Docker entrypoint.sh to launch either sh/bash or node depending on the script shebang executable type. This came from a personal circumstance where to save resources, one node image could be used to run shell scripts and node scripts that both performed actions against the same resource. This condensed 4 containers into 1, giving the same result.

entrypoint.sh

#!/bin/sh
set -e

FIRST_LINE=$(head -n 1 "${1}")

# As the scripts can be either JS or shell, determine how to exec!
if [ "${FIRST_LINE}" = "#!/bin/sh" ] || [ "${FIRST_LINE}" = "#!/bin/bash" ]; then
    eval "./$@"
else
    # https://github.com/nodejs/docker-node/blob/master/docker-entrypoint.sh
    if [ "${1#-}" != "${1}" ] || [ -z "$(command -v "${1}")" ]; then
        set -- node "$@"
    fi

    exec "$@"
fi