Self-tutoring about Notepad++: the tutor mentions using regular expressions.
Regular expressions can be used in Notepad++ Search and Replace. For instance, suppose you want to change the variable names test2 test39 test991 to test_2 test_39 test_991 . In Notepad++, such change would be possible using Search with a regular expression
Replace (test)([0-9]+) with \1_\2
Source:Oracle Tutoring by Jack and Diane, Campbell River, BC.