识别罗马数字后跟“.”、空格和大写字母。 （正则表达式）

Question

Can someone please help me with this?

I'm trying to match roman numerals with a "." at the end and then a space and a capital letter after the point. For example:

I. And here is a line.

II. And here is another line.

X. Here is again another line.

So, the regex should match the "I. A" , "II. A" and "X. H" .

I did this "^(XC|XL|L?X{0,3})(IX|IV|V?I{0,3}){1,4}\.\s[AZ]" But the problem is that this RegEx is also matching with ". A" and i don't want it.

In resume it should have at least one roman numeral, followed by a "." and then a space and a capital letter.

Answer 1

You need a (?=[LXVI]) lookahead at the start that would require at least one Roman number letter at the start of the string:

^(?=[LXVI])(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})\.\s[A-Z]
# ^^^^^^^^^

See the regex demo . Not sure why you used {1,4} , I suggest removing it.

Another workaround here would be to use a word boundary right after ^ :

^\b(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})\.\s[A-Z]
#^^

This would disallow a match where . appears at the start since \b , required at the same position as the start of string, requires that the next char must be a word char (and here, it must be a Roman number).

Regarding \.\s[AZ] , you may enhance it you add + or * after \s , and if you ever need to match it and exclude from a match, turn it into a positive lookahead, (?=\.\s+[AZ]) or (?=\.\s*[AZ]) .