#!/bin/sh 

grep=""
cmdline=""

if [ $# -ge 1 -a ${1-blah} = "-a" ]; then
   cmdline="-a"
   shift
fi

if [ $# -ge 1 ]; then
   grep="("
   while [ $# -ge 1 ]; do
     grep="${grep}^$1[^a-z]"
     shift
     if [ $# -ge 1 ]; then
        grep="${grep}|"
     fi
   done
   grep="${grep})"
   rwho ${cmdline} | egrep ${grep}
else
   rwho ${cmdline}
fi