#! /bin/sh
#
# $0 pattern1 pattern2

(echo "$1"; echo "$2") |
  awk 'NR==1 {
		p1 = $0;
		next;
	}
	NR==2 {
		p2 = $0;
		if (length(p1) != length(p2)) {
			print "Lengths differ";
		} else {
			d = 0;
			for (i=length(p1);i>0;i--) {
				if (substr(p1,i,1) != substr(p2,i,1)) {
					d ++;
				}
			}
			printf("%d\n",d);
		}
	}'