匹配可能包含1-2位数的单词

Question

I use the following regex for matching words with a length of 4 that has 1 number and 3 capital letters:

\b(?=[A-Z]*\d[A-Z]*\b)[A-Z\d]{4}\b

What I would like to know is how I need to modify the expression to filter out words with a length of 10, that contains 0-2 numbers.

\b(?=[A-Z]*\d[A-Z]*\b)[A-Z\d]{10}\b

This will work for 1 number occurence, but how do i extend it to filter 0 and 2 numbers as well?

Sample: http://regexr.com?32u40

Answer 1

Put the length check into the lookahead:

\b(?=[A-Z\d]{10}\b)(?:[A-Z]*\d){0,2}[A-Z]*\b

Explanation:

\b           # Start at a word boundary
(?=          # Assert that...
 [A-Z\d]{10} # 10 A-Z/digits follow
 \b          # until the next word boundary.
)            # (End of lookahead)
(?:          # Match...
 [A-Z]*      # Any number of ASCII uppercase letters
 \d          # and exactly one digit
){0,2}       # repeat 0, 1 or 2 times.
[A-Z]*       # Match any number of letters
\b           # until the next word boundary.