Step 1 ( Add Environment Variable )
 export ANDROID_HOME=/Users/$(whoami)/Library/Android/sdk
 export PATH=$PATH:$ANDROID_HOME/platform-tools
 export PATH=$PATH:$ANDROID_HOME/tools

 Step 2 ( .bash_profile / .bashrc ) 
 Reload you .bash_profile Or .bashrc depending on OS

 Step 3 ( go to emulator directory )
 cd /Users/$(whoami)/Library/Android/sdk/emulator

 Step 4 ( Get all list of Advs  )
 emulator -list-avds

 Step 5 ( Run your Emulator Command Mode )
 emulator -avd Nexus_5_API_22_Android_5.1