$ nc -hOpenBSD netcat (Debian patchlevel 1.105-7ubuntu1)This is nc from the netcat-openbsd package. An alternative nc is availablein the netcat-traditional package.usage: nc [-46bCDdhjklnrStUuvZz] [-I length] [-i interval] [-O length]   [-P proxy_username] [-p source_port] [-q seconds] [-s source]   [-T toskeyword] [-V rtable] [-w timeout] [-X proxy_protocol]   [-x proxy_address[:port]] [destination] [port]  Command Summary:    -4    Use IPv4    -6    Use IPv6    -b    Allow broadcast    -C    Send CRLF as line-ending    -D    Enable the debug socket option    -d    Detach from stdin    -h    This help text    -I length  TCP receive buffer length    -i secs    Delay interval for lines sent, ports scanned    -j    Use jumbo frame    -k    Keep inbound sockets open for multiple connects    -l    Listen mode, for inbound connects    -n    Suppress name/port resolutions    -O length  TCP send buffer length    -P proxyuser  Username for proxy authentication    -p port    Specify local port for remote connects      -q secs    quit after EOF on stdin and delay of secs    -r    Randomize remote ports    -S    Enable the TCP MD5 signature option    -s addr    Local source address    -T toskeyword  Set IP Type of Service    -t    Answer TELNET negotiation    -U    Use UNIX domain socket    -u    UDP mode    -V rtable  Specify alternate routing table    -v    Verbose    -w secs    Timeout for connects and final net reads    -X proto  Proxy protocol: "4", "5" (SOCKS) or "connect"    -x addr[:port]  Specify proxy address and port    -Z    DCCP mode    -z    Zero-I/O mode [used for scanning]  Port numbers can be individual or ranges: lo-hi [inclusive]

$ nc -z -v -n 127.0.0.1 20-100...Connection to 127.0.0.1 80 port [tcp/*] succeeded!...

$ nc -l 192.168.1.11 1234 > passwd.txt &

$ nc 192.168.1.11 1234 < /etc/passwd

cat /etc/passwd | nc 192.168.1.11 1234