Back at the start of April I wrote mysql2 ruby gem and Mac OS X: image not found to deal with the extremely relative path to libmysqlclient.16.dylib. I had said I would prefer not putting libmysqlclient.16.dylib in /usr/lib but I couldn't find a dylib path that ruby uses. That is until today when I decided to try again.
I found libexecdir in RbConfig::CONFIG which is the directory where ruby can load dylib files from.
libexecdir=$(ruby -rrbconfig -e 'puts RbConfig::CONFIG["libexecdir"]')
sudo mkdir -p $libexecdir
sudo ln -s /usr/local/mysql/lib/libmysqlclient.16.dylib $libexecdirNow ruby can load libmysqlclient.16.dylib without putting it in /usr/lib.
I forgot to mention it in the first post but if your ruby wants libmysqlclient.18.dylib, just replace the 16 with 18. Same with any other number.