when Ruby file run with Ruby, when Gemfile run bundle

ruby.vim

set shiftwidth=2
set softtabstop=2

function Rb_or_gemfile()
  if bufname('%') == 'Gemfile'
    execute '!bundle'
  else
    execute '!ruby %'
  endif
endfunction

map <C-j> :w <CR>:call Rb_or_gemfile()<CR>