creates a process that uses
to stream data in chunks of at most
or 8192 bytes) from
to the standard output.
the two files are instead cross-connected by two streaming processes:
one process streams data from
and the other streams data from
In all cases,
writes data to the destination file in full buffers of
waits for all streaming processes to stop before returning,
(asynchronous) option is given, which causes it to
return after spawning the streamers.