You can try something like that :
Code:
filename=c15a
datestamp=$(date +%Y%m%d)
last_file=$(ls -1 $filename.$datestamp.* 2>/dev/null | tail -1)
if [ -z "$last_file" ]
then
number=1
else
number=$(( ${last_file##*.} + 1 ))
fi
new_filename=$(printf "%s.%s.%05.5d" "$filename" "$datestamp" "$number")
mv $filename $new_filename
