Regular Expressions

• A regular expression (RE) is:

  • A single character
  • The empty string, _
  • The concatenation of two regular expressions

    • Notation: RE1 RE2 (i.e. RE1 followed by RE2)
  • The union of two regular expressions

    • Notation: RE1 | RE2
  • The closure of a regular expression

    • Notation: RE*
    • * is known as the Kleene star
    • * represents the concatenation of 0 or more strings

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