A command to close all Vim buffers that are not currently visible.

only.vim

command! -nargs=* Only call CloseHiddenBuffers()
function! CloseHiddenBuffers()
  " figure out which buffers are visible in any tab
  let visible = {}
  for t in range(1, tabpagenr('$'))
    for b in tabpagebuflist(t)
      let visible[b] = 1
    endfor
  endfor
  " close any buffer that are loaded and not visible
  let l:tally = 0
  for b in range(1, bufnr('$'))
    if bufloaded(b) && !has_key(visible, b)
      let l:tally += 1
      exe 'bw ' . b
    endif
  endfor
  echon "Deleted " . l:tally . " buffers"
endfun