How to set environment variable

[vikram vikram vikram]

  
Hi All,

        I am new to perl. I am using "Active Perl-5.8.8"  

         I want to set environment variable in a perl script 

                Ex - #!/usr/bin/perl
                      $ENV{HAI} = "hai";


                     and want to display the contents of the environment 
variable in the command line after executing the script.

          But it is not displaying the contents if i give 
                       echo $HAI

           Please help me out 

Thanks in advance 
Vikram