arhc where does mointed devicec go code example

Example 1: What does @variable stand for in Ruby

@variable - is an "instance" variable. 
It can be accessed with any method inside the class.

Example 2: what does worktree prune do

$ mkdir a
$ cd a
$ git init
$ git commit --allow-empty --allow-empty-message -m ''
$ git worktree add ../b
$ ls .git/worktrees/
b
$ rm -rf ../b
$ git worktree prune
$ ls .git/worktrees/
$