🔤 Regular Expressions

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Regular Expression Operators

Basic Characters

• Dot (.):
  Matches any single character except for a newline.

• Literal Characters (a, B, 5):
  Any normal character matches itself exactly.

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Quantifiers (How many times)

• Main Quantifiers:
  Specifies how many times the preceding part can repeat.

  • * (Asterisk): Matches zero or more times.
  • + (Plus): Matches one or more times.
  • ? (Question Mark): Matches zero or one time.

• Brace Quantifiers:
  Allows you to specify exact counts.

  • {n}: Matches exactly n times.
  • {n,}: Matches n or more times.
  • {n,m}: Matches between n and m times.

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Character Classes (What kind)

• Brackets ([abc]):
  Matches any single character inside the brackets.

• Negated Brackets ([^abc]):
  Matches any single character not inside the brackets.

• Range ([a-z]):
  Matches any single character in the specified range.

• Shorthand Classes:

  • \d: Matches any digit. (Same as [0-9])
  • \w: Matches any word character. (Same as [a-zA-Z0-9_])
  • \s: Matches any whitespace character.

• Negated Shorthands:

  • \D: Matches any non-digit.
  • \W: Matches any non-word character.
  • \S: Matches any non-whitespace character.

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Anchors (Where)

• Caret (^):
  Matches the start of the string.

• Dollar Sign ($):
  Matches the end of the string.

• Word Boundary (\b):
  Matches the position between a word character and a non-word character.

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Grouping and Alternation

• Parentheses ((...)):
  Groups part of the expression together and captures the match.

• Pipe (|):
  Acts as an OR operator.
  (e.g., cat|dog matches "cat" or "dog")

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Escaping

• Backslash (\):
  Escapes a special character to treat it as a literal.
  (e.g., use \. to match a literal dot)