Regex that won't allow for matches with 2 or more dots?

Question

Right now I have a list of strings, and some of these strings have consecutive dots in them. I want to match everything except those strings with consecutive dots. For example:

fo.o.ba.r = legal --> fo..obar != legal

This is the regex I've tried using, but it doesn't seem to work how I thought it would.

(?!\.{2,})

Can anyone here put me on the right path? Thank you!

Answer 1

From the start of the string to the end of the string, repeat any character inside a group while using negative lookahead for two dots:

^(?:(?!\.{2}).)+$

https://regex101.com/r/M5nhk7/1

Answer 2

You could use a negative lookahead to assert from the start of the string that what is on the right does not contain 2 dots:

^(?!.*\.{2}).+$

Regex demo

That will match:

• ^ Assert the start of the string
• (?! Negative lookahead
  • .* Match any character 0+ times
  • \.{2} Match 2 times a dot
• ) Close negative lookahead
• .+ Match any character 1+ times
• $ Assert the end of the string