How can I open the Atom editor from the command line in OS X?
With the Atom editor open, in the menu bar:
Click Atom → Install Shell Commands
You should expect to see:
Potentially restart your terminal (I did it just out of habit and am not sure if you need to).
When Atom installs, it automatically creates a symbolic link in your /usr/local/bin folder. However, in case it hasn't, you can create it yourself on your Mac:
ln -s /Applications/Atom.app/Contents/Resources/app/atom.sh /usr/local/bin/atom
Now you can use atom folder_name to open a folder and atom file_name to open a file.