Regex replace any number of matches at the start of the line

Question

I have text with this structure:

1.  Text1
2.  Text 2. It has a number with a dot.
3.  1.   Text31

I want to get this text:

# Text1
# Text 2. It has a number with a dot. (notice that this number did not get replaced)
## Text31

I tried doing the following but it does not work

var pattern = @"^(\s*\d+\.\s*)+";
var replaced = Regex.Replace(str, pattern, "#", RegexOptions.Multiline);

Basically, it should start matching at the start of every line and replace every matched group with # symbol. Currently, if more than one group is matched, everything is replaced by a single # symbol. Pattern I am using is probably incorrect, can anyone come up with a solution?

Answer 1

You may use

(?:\G|^)\s*\d+\.

It matches the start of string or the end of the previous successful match or start of a line, and then zero or more whitespaces, one or more digits and a dot.

Details

• (?:\G|^) - start of string or end of the previous match (\G) or the start of a line (^)
• \s* - zero or more whitespaces if you want to only match horizontal whitespaces to avoid overflowing to the next lie(s) replace with [\s-[\r\n]]* or [\p{Zs}\t]*)
• \d+ - one or more digits (to match only ASCII digits, replace with [0-9]+ or pass the RegexOptions.ECMAScript option to the Regex constructor)
• \. - a dot.

The RegexOptions.Multiline option must be passed to the Regex constructor to make ^ match the start of a line. Or add an inline version of the anchor, (?m), at the start of the pattern.

For more details about \G anchor, see Continuing at The End of The Previous Match.

See the RegexStorm demo.