How to eject all drives from the command-line
You can use the in-built AppleScript solution, as mentioned in this thread and this page, by adding this to ~/.bash_profile:

alias ejectall='osascript -e "tell application \"Finder\" to eject (every disk whose ejectable is true)"'


This will require you giving permission to Terminal to control Finder, or you will get this error:

execution error: Not authorised to send Apple events to Finder. (-1743)


If you want a pure bash solution, here is a function that you can call with ejectall. If you renamed your startup disk or have different Time Machine backups, you may need to edit the condition that filters out the drives.

ejectall() {
    total=0
    ejected=0

    for v in /Volumes/*; do
    if [[ $v != *"Macintosh HD" &amp;&amp; $v != *"com.apple.TimeMachine"* ]]; then
        echo "Ejecting $v..."
        diskutil eject "$v"

        if [ $? -eq 0 ]; then
        ejected=$(($ejected + 1))
        fi
        total=$(($total + 1))
    fi
    done

    if [ $total -eq 0 ]; then
    echo "No drives to eject"
    else
    msg="$ejected drive(s) ejected"
    failed=$(($total - $ejected))
    if [ $failed -gt 0 ]; then
        msg="$msg, $failed drive(s) failed to eject"
    fi
    echo $msg
    fi
}


Both methods will also work for CDs.