for dir in /home/*; do

....

done

passwords=$(cat /etc/passwd)  # I'm always looking for excuses to use arrays in bash
for (( entry=0; entry<${#passwords[@]}; entry++ )); do
   uid=$(echo ${passwords[$entry]} | cut -d':' -f1)
   if [ $uid -ge 500 -a $uid -lt 2000 ]; then  # regular users have uids between 500 and 2000 inclusively.
      echo $(echo ${passwords[$entry]} | cut -d':' -f3) >reguserlist
   fi   # add user to list if in range.
done

for username in $(cat reguserlist);do

...

done
rm reguserlist

Username         Port     From             Latest
root             tty1                      Thu Jan 25 15:23:50 +0530 2007
daemon                                     **Never logged in**
bin                                        **Never logged in**
sys                                        **Never logged in**
sync                                       **Never logged in**
vivek            tty1                      Sat Jan 27 22:10:36 +0530 2007
pdnsd                                      **Never logged in**
sshd                                       **Never logged in**
messagebus                                 **Never logged in**
bind                                       **Never logged in**

for dir in /home/*; do

....

done

#!/bin/sh
OLDMASK=`umask`
TIMESTAMP=`date +%s`
FILENAME=/tmp/accounting
TMPFILE=/tmp/accounting.new
EXPIRED=/tmp/expired.accounts

# This is the number of seconds until the account is out of date:
# 7776000 = 90 days
SECONDS=7776000

umask 077

if [ ! -f ${FILENAME} ]; then
        touch ${FILENAME}
fi

#lastlog | awk '{print $1}' | while read LINE
lastlog | grep "`date | awk '{print $2, $3".*"$6}'`" | awk '{print $1}' | while read LINE
do
        awk -v time=${TIMESTAMP} -v user="${LINE}" 'BEGIN{found=0}{if($2 == user){$1=time;found=1};print $0}END{if(found!=1){print time" "user}}' ${FILENAME} > ${TMPFILE}
        mv ${TMPFILE} ${FILENAME}
done

sort -n ${FILENAME} > ${TMPFILE}
mv ${TMPFILE} ${FILENAME}

awk -v time=${TIMESTAMP} -v secs=${SECONDS} 'BEGIN{old=time-secs}{if($1<=old)print $2}' ${FILENAME} >> ${EXPIRED}

umask ${OLDMASK}