Insert a string before a matching string or at the end using regex

Question

I have a requirement where the string has to contain _exact. I am using Java.

• If the string has a locale (_en or _ja) at the end, add _exact before the locale.
• If _exact is already present, don't add it again.
• If no locale at the end, and no exact, add _exact at the end of the string.

E.g.:

• something -> something_exact
• something_en -> something_exact_en
• something_ja -> something_exact_ja
• something_exact_en -> something_exact_en
• something_exact -> something_exact

I spent some time and came up with 2 regex that, if ran in succession on the same string, make it possible. I am not sure if they cover all the possible cases though.

^(.*)(?<!_exact)(_(?:en|ja))$

^(.*)(?<!_exact)(?<!_(?:en|ja))$

If anybody could help me come up with just 1 regex that does the job, it would be great! Thank you!

Answer 1

You can use this regex:

str = str.replaceAll("^(?!.*_exact(?:_en|_ja)?$)(.+?)(_en|_ja)?$", "$1_exact$2");

RegEx Demo

• (?!.*_exact(?:_en|_ja)?$) is a negative lookahead that skips inputs that ends with _exact or _exact_en or _exact_ja.