Regex CheatSheet

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基础

  • dot . matches anything except for a newline

  • \d matches any digit [0-9]

  • \D matches any character that is not a digit.

  • \s matches any whitespace character [ \r\n\t\f ].

  • \S matches any non-whitespace character

  • \w matches any word character, Word characters include alphanumeric characters (a-z, A-Z and 0-9) and underscores (_).

  • \W matches any non-word character

  • ^ matches the position at the start of a string

  • $ matches the position at the end of a string

重复

  • * matches zero or more repetitions of character/character class/group

  • + matches one or more repetitions of character/character class/group

  • ? 匹配 0 或者 1 个某字符。例如 a? 表示 zero or one of a

  • {x} will match exactly x repetitions of character/character class/groups

  • {x,y} will match between x and y (both inclusive) repetitions of character/character class/groups。当省略 y 时表示重复 >= x 次。

Character Class

  • [] matches only one out of several characters placed inside the square brackets.

  • [^] matches any character that is not in the square brackets.

字符范围，常用的有 [a-z]，[A-Z]，[0-9]

Grouping and Capturing

  • \b assert position at a word boundary.

Three different positions qualify for word boundaries : ► Before the first character in the string, if the first character is a word character. ► Between two characters in the string, where one is a word character and the other is not a word character. ► After the last character in the string, if the last character is a word character.

  • () around a regular expression can group that part of regex together.

  • (?: ) can be used to create a non-capturing group. It is useful if we do not need the group to capture its match.

  • | 表示或者，match a single item out of several possible items separated by the vertical bar. When used inside a character class, it will match characters; when used inside a group, it will match entire expressions (i.e., everything to the left or everything to the right of the vertical bar). 也就是说 | 可以用在 [] 或者 () 中。

Backreferences

  • \group_number：This tool (\1 references the first capturing group) matches the same text as previously matched by the capturing group. 比如，(\d)\1: It can match 00, 11, 22, 33, 44, 55, 66, 77, 88 or 99.

Assertions

  • Positive lookahead：regex_1(?=regex_2) asserts regex_1 to be immediately followed by regex_2. The lookahead is excluded from the match. It does not return matches of regex_2. The lookahead only asserts whether a match is possible or not.
  • Negative lookahead: regex_1(?!regex_2) asserts regex_1 not to be immediately followed by regex_2. Lookahead is excluded from the match (do not consume matches of regex_2), but only assert whether a match is possible or not.
  • Positive lookbehind: (?<=regex_2)regex_1 asserts regex_1 to be immediately preceded by regex_2. Lookbehind is excluded from the match (do not consume matches of regex_2), but only assert whether a match is possible or not.
  • Negative lookbehind: (?<!regex_2)regex_1 asserts regex_1 not to be immediately preceded by regex_2. Lookbehind is excluded from the match (do not consume matches of regex_2), but only assert whether a match is possible or not.

补充

  • *? 表示非贪婪匹配，即“尽可能少的匹配”。如 r\w*? 对于 r, re, regex 都只会匹配到 r，而 r\w* 则会匹配到整个单词。

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