#!/bin/bash
SAVEIFS=$IFS
IFS=$(echo -en "\n\b")

src="/volume1/homes/1605259395"
dst="/volume1/books"
echo $src
function read_dir() {
    for file in $(#
        ls $1
    ); do
        echo "-->"$file
        if [ -d $1"/"$file ]; then
            read_dir $1"/"$file
        elif [[ -f $1"/"$file && (${file: -4} == ".pdf" || ${file: -5} == ".epub" || ${file: -5} == ".azw3" || ${file: -5} == ".mobi") ]]; then # ｜｜cp base file to dst file
            echo $1$"/"$file
            [ $(mv -vn "$1""/""$file" $dst) ]
        else
            echo ".."
        fi
    done
}

read_dir $src
echo "successful!"
echo $1"  "$2
IFS=$SAVEIFS