ravenous.dev/tools/tarcat.sh

#!/bin/sh -e
if [ -z "$1" ]; then
	printf 'usage: %s <output> [tar files]...\n' $0 >&2
	echo concatenate tar files >&2
	exit 1
fi

out="$1"

shift 1
while [ -n "$1" ]; do
	if printf %s "$1" | grep -vq '^-'; then # ignore flags
		if ! [ -f "$1" ]; then
			cp "$1" "$out"
		else
			tar --concatenate --file="$out" "$1"
		fi
	fi
	shift 1
done