Shell script traverses files in a directory

Shell script to traverse all txt files in a directory:

#!/bin/bash
TODAY=`date +"%Y%m%d"`;
BACKUP_DIR=/opt/backup/$TODAY;

echo $TODAY;
echo "=====第一种方法====="
for table in $BACKUP_DIR/*.txt; 
do
	echo $table
done

echo "=====第二种方法====="
dir=`ls $BACKUP_DIR/*.txt` 
for table in $dir
do 
	echo $table
done

result:

[root@VM_0_6_centos opt]# ./test.sh
20200318
=====第一种方法=====
/opt/backup/20200318/1.txt
/opt/backup/20200318/2.txt
=====第二种方法=====
/opt/backup/20200318/1.txt
/opt/backup/20200318/2.txt