set nu

syntax on
set tags=tags;
set autochdir

"How can I open a NERDTree automatically when vim starts up if no files were specified?
autocmd StdinReadPre * let s:std_in=1
autocmd VimEnter * if argc() == 0 && !exists("s:std_in") | NERDTree | endif

"How can I close vim if the only window left open is a NERDTree?
autocmd bufenter * if (winnr("$") == 1 && exists("b:NERDTreeType") && b:NERDTreeType == "primary") | q | endif

nmap be :BufExplorer<CR>
nmap nt :NERDTree<CR>
nmap tl :Tlist<CR>