Passes -w, but not strict. No error checking, but it works for the 4 major functions. 102 strokes, not counting the shebang line.

Is there a better (shorter) way to do the $y=o;$x=o; $x$1$y part? You have to do it in that order or else division and subtraction give the wrong result, but it seems like that could be condensed further.

#!/usr/bin/perl -w sub p{push@s,shift}sub o{pop@s}for$n(@ARGV){if($n=~/(\D)/){$y=o;$x=o;p +(eval"$x$1$y")}else{p$n}}print o

A fair fight is a sign of poor planning.