Repeated occurrences

So far, we saw how we can match fixed characters or numeric patterns. Most often, you want to handle certain repetitive natures of patterns also. For example, if I want to match 4 as, I can write /aaaa/, but what if I want to specify a pattern that can match any number of as?

Regular expressions provide you with a wide variety of repetition quantifiers. Repetition quantifiers let us specify how many times a particular pattern can occur. We can specify fixed values (characters should appear n times) and variable values (characters can appear at least n times till they appear m times). The following table lists the various repetition quantifiers:

• ?: Either 0 or 1 occurrence (marks the occurrence as optional)

• *: 0 or more occurrences

• +: 1 or more occurrences

• {n}: Exactly n occurrences

• {n,m}: Occurrences between n and m

• {n,}: At least an n occurrence

• {,n}: 0 to n occurrences

In the following example, we create a pattern where the character u is optional (has 0 or 1 occurrence...