Regex that does not allow consecutive dots
You can use it like this with additional lookaheads:
^(?!\.)(?!.*\.$)(?!.*?\.\.)[a-zA-Z0-9_.]+$
-
(?!\.)- don't allow.at start -
(?!.*?\.\.)- don't allow 2 consecutive dots -
(?!.*\.$)- don't allow.at end
Re-write the regex as
^[a-zA-Z0-9_]+(?:\.[a-zA-Z0-9_]+)*$
or (in case your regex flavor is ECMAScript compliant where \w = [a-zA-Z0-9_]):
^\w+(?:\.\w+)*$
See the regex demo
Details:
-
^- start of string -
[a-zA-Z0-9_]+- 1 or more word chars -
(?:\.[a-zA-Z0-9_]+)*- zero or more sequences of:-
\.- a dot -
[a-zA-Z0-9_]+- 1 or more word chars
-
-
$- end of string