To use with TextBar (http://www.richsomerfield.com/apps/) save to a file and add `osascript /path/to/ShowSpotify.scpt` with an update of about 10 seconds

ShowSpotify.scpt

-- submitted by Luca Zorzi lucazorzi.net

if application "Spotify" is running then
	tell application "Spotify"
		if player state is playing then
			return "♫ " & (artist of current track as string) & " - " & (name of current track as string)
		end if
	end tell
end if

-- EOF

You can also put it all right into TextBar if you want to avoid using a separate file:

osascript -e 'if application "Spotify" is running then' -e 'tell application "Spotify"' -e 'if player state is playing then' -e 'return "♫ " & (artist of current track as string) & " - " & (name of current track as string)' -e 'end if' -e 'end tell' -e 'end if'