Alarm clock in bash

alarm.sh

#!/bin/bash

# add to sudoers
# username ALL = (root) NOPASSWD: /usr/sbin/rtcwake

DATE="$@"
SONG="$HOME/.usr/share/alarm.mp3"

if ! command -v mplayer &>/dev/null
then
    echo "Can't play alarm. MPlayer needs to be installed."
    exit 1
fi

if ! command -v rtcwake &>/dev/null
then
    echo "Can't suspend machine. RTCwake needs to be installed."
    exit 1
fi

if ! date -d "$DATE" >/dev/null 2>&1
then
    echo "Invalid date: $DATE"
    echo "Usage: $0 tomorrow 8:00"
    exit 1
fi

CURRENT_EPOCH=$(date +%s)
TARGET_EPOCH=$(date -d "$DATE" +%s)

if (( $CURRENT_EPOCH > $TARGET_EPOCH ))
then
    echo "Past date: $DATE"
    exit 1
fi

dbus-send --type=method_call --dest=org.gnome.ScreenSaver /org/gnome/ScreenSaver org.gnome.ScreenSaver.Lock

sudo rtcwake -m mem -t $TARGET_EPOCH

CURRENT_EPOCH=$(date +%s)
while (( $CURRENT_EPOCH < $TARGET_EPOCH ))
do
    SECONDS=$(( $TARGET_EPOCH - $CURRENT_EPOCH ))
    if (( $SECONDS > 5 ))
    then
        SECONDS=5
    fi

    sleep $SECONDS
    CURRENT_EPOCH=$(date +%s)
done

echo "Press ctrl+C to end alarm"
mplayer -loop 0 "$SONG" &>/dev/null