【实证】

第一步：文件名及扩展名转换为大写

参考：http://blog.chinaunix.net/uid-24426415-id-77492.html

#!/bin/bash
dir="./";    
files=`find $dir -type f`;
for i in $files  
do
dir_name=`dirname $i`;
ori_filename=`basename $i`;
new_filename=`echo $ori_filename | tr [:lower:] [:upper:]`>/dev/null;    
mv -f $dir_name/$ori_filename $dir_name/$new_filename
done

第二步：把扩展名转换为小写

参考：https://blog.csdn.net/longxibendi/article/details/6387732

find ./ -name "*.PHP" | awk -F "." '{print $2}' | xargs -i -t mv ./{}.PHP  ./{}.php

【参考】

参考：https://blog.chaos.run/dreams/linux-rename-all-files-in-a-directory-to-uppercase/index.html
参考：https://blog.csdn.net/tuzhg/article/details/81455924
参考：https://blog.csdn.net/qq_36792209/article/details/82695477

for f in *; do mv "$f" "${f^^}"; done

for f in *; do mv "$f" "$(echo "$f" | tr '[:lower:]' '[:upper:]')"; done

#!/bin/bash
for fileName in `ls test`
do
lowercase=`echo $fileName | tr '[A-Z]'  '[a-z]'`
echo $lowercase
mv test/$fileName test/$lowercase
done
echo success