Rename multiple files at once

[Pieter Verberne]

Hi there,

How do I rename multiple files at once? I want to rename a list of
files like:

file.jpg
file1.jpg
file_2.jpg

to:

file_thumb.jpg
file1_thumb.jpg
file_2_thumb.jpg

man mv(1) says nothing about REGEX. (although I don't know REGEX
(yet))

Kind regard,
Pieter Verberne