I had never heard of this until I ran into working on a recent project. In “bash” you can open sockets:

exec file-descriptor<>/dev/tcp/IP-or-hostname-here/port

so for example:

exec 3<>/dev/tcp/192.168.1.100/23

would open port 23 (telnet) to IP “192.168.1.100″ for read and write (the “<>”) on file descriptor “3″ (remember descriptors 0, 1, and . . . → Read More: Bash TCP programming hack!?