#!/bin/bash
totalsize=$1
outfile=$2
[[ "$OSTYPE" == "linux-gnu" ]] \
&& filesize=$(stat -c "%s" "$outfile") \
|| filesize=$(stat -f "%z" "$outfile")
padsize=$((512-$filesize))
dd if=/dev/zero bs=1 count=$padsize 2>/dev/null >> "$outfile"