factorial shell script

#!/bin/sh

function factorial()

{

N=$1

A=1

while test $N -gt 0 ; do

A = `expr $A '*' $N`

N = `expr $N - 1`

done

echo $A

}



factorial



It is giving me a message that unary operator is expected at line 6 which is

while test $N - gt 0 ; do