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if (defined $ARGV[0] && defined $ARGV[1] && defined $ARGV[2] && define
+d $ARGV[3]) {
        ...
...
else {  #Die if less than 4 args given
        die "Please define at least 4 arguments\n"; 
}

if(@ARGV < 4) {
    die "Please define at least 4 arguments\n";
}
# I must have 4 arguments at this point.

 if ($ARGV[0]=="tri") {
   my $figure="triangle";
...
   elsif ($figure=="triangle") { my $reqargs=2; }
   elsif ($figure=="circle") { my $reqargs=1; }
 }

   my $shape = shift @ARGV;   # take first argument off ARGV
   my %shapes = ( 
...
                "sqr" => "square"
              );
   my $figure = $shapes{$shape} or die "Unknown shape $shape\n";

my $shape = shift @ARGV;     # take first argument off ARGV
my $op = shift @ARGV;        # take second argument off ARGV
...
my $reqargs = $shapes{$shape}{$op} or die "Unknown operator $op".
                " or $op does not work with shape $figure";

  elsif ($refsum==12.2) {
   my $diameter=$ARGV[3];
   my $answer=$diameter*$pi;
 }                           # $answer stops existing HERE

  elsif ($refsum==12.2) {
   my $diameter=$ARGV[3];
   $answer=$diameter*$pi;
 }

#!usr/bin/perl -w
use warnings;
...
              "Unknown.\n";
}
print "pi is $pi\n";