Write a buffer other than the current one?

[Efraim Yawitz]

I haven't been able to find a way to write a buffer other than the current one, i.e. something like a command :writebuf <bufnum> or a similar function.  It seems like this would be something useful to do, say after listing buffers and seeing which ones were changed.  I know one can do :wall, but that does not allow choosing which ones to save.

Thanks,

Ephraim