#!/bin/dash
# USAGE: erase-disk.sh <passes> <device>
# Must be run as root

usage() {
    echo "Usage: erase-disk.sh PASSES DEVICE"
    echo "Securely erase DEVICE with PASSES passes"
    echo
    echo "Flags:"
    echo "  -h, --help \tDisplay this help message"
    echo
    echo "Options:"
    echo "  DEVICE \tThe device to erase"
    echo "  PASSES \tHow many times to erase DEVICE"
    echo
    echo "This script will securely erase a disk device with the specified amount"
    echo "of passes (rounds). It does so by overwriting the specified device with"
    echo "random data on the first pass, and with zeroes on the other passes."
    echo "Due to the nature of disk device access permissions, the script must"
    echo "be run as root."
    echo
    echo "erase-disk.sh is licensed under The Unlicense."

    exit 0
}

[ "$1" = "-h" -o "$1" = "--help" ] && usage

if [ $(id -u) -ne 0 ]; then
    echo "This script must be run as root. Quitting..."
    exit 1
elif [ -z "$1" ]; then
    echo "Please specify number of passes. Quitting..."
    exit 1
elif [ -z "$2" ]; then
    echo "Please specify device to erase. Quitting..."
    exit 1
fi

echo "# Securely erasing the disk device $2"
i=1

while [ $i -le $1 ]; do
    [ $i -eq 1 ] && if="/dev/urandom" || if="/dev/zero"

    echo "\n- Begin pass $i with $if"
    dd if="$if" of="$2" status="progress"
    
    echo "- Syncing I/O"
    sync
    
    i=$(( i + 1 ))
done