我怎样才能在正则表达式中限制点一次或可选

Question

A regex is needed which should have only special character dot which should either be optional or occur only once.

pattern = /^([A-Za-z.]+)$/;

Answer 1

Without more information I'd use

/^(?!$)[a-z]*\.?[a-z]*$/i

The negative lookahead prevents empty matches.

See this demo at regex101

Answer 2

Here are some ways to do it:

1. Deal separately where the input has has one dot, with optional letters surrounding it, or no dot (but then having at least one letter):

   /^([az]*\.[az]*|[az]+)$/i

2. Just capture letters and dots like you did, but don't allow the input to have two dots, using a negative look ahead:

   /^(?.(.*\.){2})([az.]+)$/i

3. Capture optional letters then an optional point and then optional letters, but forbid an empty input with a negative look-ahead:

   /^(?.$)([az]*\??[az]*)$/i

Answer 3

If in any case the dot should not be at the start or end and not match an empty string, you can start the match with 1 or more chars az and then optionally match a dot and again 1 or more chars az:

/^[a-z]+(?:\.[a-z]+)?$/i

Regex demo