BASH better way to monitor files - bash

Question

I've made a Bash script to monitor some server log files for certain data and my method probably isn't the most efficient.
One section specifically bugs me is that I have to write a newline to the monitored log so that the same line wont be read over continually.
Feedback would be greatly appreciated!
#!/bin/bash
serverlog=/home/skay/NewWorld/server.log
onlinefile=/home/skay/website/log/online.log
offlinefile=/home/skay/website/log/offline.log
index=0
# Creating the file
if [ ! -f "$onlinefile" ]; then
touch $onlinefile
echo "Name Date Time" >> "$onlinefile"
fi
if [ ! -f "$offlinefile" ]; then
touch $offlinefile
echo "Name Date Time" >> "$offlinefile"
fi
# Functions
function readfile {
# Login Variables
loginplayer=`tail -1 $serverlog | grep "[INFO]" | grep "joined the game" | awk '{print $4}'`
logintime=`tail -1 $serverlog | grep "[INFO]" | grep "joined the game" | awk '{print $2}'`
logindate=`tail -1 $serverlog | grep "[INFO]" | grep "joined the game" | awk '{print $1}'`
# Logout Variables
logoutplayer=`tail -1 $serverlog | grep "[INFO]" | grep "left the game" | awk '{print $4}'`
logouttime=`tail -1 $serverlog | grep "[INFO]" | grep "left the game" | awk '{print $2}'`
logoutdate=`tail -1 $serverlog | grep "[INFO]" | grep "left the game" | awk '{print $1}'`
# Check for Player Login
if [ ! -z "$loginplayer" ]; then
echo "$loginplayer $logindate $logintime" >> "$onlinefile"
echo "Player $loginplayer login detected" >> "$serverlog"
line=`grep -rne "$loginplayer" $offlinefile | cut -d':' -f1`
if [ "$line" > 1 ]; then
sed -i "$line"d $offlinefile
unset loginplayer
unset line
fi
fi
# Check for Player Logout
if [ ! -z "$logoutplayer" ]; then
echo "$logoutplayer $logoutdate $logouttime" >> "$offlinefile"
echo "Player $loginplayer logout detected" >> "$serverlog"
line=`grep -rne "$logoutplayer" $onlinefile | cut -d':' -f1`
if [ "$line" > 1 ]; then
sed -i "$line"d $onlinefile
unset logoutplayer
unset line
fi
fi
}
# Loop
while [ $index -lt 100 ]; do
readfile
done
Thanks!

Answer 1

instead of using multiple
tail -n 1 file
try the following construct:
tail -f file | while read line;do
echo "read: $line"
done
it will be much more reliable...and won't read the same line twice ;)
note: by using new processes of grep/awk/etc you are burning away processes...it's not that it is critical, but usually process creation is expensive...but if new lines occur rarely it's perfectly fine
where i want'ed to get is: if you are intrested, take a look at bash builting string manipulator function replace $(x/aa} ${x//aa} and friends..or try to use extended regexpes with grep