First Tcl script for beginners: "Hello World"

Hope you all have installed ns2 , now we can go for coding
As the ns2 simulations work on tcl scripts so we should know about tcl
Here some simple steps to write the "hello world" program in tcl

we can write tcl codes in two ways in interactive mode and in batch mode

first we can have look to interactive mode 

1.open the terminal
             type  $ ns
2. a command prompt open
         Create a new simulator object by using the command

                        set ns [ new Simulator ]

This is Usually the first non-comment statement in ns-2 script 
- Initialize the packet format

   - Create a scheduler (default is a calendar scheduler)

   - Create a “null agent”

3.  to print text on screen we use puts command
               $ns at 1 "puts "\Hello World\""

    here we Schedule an event to write at the time 1 

      by this script simulator instance "ns" writes "hello World"

4.  now we have to exit the simulator object
                         $ns at 1.5 "exit"

 5. now we have to run the simulator object,
                      $ns run
this starts ns

           
and this prints hello world

In batch mode  its much simple

open a text editor and write the codes there and save it with .tcl  file extention 

 expamlpe

 hello.tcl :

set ns [new Simulator]
$ns at 1 "puts \"hello world\""
$ns at 1.5 "exit"
$ns run

open the terminal and execute the hello.tcl by
            $ ns hello.tcl