While developing React Native apps (or Ionic Framework) I really dislike opening Android Studio on my Mac just to launch an emulator.

To avoid this, I use this workflow:

# Put this in your `~/.bash_profile`

export ANDROID_HOME=/Users/YOUR_USER_DIRECTORY_HERE/Library/Android/sdk

# NOTE: To use this right away in the same terminal or any currently open terminal, you'll need to source it:

> source ~/.bash_profile

# Now, see what emulators you have:

> $ANDROID_HOME/emulator/emulator -list-avds

# You'll get a list like this:

Pixel_XL_API_28
Pixel_XL_API_27

# Now launch one of the emulators

> nohup $ANDROID_HOME/emulator/emulator -avd Pixel_XL_API_28 &>/dev/null &

That's all it takes to get an Android emulator up and running in a few seconds.