Porting from Eclipse to Android Studio on mac

First download android studio from here.

Install Android studio from the .dmg file as usual

Now, before opening Android studio, open the terminal and delete the sdk which comes with it.

cd /Applications/Android\ Studio.app
rm -rf sdk

Now create a link of your old sdk in that folder

ln -s [absolute path to old sdk]  /Applications/Android\ Studio.app/sdk

Now open Android studio like any other app and open your existing project. You are good to go!

Or follow this to migrate your eclipse project to gradle!