Question

I want a regular expression to test that a string meets the following rules:

1. It must not begin with ..
2. It must not end with ..
3. It must not include special characters like !@#$%^&*, but can include ..
4. It must not include two dots . side by side.

Sample valid input:

• na.me (single dot in middle)

Sample invalid input:

• .name (begins with dot)
• name. (ends with dot)
• na..me (includes two dots side-by-side)
• $name (special character not allowed in any position)
• name# (likewise)
• na#me (likewise)

Answer 1

I believe this should work:

^(\w+\.?)*\w+$  

If not in ECMAScript, then replace the \w‘s with [a-zA-Z_0-9].

The approach here is that instead of citing what’s NOT acceptable, it’s easier to cite what’s acceptable.
Translation of the expression is:

• Start with one or many letters, followed by zero or one period (.)
  • All of which can occur zero or many times
• End with at least one letter