How does this regex work and how do i make it repeat only 5 times?

Question

What does this regex do? i know it replaces the filename (but not extension)

    Regex r = new Regex("(?<!\\.[0-9a-z]*)[0-9]");
    return r.Replace(sz, "#");

How do i make it only repeat 5 times? to make it convert "1111111111.000" to "11111#####.000" ?

Answer 1

Try changing the asterisk after the closing bracket to "{5}" (no quotes). This depends a bit on your regex environment's feature set, but that is a common syntax.

Answer 2

The regex matches a character (0 to 9) that is not preceded by a dot then any number of 0 to 9 or a to z's.

The replace line is responsible for the multi replacements. So you want to use the Replace method the has an extra parameter count.

so the code would look like:

 Regex r = new Regex("(?<!\\.[0-9a-z]*)[0-9]");
 return r.Replace(sz, "#", 5);

Answer 3

I havent' tried this but Have tried it, works: how about changing the general pattern to use a positive lookahead instead? That way, it should work:

[0-9a-z](?=[0-9a-z]{0,4}\.)

Basically, this finds any (alphanumeric) character followed by up to four other alphanumeric characters and a period. This might just work to match the last five characters in front of the period consecutively. It's hellishly inefficient though, and it only works with engines that allow variable-width lookahead patterns.