regex - How to find word in string using regular expression

Question

How to find word in string using regular expression regardless of case sensitivity ?

Exmaple:

1. A1234_front123 in this need to find _front word
2. a1235Front1234yy in this I need to find front

I need to design generic regular expression which can find any kind of words in given string

Answer 1

If front could be another word, this should try with such combination:

(?<=[0-9])[A-Za-z_]+(?=[0-9_])

DEMO

it will work without case insensitive mode i