怎么将文件改名为大写？

试图用mv命令将文件改名为大写时,返回不正常状态且文件没有被改名。如下：

ROOT$ touch a
ROOT$ mv a A
mv: ‘a’ and ‘A’ are the same file
ROOT$ echo $?
1
ROOT$ mv --version
mv (GNU coreutils) 8.23
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later http://gnu.org/licenses/gpl.html.
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There is NO WARRANTY, to the extent permitted by law.

Written by Mike Parker, David MacKenzie, and Jim Meyering.