netcat

Connect to a host on a specific port

$ nc [host] [port]

$ nc -l [port]

$ nc -lk [port]

$ nc -zv [host] [20-30]

$ nc [host] [port] < [file.txt]

$ nc -l [port] > [received_file.txt]

$ nc -u [host] [port]

$ nc -w [5] [host] [port]

$ nc -6 [host] [port]

nc [options] [hostname] [port]
nc -l [options] [port]

nc (netcat) is a versatile networking utility for reading and writing data across TCP and UDP connections. Often called the "network Swiss army knife," it can create almost any kind of network connection and is invaluable for debugging and testing.
Common uses include: port scanning, transferring files, creating simple chat servers, network debugging, and testing network services. In listen mode (-l), nc waits for incoming connections; otherwise it initiates connections to remote hosts.
Data is read from stdin and written to stdout, making it easy to pipe data through network connections. Multiple implementations exist (OpenBSD, GNU, ncat from Nmap), with varying feature sets. The -e option for command execution exists in some versions but is omitted from security-focused implementations.

-l

Listen mode; wait for incoming connections

Keep listening after connection closes (with -l)

No DNS lookup; use numeric addresses only

Specify source port

Specify source IP address

Use UDP instead of TCP

Verbose output

Timeout for connections and idle time

Zero-I/O mode; scan without sending data

Force IPv4 only

Force IPv6 only

Do not read from stdin

Delay between lines sent/received

Randomize port numbers

Enable telnet negotiation

Send CRLF line endings

Connect via proxy

Proxy protocol (4=SOCKS4, 5=SOCKS5, connect=HTTPS)

Use Unix domain sockets

Execute command on connection (traditional nc only)

Different netcat implementations have different options and capabilities. OpenBSD netcat omits the -e flag for security reasons. Some options like -k may not be available in all versions. Port scanning may be detected as hostile activity. Use ncat (from Nmap) for consistent cross-platform behavior.

Netcat was originally written by a hacker known as Hobbit and released in 1995. It quickly became an essential tool for network administrators and security professionals. The original version included powerful but potentially dangerous features like -e for command execution. OpenBSD rewrote netcat from scratch in 2001 with a focus on security, removing risky features. The Nmap project created ncat as a modern reimplementation with SSL support and additional features.

ncat(1), socat(1), telnet(1), ss(8)