Shell Programming and Scripting

#!/bin/sh
date1='Jul 15 2011 07:21:28'

date1_sec=$(date -d "$date1" '+%s')
date2_sec=$(date -d "$date1  5 min ago" '+%s')
while read line
do
        line_date=$(echo $line | awk '{print $1,$2,$3}')
        sec=$(date -d "$line_date" '+%s')
        if [ $date2_sec -le $sec -a $date1_sec -ge $sec ]
        then
                echo $line
        fi
done < /var/log/messages