Rename multiple files, but only rename part of the filename in Bash

If you have all of these files in one folder and you’re on Linux you can use:

rename 's/test-this/REPLACESTRING/g' *

The result will be:

REPLACESTRING.ext
REPLACESTRING.volume001+02.ext
REPLACESTRING.volume002+04.ext
...

rename can take a command as the first argument. The command here consists of four parts:

1. s: flag to substitute a string with another string,
2. test-this: the string you want to replace,
3. REPLACESTRING: the string you want to replace the search string with, and
4. g: a flag indicating that all matches of the search string shall be replaced, i.e. if the filename is test-this-abc-test-this.ext the result will be REPLACESTRING-abc-REPLACESTRING.ext.

Refer to man sed for a detailed description of the flags.