Unexpected match of regex

Question

I expect the regex pattern ab{,2}c to match only with a followed by 0, 1 or 2 bs, followed by c.

It works that wa

Answer 1

I am writing this as an answer, because unfortunately I cant add a comment.

Update: Following the answer by Wiktor Stribiżew and feedback, seems the behavior is categories as a bug.

Original: The syntax you are using is just not supported in R (assuming the default engine). This is why you are getting unexpected results.

• The supported syntax is {n,m} as the documentation states. Thus, you need to specify both boundaries, e.g. {0,2}, which will return the correct result.
• The syntax {,m}, on the other hand, is missing from the documentation to regex, which silently indicates that it is not supported.

In case you would like to explore differences in syntax, I would recommend taking a look at the regular-expressions.info comparison page. (You need to compare Python and R in terms of Quantifiers in this case.)