To append a serial number to all the files contained in a directory

filenameappender.sh

files=$(ls | awk '{print $1}')
serial=1
for fn in $files; do
    echo "the next file is $fn"
    extension="${fn##*.}"
	filename="${fn%.*}"
	echo "serial is $serial"
	echo "filename is $filename and extension is $extension"
	newfilename=$filename$serial
	echo "mv $filename.$extension $newfilename.$extension"
	mv $filename.$extension $newfilename.$extension
	echo "new filename is $newfilename"
	serial=$(($serial+1))
done