Quantifiers

Quantifiers control how many times a pattern can match:

• ? makes a pattern optional (i.e. it matches 0 or 1 times)
• + lets a pattern repeat (i.e. it matches at least once)
• * lets a pattern be optional or repeat (i.e. it matches any number of times, including 0).

# ab? matches an "a", optionally followed by a "b".
str_view(c("a", "ab", "abb"), "ab?")

## [1] │ <a>
## [2] │ <ab>
## [3] │ <ab>b

# ab+ matches an "a", followed by at least one "b".
str_view(c("a", "ab", "abb"), "ab+")

## [2] │ <ab>
## [3] │ <abb>

# ab* matches an "a", followed by any number of "b"s.
str_view(c("a", "ab", "abb"), "ab*")

## [1] │ <a>
## [2] │ <ab>
## [3] │ <abb>