socat

socat, short for SOcket CAT, is a command-line utility that acts as a bidirectional data relay between two data streams. It is a general-purpose networking connector and tunnel, designed as a feature-rich successor to netcat (nc).

It supports a wide range of address types and protocols, enabling it to create listening and connecting endpoints and bridge between files, pipes, devices (for example, /dev/ttyS0), UNIX domain sockets, and network sockets. It supports IPv4 and IPv6, TCP, UDP, and SCTP, as well as SSL/TLS and proxies. It can fork for multiple connections, run as a daemon, perform chroot, and execute programs in response to connection events.

Usage examples: socat [options] <address1> <address2>. For instance, socat TCP4-LISTEN:1234,fork TCP4:host.example:5678 creates a listening server that forwards to host:5678. Another example is socat STDIO TCP4:host:80, which connects standard input/output to a remote port. The -d and -d -d options enable verbose logging; socat can also create tunnels, perform port forwarding, or bridge serial devices to network sockets.

Socat is primarily for Unix-like systems, with ports available for Linux, BSD, and macOS; Windows support exists but is less common. It is maintained as open-source software by a community of contributors and has a long-standing presence in networking toolkits.