Java RegEx Match; underscore before first decimal point

Question

I am trying to find a Java regex that will match an "_" before the instance of the first decimal point "." Below doesn't seem to be working for me:

_(?=[0-9][0-9]\.)

Anyone have an idea on how I can accomplish this? Example would be:

FileName:

Hello_World_5_01.00.0000

I would like to match the "_" between the characters "5_01."....Keep in mind that the above is an example filename and will vary, but the one constant will be the "_" before the instance of the first "." (decimal point) regardless of the filename itself. Any help is appreciated.

Answer 1

You could match until the first occurrence of an underscore and capture that in a group.

Then match the following 1+ digits, a dot and if there has to be a digit following you can match that as well.

^.*?(_)\d+\.\d

Regex demo

 const regex = /^.*?(_)\\d+\\.\\d/; const str = `Hello_World_5_01.00.0000`; console.log(str.match(regex)[1]);