Communicating over TCP using bash

bash supports TCP connection using pseudo device files like /dev/tcp/<host>/<port>. Once you create a file descriptor and associate it with this device file, you can communicate over TCP just with bash.

# Open a new connection to www.google.com:80
# and associate it with file descriptor 3
exec 3<> /dev/tcp/www.google.com/80

# Send a request
cat >&3 << EOF
GET / HTTP/1.1
Host: www.google.com
Connection: close

EOF

# Read a response
cat <&3

# Close the file descriptor
exec 3>&-