My svn server (Windows system) is VisualSVN, my svn client is TortoiseSVN.
I added bellow code in post-commit.cmd of VisualSVN.
echo (ignore "Error 99", which is a fake error, commit is already completed) SOME_OTHER_INFO 1>&2!
exit 99
Then it shows an info when I commit in svn client but I want the message not to show as an "error". How could I do this?

stderr. I guess that you could avoid that by writing intostdoutinstead.