vim plugin for using numbered temp files

nextunused.vim

" ~/.vim/plugin/nextunused.vim

" find the next unused filename that matches the given pattern
" counting up from 0.  The pattern is used by printf(),
" so use 'temp%d.txt' for 'temp0.txt' to 'temp99999.txt' and
" 'temp%04d.txt' for 'temp0000.txt' to 'temp9999.txt'.
function! GetNextUnused( pattern )
  let i = 0
  while filereadable(printf(a:pattern,i))
    let i += 1
  endwhile
  return printf(a:pattern,i)
endfunction

" edit the next unused filename that matches the given pattern
command! -nargs=1 EditNextUnused :execute ':e ' . GetNextUnused('<args>')
" write the current buffer to the next unused filename that matches the given pattern
command! -nargs=1 WriteNextUnused :execute ':w ' . GetNextUnused('<args>')

" To use, try 
"   :EditNextUnused temp%d.txt
"
" or
"
"   :WriteNextUnused path/to/file%03d.extension
"