B.2 Quantifiers

A quantifier is a metacharacter that tells "how many." You put a quantifier after an item to indicate you want to match that item a certain number of times. Quantifiers are listed in Table B-1.

Table B-1. Quantifiers

Quantifier	How many times
*	Zero or more
+	One or more
?	Optional (zero or one)
{x}	Exactly x
{x,}	At least x
{x,y}	At least x, but no more than y

To use a quantifier, put it immediately after the item you want to quantify. Table B-2 shows some regular expressions with quantifiers.

Table B-2. Quantifier examples

Regular expression	Meaning	Matches	Doesn't match
ba+	b, then at least one a	ba, baa, baaa, rhumba, babar	b, abs, taaa-daaa, celeste
ba+na*s	b, at least one a, n, zero or more a, s	turbans, baanas, rhumbanas!	banana, bananas
ba(na){2}	ba, then na twice	banana, bananas, semi-banana, bananarama	cabana, banarama
ba{2,}ba{3,}	b, then at least two a, then b, then at least three a	baabaaa, baaaaabaaaaa, rhumbaabaaas	baabaa, babaaar, banana
(baa-){2,4}baa	baa- at least two, but not more than four times, then baa	baa-baa-baa, baa-baa-baa-baa-baa, oomp-pa-pa-baa-baa-baa-oomp-pa-pa	baa-baa, baa-baad-news
dogs? and cats?( and chickens?)?	dog, then an optional s, then and cat, then an optional s, then an optional and chicken or and chickens	dog and cat and chicken, dog and cat and chickens, hotdogs and cats, dogs and cat and chickens, dog and cats and chicken, dog and cat and chickensoup	doggies and cats, dogs and cats or chickens, dogss and catss, dog and cat and chickenlegs

Use the ? quantifier to indicate that something is optional, like in the U.S. ZIP Code pattern at the start of this appendix. A syntactically valid ZIP Code can be five digits, or five digits, a hyphen, and four more digits. The hyphen and last four digits are optional. Just like any other quantifier, to make ? apply to the entire optional section, the characters that match the hyphen and digits have to be grouped with parentheses.