Equivalent to substring as regular expression

Question

Ok, I need a general regex that will give me x characters from a string starting at y, as a function of a string substring:

input_str.Substring (y, x)

But like a C # regex.

Example: 1234567890 Substring (5.3) 678

I know what you think, why not just use the substring function? The short answer is that it is like data for an existing function, and in this context it would be impractical to create a whole separate mechanism for parsing the data. We would like this to work without changing the code.

I feel this is really obvious, but I'm pretty inexperienced with regular expressions. Thanks in advance for any help.

Answer 1

.{y}(.{x}).* should do this, I think, then just pull out the capture group.