Regular Expression to Match Number of Lines and Characters per Line

Question

I'm trying to make sure that a string contains between 0 and 3 lines, and that for a given line that is present that it contains 0 to 100 characters. It would need to be a valid expression for JavaScript and Java. Like many people doing RegEx I'm copying from various spots on the Internet. Working backwards I think `^.{0,100}$` gets me the "line contains 0 to 100 characters", but trying to group that as `(^.{0,100}$){0,3}` doesn't work. The new line character is probably part of my problem, so I ended up with something like `.{0,100}(?:
.{0,100}){0,2}` trying to say "a line of 0 to 100 characters optionally followed by 0 to 2 instances of a new line and 0 to 100 more characters", but that also failed. Up until now I got those expressions from other people. Using an online test tool I finally monkeyed this together: `^.{0,100}(?:(?:
|[
]).{0,100}){0,2}$` which appears to work. So, my question is, am I missing any pitfalls in `^.{0,100}(?:(?:
|[
]).{0,100}){0,2}$` given wha…

Accepted Answer

I think what you have will work fine. You can make the line break part a little more compact if you want, and you don't need `^` and `$` if you are using `matches()`:

```
String regex = ".{0,100}(?:[
]+.{0,100}){0,2}";
```

EDIT

After some more thoughts I realized the newline suggestion above will match 4 (or more) lines as long as a couple of them are empty. So, we are back to your suggested example. Oh well, at least the start and end characters can be omitted.

```
String regex = ".{0,100}(?:(?:
|[
]).{0,100}){0,2}";
```

Regular Expression to Match Number of Lines and Characters per Line

Solution

Problem