regular expressions: match x times OR y times

Question

Lets say I need to match a pattern if it appears 3 or 6 times in a row. The closest I can get is something like \\d{3,6} but that doesn\'t quite do what I need.

\'12

Answer 1

^(\d{3}|\d{6})$

You have to have some sort of terminator otherwise \d{3} will match 1234. That's why I put ^ and $ above. One alternative is to use lookarounds:

(?

to make sure it's not preceded by or followed by a digit (in this case). More in Lookahead and Lookbehind Zero-Width Assertions.