Thanks for any help in advance , I am new to Mac in general so please forgive my question if its very straightforward, I installed native-react-cli and wanted to open/create
I had this issue, and it was simply due to my brew not being up to date.
I updated brew and re-installed the components listed at https://facebook.github.io/react-native/docs/getting-started.html#content and it was happy again.
you have to add right path to your path variable.
check this: react-native: command not found