[ns] how to use shell script in tcl code and which place (in TCL script or not)

[S.M.Mehdi Feiz]

Hi all,
I want to simulate in different scenarios. I understand that i should use shell 
script, is this true or not??????? Furthemore, i should add this shell code in 
main tcl codeor not???? how to use this code in my tcl script.
Please, help me.
Thanks in Advance.
S.M.Mehdi Feiz