根据nerdtree安装说明，我需要安装pathogen.vim来安装nerdtree。要安装pathogen.vim，我按照病原体安装说明操作，我这样做了：
~$ mkdir -p ~/.vim/autoload ~/.vim/bundle; \
> curl -so ~/.vim/autoload/pathogen.vim \
> <link to github>
这创造了pathogen.vim：
~/.vim/autoload$ ls
pathogen.vim … … …
然后我按照病原体安装说明进行操作：
Add this to your vimrc:
call pathogen#infect()
==
~$ cat .vimrc
…
…
"For pathogen(a vim installer):
call pathogen#infect()
然后按照nerdtree安装说明进行操作：
pathogen.vim is the recommended way to install nerdtree.
cd ~/.vim/bundle
git clone <link to github>
Then reload vim, run :helptags, and check out :help NERD_tree.txt.
我试着像这样安装nerdtree：
~/.vim/bundle$ git clone <link to github>
Cloning into 'nerdtree'...
remote: Counting objects: 2426, done.
remote: Compressing objects: 100% (801/801), done.
remote: Total 2426 (delta 1091), reused 2354 (delta 1025)
Receiving objects: 100% (2426/2426), 912.52 KiB | 573 KiB/s, done.
Resolving deltas: 100% (1091/1091), done.
$
哪个产生了：
~/.vim$ cd bundle
~/.vim/bundle$ ls
nerdtree
但我无法让nerdtree工作。当我尝试这个时：
~$ cd rails_projects/demo_app22/
~/rails_projects/demo_app22$ mvim .
~/rails_projects/demo_app22$
...然后这个：
:NERDtree
我收到错误：
E492: Not an editor command: NERDtree
当我尝试：helptags时，我收到错误：
E472: Argument required