Regex that does not allow consecutive dots

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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

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