Vim script check running platform

i manage to answer my own question, for comparing string in vimscript we should use =~ instead of == . The reverse one is !~

So edit this line if s:uname == "Darwin" to if s:uname =~ "Darwin" to make this little script work.

I rewrite this as function:

function! GetRunningOS()
  if has("win32")
    return "win"
  endif
  if has("unix")
    if system('uname')=~'Darwin'
      return "mac"
    else
      return "linux"
    endif
  endif
endfunction
let os=GetRunningOS()

In case, someone interest in my .vimrc, check my dotFiles