If you are using vim in MAC OSX, unfortunately it comes with older verion, and not complied with clipboard options. Luckily, homebrew can easily solve this problem.
install vim:
brew install vim --with-lua --with-override-system-vim
install gui verion of vim:
brew install macvim --with-lua --with-override-system-vim
restart the terminal to take effect.
append the following line to ~/.vimrc
set clipboard=unnamed
now you can copy the line in vim with yy
and paste it system-wide.