# R* Cheatsheet

## Modifiers

| Symbol | Description                   |
|--------|-------------------------------|
| `g`    | Global - search entire string |
| `i`    | Case-insensitive              |
| `m`    | Multiple lines                |
| `s`    | Treat as single line          |
| `x`    | Allow comments & whitespace   |
| `e`    | Evaluate placement            |
| `U`    | Un-greedy patterns by default |

## Escape

| Symbol | Description               |
|--------|---------------------------|
| `?#`   | Comment                   |
| `\ `   | Escape special characters |
| `\Q`   | Begin literal sequence    |
| `\E`   | End literal sequence      |

## Anchors

| Symbol | Description       |
|--------|-------------------|
| `^`    | Start of line     |
| `$`    | End of line       |
| `\A`   | Start of string   |
| `\Z`   | End of string     |
| `\b`   | Word boundary     |
| `\B`   | Not word boundary |
| `\<`   | Start of word     |
| `\>`   | End of word       |

## Characters

| Symbol | POSIX                                | Description                              |
|--------|--------------------------------------|------------------------------------------|
| `\c`   | `[:cntrl:]`                          | Control character                        |
| `\S`   |                                      | Not a white space                        |
| `\s`   | `[:blank:]` `[:space:]`              | White space                              |
|        | `[:punct:]`                          | Punctuation                              |
| `.`    | `[:print:]` `[:graph:]`              | Printed Character, with & without spaces |
| `\W`   |                                      | Not a letter                             |
| `\w`   | `[:alpha:]` `[:upper:]`  `[:lower:]` | Letter                                   |
| `\D`   |                                      | Not a number                             |
| `\d`   | `[:digit:]`                          | Number                                   |
| `\x`   | `[:xdigit:]`                         | Hexadecimal digit                        |
| `\O`   |                                      | Octal digit                              |
| `\n`   |                                      | New line                                 |
| `\r`   |                                      | Carriage return                          |
| `\t`   |                                      | Tab                                      |
| `\v`   |                                      | Vertical tab                             |
| `\f`   |                                      | Form feed                                |
| `\xxx` |                                      | Octal number "xxx"                       |
| `\xaa` |                                      | Hexidecimal "aa"                         |

## Repeat

| Symbol   | Range       | Description                           |
|----------|-------------|---------------------------------------|
|          | `{x}`       | Exactly `x` times                     |
|          | `{min,max}` | Repeat between `min` & `max` times    |
| `?`      | `{,1}`      | 0 or 1                                |
| `*` `*?` | `{0,}`      | 0 or many (Adding `?` make un-greedy) |
| `+` `+?` | `{1,}`      | 1 or more (Adding `?` make un-greedy) |

Un-greedy repeaters will take the minimum number of characters required

## Group Selectors

| Symbol         | Description                                |
|----------------|--------------------------------------------|
| `.`            | Wildcard/Single character (Except newline) |
| `(abc\|123)`   | `abc` or `123`                             |
| `(...)`        | Capture group                              |
| `(?<name>...)` | Named capture group                        |
| `(?:...)`      | Group un-captured                          |
| `[abc]`        | `A` or `B` or `C`                          |
| `[^abc]`       | Not `A` or `B` or `C`                      |
| `[0-9]`        | Number between `0` and `9`                 |
| `[a-g]`        | Lowercase letter between `a` and `g`       |
| `[A-G]`        | Uppercase letter between `A` and `G`       |

All selectors are inclusive

## Reference Group

| Symbol  | Description    |
|---------|----------------|
| `$n`    | N'th Group     |
| `$\` ` | Before matched |
| `$'`    | After matched  |
| `$+`    | Last match     |
| `$&`    | Entire match   |

Some regex implementations use \ instead of $.

## Assertions

| Symbol       | Description             |
|--------------|-------------------------|
| `?=`         | Lookahead               |
| `?!`         | Negative lookahead      |
| `?<=`        | Lookbehind              |
| `?!=` `?<!`  | Negative lookbehind     |
| `?>`         | Once-only subexpression |
| `?(...)`     | If condition            |
| `?(...) \| ` | If-else condition       |