Hash per block for large files

hashblock.sh

#!/usr/bin/env bash

set -o nounset
set -o noclobber

export LC_ALL=C
export PATH="/bin:/sbin:/usr/bin:/usr/sbin:$PATH"

readonly MYSELF="$(readlink -f $0)"
readonly MYPATH="${MYSELF%/*}"

# Defualt to 1G Block + MD5
typeset -i BLOCKSIZE="$((1024*1024*1024))"
typeset    HASHFUNC="md5sum"
typeset -i STARTSIZE=0
typeset -i STOPSIZE=0

# Copy stdin for output
exec 3>&1
function hashstdin {
	# Consume stdin
	typeset h="$($HASHFUNC -)"
	echo >&3 "$@: $h"
}


# Very basic option parsing
while [[ -n "${1:-}" ]]; do
	# Stop if option does not start with --
	[[ "${1#--}" == "${1}" ]] && break

	case "$1" in
		--blocksize)    BLOCKSIZE="${2:-}"; shift ;;
		--blocksize=*)  BLOCKSIZE="${1#*=}"       ;;
		--hash)         HASHFUNC="${2}"; shift    ;;
		--hash=*)       HASHFUNC="${1#*=}"        ;;
		--startsize)    STARTSIZE="${2}"; shift   ;;
		--startsize=*)  STARTSIZE="${1#*=}";      ;;
		--stopsize)     STOPSIZE="${2}"; shift    ;;
		--stopsize=*)   STOPSIZE="${1#*=}";       ;;
		*) echo >&2 "Error: Unknown option: $1"; exit 1 ;;
	esac
	shift
done

#
# Check user values
#

if [[ -z "$HASHFUNC" ]] || ! type -p $HASHFUNC >/dev/null; then
	echo >&2 "Error: Unknown hash function: $HASHFUNC"
	exit 1
fi


typeset FILE="${1:-}"
if ! [[ -s "$FILE" ]]; then
	echo >&2 "Error: non-existant or empty file '$FILE'"
	exit 1
fi


#
# Calculated values
#

typeset -i FILESIZE="$(stat -c %s "$FILE")"
typeset -i gb="$(( 1024 * 1024 * 1024 ))"

# Defaults to 10 chunks
if [[ $BLOCKSIZE == 0 ]]; then
	# Less than 10G, use 1G chunks
	if [[ $FILESIZE -lt $(( 10 *$gb)) ]]; then
		BLOCKSIZE="$(( 1*$gb ))"
		[[ $BLOCKSIZE -gt $FILESIZE ]] && BLOCKSIZE=$FILESIZE
	# More than 10G, do 10 blocks
	else
		BLOCKSIZE=$(( $FILESIZE / 10 ))
	fi
fi

typeset BLOCKCNT="$(($FILESIZE / $BLOCKSIZE))"
typeset -i blocknum=0

[[ $STARTSIZE -ne 0 ]] && blocknum="$(( $STARTSIZE / $BLOCKSIZE ))"
[[ $STOPSIZE  -ne 0 ]] && BLOCKCNT="$(( $STOPSIZE / $BLOCKSIZE ))"



while [[ $blocknum -le $BLOCKCNT ]]; do
	typeset -i skip="$blocknum"
	dd if="$FILE" bs=$BLOCKSIZE count=1 skip=$skip 2>/dev/null | tee >(hashstdin "Block $blocknum ($(( $BLOCKSIZE*$skip )) - $(($BLOCKSIZE*($skip + 1) )))")
	blocknum+=1
done | hashstdin "Whole file: ($FILESIZE)"