Other "git log" does not work for multiple author filtering

I used git 2.9.2 on FreeBSD 11, and I want to search the log for two authors, the command is like git log --author="Andrew\|Stephen". But it does not give any output. If I use two commands to search Andrew and Stephen, both of them work fine.
I also run this command on Ubuntu, it works. So, it looks like the regex used by git for FreeBSD is different from the one used on Linux. How can I make it work?
I found the answer through Internet. I need to use extended regex by git config --global grep.extendedRegexp true. Then I can use git log --author="Andrew|Stephen" --since="2016-09-20"