cat /etc/issue

tr 'a-z' 'A-Z' < /etc/issue > /tmp/issue.out

cat /tmp/issue.out


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


cat /etc/issue | tr '[:lower:]' '[:upper:]' > /tmp/issue.out

cat /tmp/issue.out


将/etc/issue文件中的内容转换为大写后保存至/tmp/issue.out文件中_lower_02