Lessons · Regex · + * ? quantifiers

How many times

A quantifier says how many of the thing before it: ? is 0 or 1, * is 0 or more, + is 1 or more, {n} exactly n, {n,m} between.

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What it is for

Almost nothing in real text is a fixed length. Postcodes, prices, names, ids: quantifiers are what let one pattern cover them all.

How to think about it

Which character, and how many of it? Describe one character first (a digit, a letter, a class), then attach the count. Ask whether zero is allowed; that is the difference between * and +.

Worked example

pattern: colou?r

u is optional: 0 or 1 of it.

text: color and colour

Both spellings match.

pattern: ^\d{2,3}$

Two or three digits, whole string.

text: 42

Match. 4 alone would not; 4242 would not.

Your turn

One or more letters.

[a-z]

The trap

* matches nothing at all, so a* matches the empty string in any text. When you mean 'some', use +.

Practise + * ? quantifiers on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.