printf \\a
and osascript -e beep
play the default alert sound, but they are silent if the alert volume is set to zero. printf \\a
is also silent if an audible bell is disabled.
You could also use afplay or say:
afplay /System/Library/Sounds/Funk.aiff say done
There are more sound effect files in /System/Library/PrivateFrameworks/ScreenReader.framework/Versions/A/Resources/Sounds/.