[ns] how i setting environment variable?

[leon why]

Dear sir:
    i download some samples for ns-2 ,i want to run them .but i cannt 
setting environemt .how can i setting it
? i usually execute ns in /home/ns2/ns-allinone-2.27/ns-2.27 how can i 
execute these samples when i type ns command in this directory??  Be eager 
for your help!  Thanks a lot!!
                                                your sincerely
                                                     leon
                                                 04.05.02

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