I need a shell script for the following logic. Can anyone pls. help me?

1. Read a file <x.dat> having some data
2. Check if the output file <y.dat> exists and has data
3. If <y.dat> exists then append data to <y.dat>
4. Else create new <y.dat>

Datafile: x.dat
10:00 Batch run1.exe
11:00 Batch run2.exe
12:00 Batch run3.exe

Datafile y.dat (if exists)
05:00 Batch run99.exe
04:00 Batch run98.exe

Thanks and Regards.,
Aravind

Try this
terminal=`tty`
exec < x.dat
while read line
do
if [ -z y.dat ]
then
echo $line >>y.dat
else
echo $line >y.dat
fi
done

exec <$terminal