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!

@WiktorStribiżew Your regex seems to be working with all the strings I have. I will accept your answer if you post the regex in the answer section. Thank you! — Pulkit Mittal
– Pulkit Mittal, Commented Nov 13, 2017 at 8:54
anubhava's regex is almost the same, a tiny bit optimized. Just .+? matches 1 or more chars , and I used .*?, 0 or more chars at the start. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Nov 13, 2017 at 8:56

anubhava · Accepted Answer · 2017-11-13 08:47:05Z

2

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.

answered Nov 13, 2017 at 8:47

anubhava

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2 Comments

Pulkit Mittal Over a year ago

This works! But Wiktor's regex also works, and since he answered first, I would accept his answer. Unless you find an issue with it? Thank you for your answer as well!

anubhava Over a year ago

I just checked Wiktor's regex. No I don't find any issue with that as both regex are almost similar.

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