Minecraft – How to copy and paste in Minecraft on Linux/Ubuntu 12.04

This actually depends on what version you're using. Since there's no right-click function in the command block menu, you have to use keyboard shortcuts; however, different versions use different shortcuts. Minecraft 1.7.10 and earlier were all made using the shortcuts for Windows and other systems, so if you're using one of those older versions you have to use Ctrl+V to paste. This gets confusing, because other applications still use ⌘ on Mac. However, if you're using any version of 1.8 or later, you can use ⌘ + V, like the other applications on Mac do.

TL;DR ⌘ + V if you're using 1.8 or higher, Ctrl+V if you're on 1.7.10 or lower

The @s selector refers to the entity which is executing that command. Since the command is being executed by a command block, @s is referring to the command block and that's why it's not working.

There is a much easier way of doing this which doesn't require you to test for anything.

To add someone within range to a team: /team join someTeam @a[distance=..5]

And to remove players from the team if they are out of range: /team leave @a[team=someTeam,distance=5..]