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)