As noted by Tux in Re^2: Global symbol requires explicit package... I also like the hash switch solution if there are more possibilities than one: 
my $lim = { linux =>  'clear',
            BASIC =>  'clrscr',
          }->{$^O} || 'cls';

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In reply to Re^3: Global symbol requires explicit package.. by choroba
in thread Global symbol requires explicit package.. by meanroc

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