split filename and move `abcdefgh.txt` -> `ab/cd/efgh.txt`.

splitter.sh

#!/usr/bin/env bash
# find input -type f -maxdepth 1 | parallel --load 100% ./splitter.sh input {}
input_dir=$1
f=$2
if [[ -f $f ]]
    then
    filename=$(basename $f)
    enclosing="${filename:0:1}/${filename:1:1}/"
    mkdir -p "$input_dir/$enclosing"
    mv $f "$input_dir/$enclosing$filename"
fi