![无法为 [FishShell] 创建配置目录 请设置 $XDG_CONFIG_HOME 变量](https://linux22.com/image/35685/%E6%97%A0%E6%B3%95%E4%B8%BA%20%5BFishShell%5D%20%E5%88%9B%E5%BB%BA%E9%85%8D%E7%BD%AE%E7%9B%AE%E5%BD%95%20%E8%AF%B7%E8%AE%BE%E7%BD%AE%20%24XDG_CONFIG_HOME%20%E5%8F%98%E9%87%8F.png)
启动fishshell时出现此错误：
melanie:~ melanie$ fish
fish: Unable to create a configuration directory for fish. Your personal
settings will not be saved. Please set the $XDG_CONFIG_HOME variable to
a directory where the current user has write access.
我如何设置该变量？