将/etc/issue文件中的内容转换为大写后保存至/tmp/issue.out文件中

[root@centos8 etc]# tr 'a-z' 'A-Z' < /etc/issue > /tmp/issue.out	#大小写转换
[root@centos8 etc]# cat /tmp/issue.out 	#源文件
\S
KERNEL \R ON AN \M

[root@centos8 etc]# cat  /etc/issue	#目标文件
\S
Kernel \r on an \m