socat

TLDR

Forward TCP port to another host

$ socat TCP-LISTEN:[8080],fork TCP:[remote.host]:[80]

Create a simple TCP server

$ socat TCP-LISTEN:[1234],reuseaddr,fork EXEC:[/bin/cat]

Connect to a TCP port

$ socat - TCP:[host]:[port]

Forward Unix socket to TCP

$ socat TCP-LISTEN:[1234],fork UNIX-CONNECT:[/var/run/app.sock]

Create bidirectional pipe between processes

$ socat EXEC:'[command1]' EXEC:'[command2]'

Create a simple chat server

$ socat TCP-LISTEN:[12345],fork,reuseaddr STDOUT

SSL/TLS connection

$ socat - OPENSSL:[host]:[443],verify=0

Serial port to TCP

$ socat TCP-LISTEN:[5000] /dev/ttyUSB0,b9600,raw,echo=0

Create virtual terminal pair

$ socat -d -d pty,raw,echo=0 pty,raw,echo=0

SYNOPSIS

socat [options] address1 address2

socat (SOcket CAT) is a multipurpose relay tool that establishes two bidirectional byte streams and transfers data between them. It's like a more powerful netcat that supports numerous address types and protocols.
Address types include TCP, UDP, Unix sockets, files, pipes, PTYs, processes (EXEC), SSL, serial devices, and many more. socat can connect, listen, and relay between any combination of these.
Common use cases include port forwarding, protocol conversion, debugging network services, creating tunnels, and connecting disparate systems. It's invaluable for system administration and network troubleshooting.

PARAMETERS

TCP-LISTEN: port

Listen on TCP port.

TCP: host : port

Connect to TCP host:port.

UDP: host : port

UDP connection.

UNIX-CONNECT: path

Connect to Unix socket.

UNIX-LISTEN: path

Listen on Unix socket.

EXEC: command

Execute command and connect to its I/O.

OPENSSL: host : port

SSL/TLS connection.

PTY

Create pseudo-terminal.

STDIO or -

Standard input/output.

fork

Handle multiple connections.

reuseaddr

Allow address reuse.

verify= 0|1

SSL certificate verification.

-d -d

Verbose debugging output.

-v

Verbose data transfer logging.

CAVEATS

Complex address specifications require careful syntax. Fork option needed for multiple connections. SSL certificates may need configuration. Some features require elevated privileges.

HISTORY

socat was created by Gerhard Rieger in 1999 as an extended version of netcat with support for many more address types. It filled the need for a universal relay tool that could bridge different communication mechanisms. The project continues active maintenance and is widely used for network administration.