How to use VIM replacement to use the hit part in the pattern string

Question

The description of the problem is rather obscure, so I will give an example directly
There is a file like this

A1
A2
A3

hopes to be replaced with

F1B1
F2B2
F3B3

How should

be written?

Answer 1

vim’s regular expressions are quite special, see http://vimregex.com/, but it supports back references, but you need to use escaped brackets ( 和 )，然后在替换部分依序引用（如， 1).

:%s:A\(\d\+\):FB:g

Answer 2

:%s/A(d+)/F1B/g
You can use regular expressions after escaping