Multiple commandlines accessing same instance of a program
 

I want to write a program that same instance of it can be accesed by multiple comandlines. What kind of a program it should be and how to write it?

You have to be more clear.

Any executable binary can be run as many times as you like by as many command line consoles as there are.

Multiple command line
 

yes , we can write multiple instances of a binary program using multple commandlines.
i want to run same instance of the program using multiple commandlines

"commandline" usually refers to a shell. And a shell is meant to run programs, not to access running programs. So, when using a shell, you'll have to use some kind of client-server architecture, similar to a ftp client, that accesses a ftp server.

"Sockets" are the basic level of interprocess-communication:
http://www.linuxhowtos.org/C_C++/socket.htm

There are higher levels of message buses, like "dbus".

A very low level of communication would be using the filesystem and file-content. Commands as simple as "echo" and "cat" could be enough to access your program.

A different approach would be to simply let your program open multiple windows/terminals. This depends on your needs.

Multiple commandline
 

I think I got the right answer. thank you very much @bluebox