
To create two bridged virtual serial ports use the following command:
socat -d -d pty,raw,echo=0 pty,raw,echo=0
The output will show you which are the virtual ports (or pseudo terminals) created, e.g.:
2010/02/19 16:16:33 socat[9662] N PTY is /dev/pts/3
2010/02/19 16:16:33 socat[9662] N PTY is /dev/pts/4
2010/02/19 16:16:33 socat[9662] N starting data transfer loop with FDs [3,3] and [5,5]
Note: if you are using Ubuntu and you do not have this command, try:
sudo apt-get install socat