Setting netrw like NERDTree

Starting with netrw v150, there's :Lexplore, which will toggle a netrw window on the left-hand side.

I just did some improvements on Nick's solution which fixes:

• opens 100% high window (independent from window splits)
• :Lexplore opens it on left side, :Lexplore! on the right
• listing the directory of the current file (even on remote directories)

Put these lines to the end of your .vimrc:

com!  -nargs=* -bar -bang -complete=dir  Lexplore  call netrw#Lexplore(<q-args>, <bang>0)

fun! Lexplore(dir, right)
  if exists("t:netrw_lexbufnr")
  " close down netrw explorer window
  let lexwinnr = bufwinnr(t:netrw_lexbufnr)
  if lexwinnr != -1
    let curwin = winnr()
    exe lexwinnr."wincmd w"
    close
    exe curwin."wincmd w"
  endif
  unlet t:netrw_lexbufnr

  else
    " open netrw explorer window in the dir of current file
    " (even on remote files)
    let path = substitute(exists("b:netrw_curdir")? b:netrw_curdir : expand("%:p"), '^\(.*[/\\]\)[^/\\]*$','\1','e')
    exe (a:right? "botright" : "topleft")." vertical ".((g:netrw_winsize > 0)? (g:netrw_winsize*winwidth(0))/100 : -g:netrw_winsize) . " new"
    if a:dir != ""
      exe "Explore ".a:dir
    else
      exe "Explore ".path
    endif
    setlocal winfixwidth
    let t:netrw_lexbufnr = bufnr("%")
  endif
endfun

Suggested options to behave like NERDTree:

" absolute width of netrw window
let g:netrw_winsize = -28

" do not display info on the top of window
let g:netrw_banner = 0

" tree-view
let g:netrw_liststyle = 3

" sort is affecting only: directories on the top, files below
let g:netrw_sort_sequence = '[\/]$,*'

" use the previous window to open file
let g:netrw_browse_split = 4

Toggle function

Here is my version of toggle function, based on Nick's answer. Now you can use hotkey from any pane, not only from netrw's pane. In Nick's version it causes an error, also I did some code cleanup and remap it to Ctrl-O, because Ctrl-E is used by default to scroll down by one line.

" Toggle Vexplore with Ctrl-O
function! ToggleVExplorer()
    if exists("t:expl_buf_num")
        let expl_win_num = bufwinnr(t:expl_buf_num)
        let cur_win_num = winnr()

        if expl_win_num != -1
            while expl_win_num != cur_win_num
                exec "wincmd w"
                let cur_win_num = winnr()
            endwhile

            close
        endif

        unlet t:expl_buf_num
    else
         Vexplore
         let t:expl_buf_num = bufnr("%")
    endif
endfunction

map <silent> <C-O> :call ToggleVExplorer()<CR>

Variable "t:expl_buf_num" is global for current tab, so you can have one Explorer per tab. You can change it to "w:expl_buf_num" if you want to be able to open Explorer in every window.

Keep focus in Explorer

Also I like to have this at my .vimrc:

" Open file, but keep focus in Explorer
autocmd filetype netrw nmap <c-a> <cr>:wincmd W<cr>

The 'Vexplore' command opens a vertical directory browser. You can build on this by adding the following code to your .vimrc file to toggle the vertical browser with Ctrl-E (for example):

" Toggle Vexplore with Ctrl-E
function! ToggleVExplorer()
  if exists("t:expl_buf_num")
      let expl_win_num = bufwinnr(t:expl_buf_num)
      if expl_win_num != -1
          let cur_win_nr = winnr()
          exec expl_win_num . 'wincmd w'
          close
          exec cur_win_nr . 'wincmd w'
          unlet t:expl_buf_num
      else
          unlet t:expl_buf_num
      endif
  else
      exec '1wincmd w'
      Vexplore
      let t:expl_buf_num = bufnr("%")
  endif
endfunction
map <silent> <C-E> :call ToggleVExplorer()<CR>

The code above tries to open the Explorer window on the left hand side of the screen at all times; I use it with multiple split vertical windows open.

[OPTIONAL] You might like to add the following lines to your .vimrc to improve the browsing experience:

" Hit enter in the file browser to open the selected
" file with :vsplit to the right of the browser.
let g:netrw_browse_split = 4
let g:netrw_altv = 1

" Change directory to the current buffer when opening files.
set autochdir