Hello sir.
I could establish the connection between any 2 systems in LAN using Socket Class in Java. I would like to learn more and know how to connect to other users in the LAN and send the messages using the shell instead of java..........

UNIX/Linux shells usually do not have native support for socket programming (although bash and some versions of ksh do, mostly on Linux).

You could try to use netcat, as it can work both as a server and a client and supports piping to/from other programs/file descriptors.

Never used it myself but I understand from the man page that ksh93 has built-in support
for direct socket access provided your platform supports sockets in the form /dev/tcp
/hostid/portid and /dev/udp/hostid/portid where hostid is the dotted decimal number of
the host and portid is the port the server is listening on.