Looks like it tries wl-copy, then tries xclip and then tries xsel. I have no idea what those are but google says it's for Wayland, so, I think it's a linux function trying to copy to clipboard? I think their problem is with the use of '.then(...=>...)' since there doesn't seem to be a way to tell each function that the nested ones actually finished.
wl-copy is a program to put text into the system clipboard if you're on a wayland-based system (so you can ctrl-v paste it somewhere else). Imagine like, cat ~/.ssh/whatever | wl-copy and then pasting into github or something.
