while : ; do
ls -1rt abc[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9].txt > /dev/null
if [ $? -eq 0 ] ;then
lastfile=`ls -1rt abc[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9].txt|tail -1`
cp $lastfile backup/
mv $lastfile abc.txt
run your set of commands here
else
exit
fi
done