正则语法

下面整理出正则表达式的语法规则：

此处以Python为例，参考：Python Regular Expression's Cheat Sheet，正则表达式的基本语法如下：

正则表达式语法

文字版：

• Special Characters
  • \ escape special characters
    • common char need escaple:
      • \
      • [
      • ]
      • (
      • )
      • {
      • }
      • .
      • *
      • +
      • ?
      • ^
      • $
      • |
  • . matches any character
  • ^ matches beginning of string
  • $ matches end of string
  • [5b-d] matches any chars '5', 'b', 'c' or 'd'
  • [^a-c6] matches any char except 'a', 'b', 'c' or '6'
  • R|S matches either regex R or regex S
  • () creates a capture group and indicates precedence
• Quantifiers
  • * 0 or more (append ? for non-greedy)
  • + 1 or more (append ? for non-greedy)
  • ? 0 or 1 (append ? for non-greedy)
  • {m} exactly mm occurrences
  • {m, n} from m to n. m defaults to 0, n to infinity
  • {m, n}? from m to n, as few as possible
• Special sequences
  • \A start of string
  • \b matches empty string at word boundary (between \w and \W)
  • \B matches empty string not at word boundary
  • \d digit
  • \D non-digit
  • \s whitespace: [ \t\n\r\f\v]
  • \S non-whitespace
  • \w alphanumeric: [0-9a-zA-Z_]
  • \W non-alphanumeric
  • \Z end of string
  • \g<id> matches a previously defined group
• Extensions
  • (?iLmsux) Matches empty string, sets re.X flags
  • (?:...) Non-capturing version of regular parentheses
  • (?P<name>...) Creates a named capturing group
  • (?P=name) Matches whatever matched previously named group
  • (?#...) A comment; ignored.
  • (?=...) Lookahead assertion: Matches without consuming
  • (?!...) Negative lookahead assertion
  • (?<=...) Lookbehind assertion: Matches if preceded
  • (?<!...) Negative lookbehind assertion
  • (?(id)yes|no) Match 'yes' if group 'id' matched, else 'no'