Bash version 4 introduced a new option called globstar. When the option is set, recursive globbing with ** is enabled.

Lets say you want to move all files from a directory and its subdirectories. Most common method would be to use the find command.

For example, find and move all .mp3 files from the current and all subdirectories to a directory named music.

$ sudo find . -type f -exec mv *.mp3 /music {} \;

The can be simplified by enabling the Bash option globstar.

$ shopt -s globstar

$ shopt |grep globstar
globstar        on

With the BASH globstar setting enabled the command is as simple as:

$ mv **/*.mp3 /music