检查单词前后的字符

Question

I need to have a one positive regex which combines all 3 of the following:

-- ^(.*)\.abc\.(.*)$
-- ^(.*)\.abc$
-- ^abc\.(.*)$

such that the below cases do not apply to the regex:

-- 123abc
-- .abc123
-- 123abc.

and the following fgive the positive result:

--.abc
--.abc.
--abc.

I know that the 3 conditions can be in ORed in a group. I am looking fr a better solutoin, probably using lookaheads.

I tried using backreferencing : /^.*([\\.]*)abc\\1.*$/ but then this is positive for negative cases as well.

Answer 1

You can use this regex:

^(.*([.;]))?abc((?=[.;])\2.*)?$

RegEx Demo

RegEx Breakup:

• ^ : Start
• (.*([.;]))? : start with anything followed by dot or semicolon (optional match). Note that we capture before abc in capture group #2
• abc : match abc
• ((?=[.;])\\2.*)? : End with same character we captured before abc and anything following (optional match). Lookahead assertion is used to make sure we don't match empty back-reference \\2
• $ : End