Shell Programming and Scripting

users=`cat /etc/passwd | cut -d: -f1`
for i in $users
do
isloggedin=`who | grep $i | head -1`
if [ -n isloggedin ]
then
echo $isloggedin
else
echo $users
fi
done

users=`cat /etc/passwd | cut -d: -f1`
for i in $users
do
  isloggedin=`who | grep $i | head -1`
  if [ -n $isloggedin ]
    then
      echo $isloggedin
    else
      echo $users
  fi
done

awk 'BEGIN{while("who" | getline)w[$1]}
$1 in w {print $1 " is logged in"; next}
{print $1 " is NOT logged in"}
' FS=":" /etc/passwd