#!/bin/bash

target='lsd.log'

while IFS= read -d $'\0' -r file ; do
    file_list=("${file_list[@]}" "$file")
done < <( find -name "*.txt" -print0)

for file in "${file_list[@]}"
do
    cat $file >> $target
done

wc $target
tail -n 100 $target