You can also use the "constant" module:

use constant SCALAR_CONST => 3.14159265;
use constant ARRAY_CONST  => ( 'This', 'is', 'fun' );
use constant HASH_CONST   => ( pi => 3.14159265, 
                               c => 299_792_458 ); # m/s
#etc.
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Which actually just creates convenient sub routines for you. ( I prefer this method because it is a little more explicit, plus it is self documenting. )