add netcat manpage
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Mike Frysinger
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.TH NC 1
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.SH NAME
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nc \- TCP/IP swiss army knife
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.SH SYNOPSIS
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.B nc
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.I "[-options] hostname port[s] [ports] ..."
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.br
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.B nc
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.I "-l -p port [-options] [hostname] [port]"
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.SH "DESCRIPTION"
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.nf
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\fBnetcat\fR is a simple unix utility which reads and /\\_/\\
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writes data across network connections, using TCP / 0 0 \\
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or UDP protocol. It is designed to be a reliable ====v====
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"back-end" tool that can be used directly or easily \\ W /
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driven by other programs and scripts. At the same | | _
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time, it is a feature-rich network debugging and / ___ \\ /
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exploration tool, since it can create almost any / / \\ \\ |
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kind of connection you would need and has several (((-----)))-'
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interesting built-in capabilities. Netcat, or "nc" /
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as the actual program is named, should have been ( ___
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supplied long ago as another one of those cryptic \\__.=|___E
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but standard Unix tools. /
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.fi
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.P
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In the simplest usage, "nc host port" creates a TCP connection to the
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given port on the given target host. Your standard input is then sent
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to the host, and anything that comes back across the connection is
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sent to your standard output. This continues indefinitely, until the
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network side of the connection shuts down. Note that this behavior is
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different from most other applications which shut everything down and
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exit after an end-of-file on the standard input.
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.P
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Netcat can also function as a server, by listening for inbound
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connections on arbitrary ports and then doing the same reading and
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writing. With minor limitations, netcat doesn't really care if it
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runs in "client" or "server" mode -- it still shovels data back and
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forth until there isn't any more left. In either mode, shutdown can be
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forced after a configurable time of inactivity on the network side.
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.P
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And it can do this via UDP too, so netcat is possibly the "udp
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telnet-like" application you always wanted for testing your UDP-mode
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servers. UDP, as the "U" implies, gives less reliable data
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transmission than TCP connections and some systems may have trouble
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sending large amounts of data that way, but it's still a useful
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capability to have.
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.P
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You may be asking "why not just use telnet to connect to arbitrary
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ports?" Valid question, and here are some reasons. Telnet has the
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"standard input EOF" problem, so one must introduce calculated delays
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in driving scripts to allow network output to finish. This is the
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main reason netcat stays running until the *network* side closes.
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Telnet also will not transfer arbitrary binary data, because certain
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characters are interpreted as telnet options and are thus removed from
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the data stream. Telnet also emits some of its diagnostic messages to
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standard output, where netcat keeps such things religiously separated
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from its *output* and will never modify any of the real data in
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transit unless you *really* want it to. And of course telnet is
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incapable of listening for inbound connections, or using UDP instead.
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Netcat doesn't have any of these limitations, is much smaller and
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faster than telnet, and has many other advantages.
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.SH OPTIONS
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.TP 13
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.BR -4
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use of IPv4 addresses (also the default)
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.TP 13
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.BR -6
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use of IPv6 addresses
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.TP 13
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.BR -b
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allow broadcast addresses
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.TP 13
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.BR \-c " string"
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specify shell commands to exec after connect (use with caution). The string is
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passed to /bin/sh \-c for execution. See the
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.BR \-e
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option if you don't have a working /bin/sh (Note that POSIX-conformant system
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must have one).
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.TP 13
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.BR \-e " filename"
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specify filename to exec after connect (use with caution). See the
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.BR \-c
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option for enhanced functionality.
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.TP 13
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.BR \-g " gateway"
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source-routing hop point[s], up to 8
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.TP 13
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.BR \-G " num"
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source-routing pointer: 4, 8, 12, ...
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.TP 13
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.BR \-h
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display help
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.TP 13
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.BR \-i " secs"
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delay interval for lines sent, ports scanned
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.TP 13
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.BR \-l
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listen mode, for inbound connects
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.TP 13
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.BR \-n
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numeric-only IP addresses, no DNS
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.TP 13
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.BR \-o " file"
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hex dump of traffic
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.TP 13
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.BR \-p " port"
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local port number (port numbers can be individual or ranges: lo-hi
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[inclusive])
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.TP 13
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.BR \-q " seconds"
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after EOF is detected, wait the specified number of seconds and then
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quit.
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.TP 13
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.BR \-r
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randomize local and remote ports
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.TP 13
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.BR \-s " addr"
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local source address
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.TP 13
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.BR \-t
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enable telnet negotiation
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.TP 13
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.BR \-u
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UDP mode
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.TP 13
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.BR \-v
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verbose [use twice to be more verbose]
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.TP 13
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.BR \-w " secs"
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timeout for connects and final net reads
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.TP 13
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.BR \-z
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zero-I/O mode [used for scanning]
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.SH COPYRIGHT
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Netcat is entirely my own creation, although plenty of other code was
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used as examples. It is freely given away to the Internet community
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in the hope that it will be useful, with no restrictions except giving
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credit where it is due. No GPLs, Berkeley copyrights or any of that
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nonsense. The author assumes NO responsibility for how anyone uses
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it. If netcat makes you rich somehow and you're feeling generous,
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mail me a check. If you are affiliated in any way with Microsoft
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Network, get a life. Always ski in control. Comments, questions, and
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patches to hobbit@avian.org.
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.SH NOTES
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Some port names in /etc/services contain hyphens -- netcat assumes dashes
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are only used for ranges, so you have to escape the hyphens with backslashes
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(e.g. "netcat localhost 'ftp\\\-data'") to use them.
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.SH BUGS
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Efforts have been made to have netcat "do the right thing" in all its
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various modes. If you believe that it is doing the wrong thing under
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whatever circumstances, please notify me and tell me how you think it
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should behave. If netcat is not able to do some task you think up,
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minor tweaks to the code will probably fix that. It provides a basic
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and easily-modified template for writing other network applications,
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and I certainly encourage people to make custom mods and send in any
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improvements they make to it. Continued feedback from the Internet
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community is always welcome!
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.SH "SEE ALSO"
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/usr/share/doc/netcat/README.gz
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.SH AUTHOR
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This manual page was written by Joey Hess <joeyh@debian.org> and
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Robert Woodcock <rcw@debian.org>, cribbing heavily from Netcat's
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README file.
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.P
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Netcat was written by a guy we know as the Hobbit <hobbit@avian.org>.
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