If you have a directory with lots of files in it, this POSIX compliant Bash script is here to help you to move its files into subdirectories.

#!/usr/bin/env bash

echo "$(find . -type f | wc -l)" files

printf "How many subdirectories: "
read -r F
printf "Subdirectories prefix: "
read -r S

PARENT=${PWD}
n=0
for i in *
do
  if [ $((n+=1)) -gt "$F" ]; then
    n=1
  fi
  todir=$PARENT/"$S"_$n
  [ -d "$todir" ] || mkdir "$todir" 
  mv "$i" "$todir" 
done