Zsh – Make Completion Show First Guess on Same Line Like Fish

To request that a command be completed like another command that is already known to the completion system, you can use the compdef my_command=known_command form of compdef.

compdef s=ssh
compdef {cxterm,uxterm,xterm-color}=xterm

Under the hood, this is basically equivalent to _comps[s]=$_comps[ssh].

Some completion commands apply to a family of functions and read the first word of the command line to determine which particular command to complete. For example, the commands ssh, scp, sftp and a few more are all completed by the function _ssh. In that case, you need to tell the completion function which “service” your function is like (by default, the service is the executable name, here your function's name).

_s () {
  local service=ssh
  _ssh "$@"
}
compdef _s s

Add this line to your ~/.zshrc:

setopt menu_complete

See man zshoptions for details.