match: Hello Foo
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match: heLLo fOO
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```
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```regex
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hello\s(.+)
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match: hello foo
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group 1: foo
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match: hello bar
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group 1: bar
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```
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