If for some strange reasons, the path to react-native is not in the PATH, you should take note where the react-native executable is installed. Generally, the issue with command not found is because they are not in PATH.

For example, I use nodenv and run npm install -g react-native

/Users/khoa/.nodenv/versions/10.10.0/bin/react-native -> /Users/khoa/.nodenv/versions/10.10.0/lib/node_modules/react-native/local-cli/wrong-react-native.js

So I need to add that to my PATH

export PATH=/Users/$HOME/.nodenv/versions/10.10.0/bin:$PATH

You can verify with echo $PATH

Or you can use npx to execute local npm modules, for example

npx react-native run-ios --simulator='iPhone X'

If for some strange reasons, the path to react-native is not in the PATH, you should take note where the react-native executable is installed. Generally, the issue with command not found is because they are not in PATH.

For example, I use nodenv and run npm install -g react-native

/Users/khoa/.nodenv/versions/10.10.0/bin/react-native -> /Users/khoa/.nodenv/versions/10.10.0/lib/node_modules/react-native/local-cli/wrong-react-native.js

So I need to add that to my PATH

export PATH=$HOME/.nodenv/versions/10.10.0/bin:$PATH

You can verify with echo $PATH

Or you can use npx to execute local npm modules, for example

npx react-native run-ios --simulator='iPhone X'