Ubuntu Manpage: multitee - send multiple inputs to multiple outputs

NAME

       multitee - send multiple inputs to multiple outputs

SYNTAX

       multitee [ -bsize ] [ -vQq ] [ fd-fd,fd,fd...  ] ...

DESCRIPTION

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 someone else 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:

-bsize Change input buffer size from 8192 to size. Unlike the previous version of multitee, this
version does not require output buffers, and does not copy bytes anywhere between read() and
write().

-v Verbose.

-q Quiet. multitee will not use stderr in any way (except, of course, if descriptor 2 is
specified in an argument).

-Q Normal level of verbosity.

EXIT VALUE

       0  normally.   1  for  usage  messages.   3  if  multitee  runs  out  of memory.  4 in various impossible
       situations.

DIAGNOSTICS

       fatal: out of memory
              multitee has run out of memory.

       warning: cannot read descriptor
              Self-explanatory.

       warning: cannot write descriptor
              Self-explanatory.

EXAMPLES

       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.

RESTRICTIONS

       multitee expects all descriptors involved to be open.  Currently a closed descriptor acts  like  an  open
       descriptor which can never be written to.

BUGS

       None known.

VERSION

       multitee version 3.0, 7/22/91.

AUTHOR

       Placed into the public domain by Daniel J. Bernstein.