Why can’t I make a group repeat in regex Java?

I have a regex I want to construct for validating the UNC syntax, which is:

\serversharedfolderpath

I don’t care about the server or folder characters, I exclusively want to validate the thing1thing2maybe3 syntax, the server and folder names will be validated separately.

This is what I have so far:

(^\\w+)(\{1}w+)+(.+(?<!\)$)

These are my tests:

1. MATCH – \servermultiplefoldersexamplepath
2. FAIL – \server\multiplefoldersexamplepath
3. SHOULD FAIL – \servermultiple\foldersexamplepath
4. FAIL – \servermultiplefoldersexamplepath
5. FAIL – \server
6. FAIL – \servermultiple
7. SHOULD MATCH – \serverm
8. MATCH – \servermwz

I’m testing here: https://regex101.com/r/WqF7h7/1

Can anyone help making #3 and #7 fail and match respectively?

#3 has a second double slash after “multiple”, this shouldn’t be permitted, only at the beginning should there be double slashes. This should fail like #2

#7 has the correct syntax and should be matching like #8

Thanks.

Answer

You can use

^\{1,2}w+(?:\w+)+$

In Java with the doubled backslashes:

String regex = "^\\{1,2}\w+(?:\\\w+)+$";

The pattern matches:

• ^ Start of string
• \{1,2} Match 1 or 2 backslashes
• w+ Match 1+ word characters
• (?:\w+)+ Repeat 1+ times 1 or more word characters
• $ End of string

Regex demo

Or a bit less strict version matching any char except instead of only word characters:

^\{1,2}[^\]+(?:\[^\]+)+$