Resume partial dd transfer

dd-resume.sh

#!/bin/bash -e

# Blocksize to truncate to and buffer by
BS=${BS:-4096}

SELF="`basename $0`"
death() { echo "$SELF:" "$@" >&2; exit 1; }

[ $# -eq 2 ] || death "Usage: $SELF original copy"
SRC="$1"; DST="$2"

# Got SRC?
[ -f "$SRC" ] || death "$SRC: No such file"

# Calculate the number of $BS to skip before we start copying. Default to zero.
SKIP=0; [ ! -f "$DST" ] || SKIP=$(( $(wc --bytes "$DST" | awk '{print $1}' ) / $BS ))

# Do the actual copying.
dd if="$SRC" of="$DST" conv=notrunc bs=$BS skip=$SKIP seek=$SKIP

FYI, there is an issue, as dd is always copying the last (partial) block of the file, because of rounding.
I'm looping over a big list of big files, and have to resume a lot, and that "bug" is not ideal.
Here's how I corrected it :

#!/bin/bash -e

# Blocksize to truncate to and buffer by
BS=${BS:-4096}

SELF="`basename $0`"
death() { echo "$SELF:" "$@" >&2; exit 1; }

[ $# -eq 2 ] || death "Usage: $SELF original copy"
SRC="$1"; DST="$2"

# Got SRC?
[ -f "$SRC" ] || death "$SRC: No such file"

# Compare size of both files
SRCSIZE=$(wc --bytes "$SRC" | awk '{print $1}' )
DSTSIZE=0; [ ! -f "$DST" ] || DSTSIZE=$(wc --bytes "$DST" | awk '{print $1}' )

if [ $SRCSIZE -ne $DSTSIZE ]; then
	# Calculate the number of $BS to skip before we start copying. Default to zero.
	SKIP=0; [ ! -f "$DST" ] || SKIP=$(( $(wc --bytes "$DST" | awk '{print $1}' ) / $BS ))

	[ $SKIP -eq 0 ] || echo "Continuing from $SKIP"

	# Do the actual copying.
	dd if="$SRC" of="$DST" conv=notrunc bs=$BS skip=$SKIP seek=$SKIP status=progress
else
	echo "Files have the same sizes"
fi

Granted I could have reused DSTSIZE in the SKIP calculation, but got lazy.
Note also I added the status=progress to dd to fit my personal preferences.