if ($ARGV[0]=="tri") {
   my $figure="triangle";
 }
 elsif ($ARGV[0]=="cir") {
   my $figure="circle";
 }
 ...

 if ($ARGV[1]=="area") {
   my $op="area";
   if ($figure=="rectangle") { my $reqargs=2; }
   elsif ($figure=="square") { my $reqargs=1;}
   elsif ($figure=="triangle") { my $reqargs=2; }
   elsif ($figure=="circle") { my $reqargs=1; }
 }