my $shape = shift @ARGV;     # take first argument off ARGV
my $op = shift @ARGV;        # take second argument off ARGV
my %shapes = (
        "tri" => {
                name => "triangle",
                area => 2,   # required number of args
                peri => 3,
                hypo => 2,
        },
        "sqr" => {
                name => "square",
                area => 1,
                peri => 1,
        },
        "rec" => {
                name => "rectangle",
                area => 2,
                peri => 2,
        },
        "cir" => {
                name => "circle",
                area => 1,
                peri => 1,
        },
);
# Get full name of figure.
my $figure = $shapes{$shape}{name} or die "Unknown shape: $shape\n";

# Determine how many arguments we require.
my $reqargs = $shapes{$shape}{$op} or die "Unknown operator $op".
                " or $op does not work with shape $figure";