REX Expression Repetition Operators

  • A regular expression may be followed by a repetition operator in order to indicate the number of times it may be repeated.

    Note: Under Windows the operation "{X,Y}" has the syntax "{X-Y}" because Windows will not accept the comma on a command line. Also, N occurrences of an expression implies infinite repetitions but in this program N represents the quantity 32768 which should be a more than adequate substitute in real world text.

  • An expression followed by the operator "{X,Y}" indicates that from X to Y occurrences of the expression are to be located. This notation may take on several forms: "{X}" means X occurrences of the expression, "{X,}" means from X to N occurrences of the expression, and "{,Y}" means from 0 (no occurrences) to Y occurrences of the expression.

  • The "?" operator is a synonym for the operation "{0,1}". Read as: "Zero or one occurrence."

  • The "*" operator is a synonym for the operation "{0,}". Read as: "Zero or more occurrences."

  • The "+" operator is a synonym for the operation "{1,}". Read as: "One or more occurrences."

  • The "=" operator is a synonym for the operation "{1}". Read as: "One occurrence."

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