Shell Programming and Scripting

if who | cut -f1 -d " " | uniq -d | grep -xf user.deny ; then
    echo
    echo "$(cat /etc/passwd | awk -F: '{print $5}') has logged in more than once"
else
    echo
    echo "None found"
fi

users=`who | cut -f1 -d " " | uniq -d | fgrep -xf user.deny`
case $? in
  0) for f in $users; do
      echo "s/^$f"':[^:]*:[^:]*:[^:]*:\([^:,]*\)[:,].*/\1 has logged in more than once/p'
    done | sed -n -f - /etc/passwd
  *) echo None found ;;
esac

echo "s/^$f"':[^:]*:[^:]*:[^:]*:\([^:,]*\)[:,].*/\1 has logged in more than once/p'

awk -v regex=^`echo -n "$users"*| tr ' ' '|'`$ -F : '
  $1 ~ regex { p=$5; sub (/,.*/, "", p); print p " has logged in more than once" }' /etc/passwd