Apple - Adding a song file to iTunes via the command line without playing the file

You can use the "Automatically Add to iTunes" folder for that (see PH19617):

cp song.mp3 ~/"Music/iTunes/iTunes Media/Automatically Add to iTunes/"

If iTunes is running, anything you copy into this folder will be imported into iTunes automatically (and deleted from the folder afterwards).

Please note:

• The folder name might be language specific, so check the name on your system first.
• Depending on when iTunes was installed, the media folder may be called either iTunes Media or Tunes Music