# Regular Expressions Cheat Sheet

A regular expression specifies a set of strings that matches it. This cheat sheet is based off Python 3's Regular Expressions (http://docs.python.org/3/library/re.html) but is designed for searches within Sublime Text.

## Special Characters

|     |                                                             |
| --- | ----------------------------------------------------------- |
| `\` | Escapes special characters or signals a special sequence.   |
| `.` | Matches any single character except a newline.              |
| `^` | Matches the start of the string.                            |
| `$` | Matches the end of the string​                              |
| `*` | Greedily matches 0 or more repetitions of the preceding RE. |
|     |                                                             |
|     |                                                             |
|     |                                                             |
|     |                                                             |

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`*?`              Matches 0 or more repetitions of the preceding RE.

+     Greedily matches 1 or more repetitions of the preceding RE.
  
  +?                Matches 1 or more repetitions of the preceding RE.
  ?                Greedily matches 0 or 1 repetitions of the preceding RE.
  ??                Matches 0 or 1 repetitions of the preceding RE.
  A|B                Matches A, if A is unmatched then matches B, where A and B are arbitrary REs.
  {m}                Matches exactly m many repetitions of the previous RE.
  {m,n}            Greedily matches from m many to n many repetitions of the previous RE.
  {m,n}?            Matches m many to n many repetitions of the previous RE.

[...]            Indicates a set of characters to match.
    [amk]                Matches 'a', 'm', or 'k'.
    [a-z]                Matches 'a' through 'z'.
    [a-f0-7]            Matches 'a' through 'f' or '0' through '7'.
    [a\-z]                Matches 'a', '-', or 'z'.
    [a-]                Matches 'a' or '-'.
    [-a]                Matches 'a' or '-'.
    [(+*)]                Matches '(', '+', '*', or ')'. [] matches special characters literally.
    [\w]                Matches the character class for '\w'. See character classes.
    [^5]                Matches anything other than '5'. '^' forms the complementary set only as the first character in a set.
    []()]                Matches ']', '(', and ')'. ']' is taken literally only as the first character in a set.
    [()\]]                Matches ']', '(', and ')'.

(...)            Matches the RE inside the parenthesis and assigns a new group.
(?P<name>...)    The RE matched is accessible by the group indicated by name.

(?...)            Extension notation which changes a RE's behavior. These do not assign a new group.
    (?aiLmsux)            Sets the corresponding flag to each letter. Does not work within Sublime Text.
    (?:...)                A non-capturing version of parenthesis. The matched substring cannot be retrieved later.
    (?P=name)            Matches the substring matched by the group named name.
    (?#...)                A comment, the contents are ignored.
    (?=...)                Lookahead assertion, the preceding RE only matches if this matches.
    (?!...)                Negative lookahead assestion, the preceding RE only matches if this doesn't match.
    (?<=...)            Positive lookbehind assertion, the following RE will only match if preceeded with this fixed length RE.
    (?<!...)            Negative lookbehind assertion, the following RE will only match if not preceeded with this fixed length RE.
    (?(id)true|false)    If group id exists then uses the true RE, else use the false RE.

>    Character classes
> \1                Matches the contents of the group labelled by the same number. Acceptable numbers are 1-99.
> \A                Matches at the start of the current string.
> \b                Matches the empty string at the beginning or end of a word. \b matches the boundary between \w and \W.
> \B                Matches the empty string not at the beginning or end of a word.
> \d                Matches any Unicode decimal digit, including 0-9.
> \D                Matches any Unicode non-decimal digit.
> \s                Matches any Unicode whitespace character, including ' ', \t, \n, \r, \f and \v.
> \S                Matches any Unicode non-whitespace character.
> \w                Matches any Unicode word character, including a-z, A-Z, and 0-9.
> \W                Matches any Unicode non-word character.
> \Z                Matches at the end of the string.

\a                Matches the ASCII Bell ().
\f                Matches the ASCII Formfeed ().
\n                Matches the ASCII Linefeed.
\r                Matches the ASCII Carriage Return (
).
\t                Matches the ASCII Horizontal Tab.
\v                Matches the ASCII Vertical Tab ().