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分类: LINUX

2010-11-04 17:39:59

NAME
       nc - TCP/IP swiss army knife

SYNOPSIS
       nc [-options] hostname port[s] [ports] ...
       nc -l -p port [-options] [hostname] [port]

DESCRIPTION
       netcat is a simple unix utility which reads and writes data across network connections, using TCP or UDP protocol. It is designed to be a reliable "back-
       end" tool that can be used directly or easily driven by other programs and scripts.  At the same time, it is a feature-rich network debugging and  explo‐
       ration  tool, since it can create almost any kind of connection you would need and has several interesting built-in capabilities.  Netcat, or "nc" as the
       actual program is named, should have been supplied long ago as another one of those cryptic but standard Unix tools.

       In the simplest usage, "nc host port" creates a TCP connection to the given port on the given target host.  Your standard input is then sent to the host,
       and  anything  that comes back across the connection is sent to your standard output.  This continues indefinitely, until the network side of the connec‐
       tion shuts down.  Note that this behavior is different from most other applications which shut everything down and exit after an end-of-file on the stan‐
       dard input.

       Netcat  can  also  function as a server, by listening for inbound connections on arbitrary ports and then doing the same reading and writing.  With minor
       limitations, netcat doesn’t really care if it runs in "client" or "server" mode -- it still shovels data back and forth until there isn’t any more  left.
       In either mode, shutdown can be forced after a configurable time of inactivity on the network side.

       And it can do this via UDP too, so netcat is possibly the "udp telnet-like" application you always wanted for testing your UDP-mode servers.  UDP, as the
       "U" implies, gives less reliable data transmission than TCP connections and some systems may have trouble sending large amounts of  data  that  way,  but
       it’s still a useful capability to have.

       You  may  be  asking  "why not just use telnet to connect to arbitrary ports?" Valid question, and here are some reasons.  Telnet has the "standard input
       EOF" problem, so one must introduce calculated delays in driving scripts to allow network output to finish.  This is the main reason netcat stays running
       until  the  *network* side closes.  Telnet also will not transfer arbitrary binary data, because certain characters are interpreted as telnet options and
       are thus removed from the data stream.  Telnet also emits some of its diagnostic messages to standard output, where netcat keeps such things  religiously
       separated  from  its *output* and will never modify any of the real data in transit unless you *really* want it to.  And of course telnet is incapable of
       listening for inbound connections, or using UDP instead.  Netcat doesn’t have any of these limitations, is much smaller and faster than telnet,  and  has
       many other advantages.

OPTIONS
       -c string    specify  shell  commands  to exec after connect (use with caution).  The string is passed to /bin/sh -c for execution.  See the -e option if
                    you don’t have a working /bin/sh (Note that POSIX-conformant system must have one).

       -e filename  specify filename to exec after connect (use with caution).  See the -c option for enhanced functionality.

       -g gateway   source-routing hop point[s], up to 8

       -G num       source-routing pointer: 4, 8, 12, ...

       -h           display help

       -i secs      delay interval for lines sent, ports scanned

       -l           listen mode, for inbound connects

       -n           numeric-only IP addresses, no DNS

       -o file      hex dump of traffic

       -p port      local port number (port numbers can be individual or ranges: lo-hi [inclusive])

       -q seconds   after EOF on stdin, wait the specified number of seconds and then quit. If seconds is negative, wait forever.

       -b           allow UDP broadcasts

       -r           randomize local and remote ports

       -s addr      local source address

       -t           enable telnet negotiation

       -u           UDP mode

       -v           verbose [use twice to be more verbose]

       -w secs      timeout for connects and final net reads

       -z           zero-I/O mode [used for scanning]

       -T type      set TOS flag (type may be one of "Minimize-Delay", "Maximize-Throughput", "Maximize-Reliability", or "Minimize-Cost".)

COPYRIGHT
       Netcat is entirely my own creation, although plenty of other code was used as examples.  It is freely given away to the Internet community  in  the  hope
       that  it  will  be  useful, with no restrictions except giving credit where it is due.  No GPLs, Berkeley copyrights or any of that nonsense.  The author
       assumes NO responsibility for how anyone uses it.  If netcat makes you rich somehow and you’re feeling generous, mail me a check.  If you are  affiliated
       in any way with Microsoft Network, get a life.  Always ski in control.  Comments, questions, and patches to hobbit@avian.org.

NOTES
       Some  port names in /etc/services contain hyphens -- netcat currently will not correctly parse those unless you escape the hyphens with backslashes (e.g.
       "netcat localhost ’ftp\-data’").

BUGS
       Efforts have been made to have netcat "do the right thing" in all its various modes.  If you believe that it is doing the wrong thing under whatever cir‐
       cumstances,  please  notify  me and tell me how you think it should behave.  If netcat is not able to do some task you think up, minor tweaks to the code
       will probably fix that.  It provides a basic and easily-modified template for writing other network applications, and I  certainly  encourage  people  to
       make custom mods and send in any improvements they make to it. Continued feedback from the Internet community is always welcome!

EXAMPLES
       For several netcat recipes, please see /usr/share/doc/netcat/README.gz and /usr/share/doc/netcat/README.Debian.gz.

AUTHOR
       This manual page was written by Joey Hess and Robert Woodcock , cribbing heavily from Netcat’s README file.

       Netcat was written by a guy we know as the Hobbit .
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