Reverse Polish Calculator

A simple Perl command-line reverse polish calculator.

#!/usr/bin/perl

#Usage:
#~$ perl rpn.pl "(3 (3 20 *) +)"
#(3 (3 20 *) +) =
#63

$str = $ARGV[0];
$str =~ s/[\(\)]//g;
@expr = split(" ", $str);
@stack = ();

print $ARGV[0] . " = \n";

while($item = shift(@expr))
{
  if($item eq "+")
  {
    push(@stack, pop(@stack)+pop(@stack));    
  }
  elsif($item eq "-")
  {
    push(@stack, -pop(@stack)+pop(@stack));
  }
  elsif($item eq "*")
  {
    push(@stack, pop(@stack)*pop(@stack));
  }
  elsif($item eq "/")
  {
    push(@stack, 1/pop(@stack)*pop(@stack));
  }
  else
  {
    push(@stack, sprintf("%.3f",$item));
  }
}
print @stack;
print "\n";