badidea.sh

#!/bin/bash
DEVICE="/dev/rdisk0s2"
INITIAL_CHUNK=$((64 * 1024 * 1024))
# Probably want larger on a modern Mac
FINALSIZE=$(( 64 * 1024 )) # 64K is easy enough to eyeball
# Important to split up the target this way
#  so that the script doesn't just find itself!

TARGET="frostbit"
TARGET="${TARGET} moon"

function search_for_text() {
    local input=$1
    local size=$2
    local targetsize=$3
    local target=$4
    local d=""
    if [ -n "${TMPDIR}" ]; then
	d=${TMPDIR}
    else
	d="/tmp"
    fi

    local output="${d}/chunk${size}"

    local tried=0
    local found=0
    while : ; do
	local i=0
	if [ "${tried}" -ne 0 ]; then
	    size=$(( size / 2 ))
	    echo 1>&2 "Missed target in first pass.  Offset ${size}/retry."
	    count=2
	    skip=1
	else
	    skip=0
	    count=1
	fi
	while : ; do
	    echo 1>&2 "Looking for target text in chunk # ${i}"
	    ebs=$(( size * count ))
	    echo 1>&2 "Blocksize ${ebs}"
	    O=$(dd if=${input} of=${output} bs=${size} skip=${skip} count=${count} 2>&1)
	    rc=$?
	    echo 1>&2 "$O"
	    echo "${O}" | grep -q "^0 bytes "
	    rc2=$?
	    if [ ${rc2} -eq 0 ]; then
		echo 1>&2 "No bytes read.  Assuming that means end of disk."
		break
	    fi
	    if [ ${rc} -ne 0 ]; then
		echo 1>&2 "Disk read error."
		break
	    fi
	    grep -q "${target}" ${output}
	    rc=$?
	    if [ ${rc} -eq 0 ]; then
		found=1
		break
	    fi
	    i=$(( i + 1 ))
	    skip=$(( skip + count ))
	done
	if [ ${found} -eq 1 ]; then
	    break
	fi
	if [ ${tried} -eq 1 ]; then
	    break
	fi
	tried=1
    done
    if [ ${found} -ne 1 ] ; then
	# Never found it even after shifting the offset
	echo ""
	return
    fi
    if [ ${size} -le ${targetsize} ]; then
	echo ${output}
	return
    else
	size=$(( size / 64 ))
	if [ ${size} -lt ${targetsize} ]; then
	    size=${targetsize}
	fi
	r=$(search_for_text ${output} ${size} ${targetsize} "${target}")
	echo ${r}
	return
    fi    
}

f=$(search_for_text ${DEVICE} ${INITIAL_CHUNK} ${FINALSIZE} "${TARGET}")
if [ -n "${f}" ]; then
    echo "The text you're looking for is in ${f}."
else
    echo "Sorry, but you're SOL.  The text ain't there."
    exit 2
fi
exit 0