创建一个正则表达式，以查找用逗号分隔的字符串，而无需重复中间部分

Question

I'm looking for a regex that matches ALL OF and ONLY the following strings boo , foo , tar , boo,foo , boo,tar , foo,tar , foo,boo , tar,boo , tar,foo , boo,foo,tar , boo,tar,foo , tar,boo,foo , tar,foo,boo , foo,boo,tar and foo,tar,boo .

(Strings that repeat themselves such as boo,boo or boo,boo,tar are NOT GOOD)

Plus: I need the Regular Expression itself to contain the strings boo , foo and tar only once each.

So, to recap: I want no repetition both in the matched strings and the regEx itself.

Any way to achieve this result?

this is what I have so far (boo|foo|tar)((,)(boo|foo|tar))*

Answer 1

Try this regex:

^(boo|foo|tar)(?!.*\1)(?:,(boo|foo|tar)(?!.*\2))*$

Click for Demo

Explanation:

• ^ - asserts the start of the string
• (boo|foo|tar) - matches either boo or foo or tar and capture it as group 1
• (?!.*\\1) - Negative lookahead to make sure that whatever is stored in group 1 does not come anywhere else later in the string
• (?:,(boo|foo|tar)(?!.*\\2))*
  • ,(boo|foo|tar) - matches a , followed by either boo or foo or tar and store it as group 2
  • (?!.*\\2) - Negative lookahead to make sure that whatever is stored in group 2 does not come anywhere else later in the string
  • * - matches the above subsequences 0+ times
• $ - asserts the end of the string

Alternative Regex:

^(?:,?(boo|foo|tar)(?!.*\\1))*$