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.
SEE ALSO
tee(1)
multitee(1)