bash-2.04$ perl -e '$x = 5; $y = "foo"; print ($y ? $x % $y : $x); print "\n"' Illegal modulus zero at -e line 1. bash-2.04$ perl -e '$x = 5; $y = "foo"; print ($y*1 ? $x % $y : 0); print "\n"' 0 bash-2.04$ perl -e '$x = 5; $y = "foo"; print (($y*1) ? $x % $y : $x); print "\n"' 5