go to previous page   go to home page   go to next page


Language Example Strings Regular Expression
Any number of A's or any number of B's AAA BBBB Ø A*|B*
One or more A's or any single character not an AAAA C x A+|[^A]
An integer or a decimal fraction143 834.91 89.0 [0-9]+|[0-9]+\.[0-9]+


Regular Expression
(Delimit with quotes)
(Delimit with quotes)

Rule 11:  Parentheses

Parentheses are used to group subexpressions. A subexpression inside parentheses must be completely matched. For example, (cat|snake) eyes matches cat eyes or snake eyes.

Parentheses have high precidence, so that what lies between them is a complete subexpression.   (cat|snake) eyes means cat or snake, followed by eyes.

Regular ExpressionMatches Does Not Match
puppy|ies "puppy" or "ies" "puppies"
pupp(y|ies) "puppy" or "puppies" "ies"
puppy* "pupp", "puppy", "puppyy", "puppyyy", . . . "puppypuppy"
(puppy)* Ø, "puppy", "puppypuppy", "puppypuppypuppy", . . . "ppyyyy"
(puppy)+ "puppy", "puppypuppy", "puppypuppypuppy", . . . Ø, "pupp"
(puppy)? Ø, "puppy" "puppypuppy"
(dog |cat |bat )+"dog ", "dog cat dog ", "bat bat bat " "dog", "dogcatbat"

The *, +, and ? quantifiers apply to the single character to their left, or to the parenthetical subexpression to their left.


Write a regular expression to match:

"porkchop", "lambchop", "Porkchop", "Lambchop",
"porkchops", "lambchops", "Porkchops", or "Lambchops".