multitee program
multitee and its documentation were
originally written
by Dan Bernstein.
multitee [ -bsize ] [ -vQq ] [ fd-fd,fd,fd... ] ...
multitee sends multiple inputs to multiple outputs. Given an
argument of the form “fdin-fdout,fdout,fdout...”, it
will send all input on file descriptor fdin to each descriptor
fdout. It will exit when all fdin are closed.
Several arguments may specify outputs from the same fdin.
-fdout and ,fdout are equivalent. If there is an
error of any sort (including SIGPIPE) in writing to
fdout, multitee prints a warning on stderr and
forgets fdout entirely. (This doesn't affect reads on
fdin.) If -fdout is replaced by
:fdout then multitee will exit upon any SIGPIPEs
from that descriptor.
Furthermore, efd means that as soon as
fdin reaches end of file, fd is considered to reach
EOF as well. multitee will warn about any input errors and then
treat them like EOF.
Unlike tee, multitee tries its best to continue
processing all descriptors even while some of them are blocked. However, it
will get stuck reading if another process is reading the descriptor and grabs
the input first; it will get stuck writing if an input packet does not fit in
an output pipe. (If the output descriptor has NDELAY set, and
multitee receives EWOULDBLOCK, it writes one byte
at a time to avoid pipe synchronization problems.) While it is tempting to
set the descriptors to non-blocking mode, this is dangerous: other processes
using the same open file may not be able to deal with NDELAY.
It is incredible that none of the major UNIX vendors or standards committees
has come up with true per-process non-blocking I/O. (Under BSD 4.3 and its
variants, multitee could send timer signals to itself rapidly to
interrupt any blocking I/O. However, this cannot work under BSD 4.2, and is
generally more trouble than it's worth.) A program can set
NDELAY before invoking multitee if it knows that no other
processes will use the same open file.
multitee will also temporarily stop reading an input descriptor
if more than 8192 bytes are pending on one of its output descriptors. This
does not affect independent fdin-fdout pairs.
multitee has several flags:
multitee, this version does not
require output buffers, and does not copy bytes anywhere
between read() and write().multitee will not use stderr in any way (except,
of course, if descriptor 2 is specified in an argument).multitee 0-1,4,5 4> foo 5> bar
Same as “tee foo bar” except for better
blocking behavior.
multitee 0:1 3:1 4:1,2 6:7
Merge several sources into the output, meanwhile copying 6 to 7 and recording 4's input in 2.
tcpclient servermachine smtp multitee 0:7 6:1e0
Same as mconnect on Suns. The e0 tells multitee to
quit as soon as the network connection closes.
multitee expects all descriptors involved to be open. Currently
a closed descriptor acts like an open descriptor which can never be written
to.