tr(字符替换)

https://www.linuxprobe.com/tr-text-usage.html

• 大小写替换
  小写变大写
  echo "hello world，www.linuxidc.com" | tr "a-z" "A-Z"
  大写变小写
  echo "hello world，www.linuxidc.com" | tr "A-Z" "a-z"