How can I send all writable buffers to an external command? For example,
:wa ! wc -l
does not work (gives trailing characters error). (Also, wa will not work anyway because it does not write unchanged buffers).
It needs to be writable buffers because I may have buffers like help open that are not writable that I do not want to include.
BTW, bufdo does not work, both because it includes read only buffers and because it executes the commands separately and therefore hangs the interface.