Regex: How to optionally match something at beginning or end, but not both?

Question

I have situation where in the regular expression is something like this: `^b?A+b?$` So `b` may match at the start of the string 0 or 1 times, and `A` must match one or more times. Again `b` may match at the end of the string 0 or 1 times. Now I want to modify this regular expression in such way that it may match `b` either at the start or at the end of the string, but not both. How do I do this?

Accepted Answer

Theres a nice "or" operator in regexps you can use.

```
^(b?A+|A+b?)$
```

Regex: How to optionally match something at beginning or end, but not both?

Solution

Problem