docker-letsencrypt-nginx-proxy-companion/app/entrypoint.sh

#!/bin/bash

export CONTAINER_ID=$(cat /proc/self/cgroup | grep 'docker' | sed 's/^.*\///' | tail -n1 | sed 's/^.*-//;s/\..*$//')

if [[ -z "$CONTAINER_ID" ]]; then
    echo "Error: can't get my container ID !" >&2
    exit 1
fi

function check_docker_socket {
	if [[ $DOCKER_HOST == unix://* ]]; then
		socket_file=${DOCKER_HOST#unix://}
		if [[ ! -S $socket_file ]]; then
			cat >&2 <<-EOT
ERROR: you need to share your Docker host socket with a volume at $socket_file
Typically you should run your container with: \`-v /var/run/docker.sock:$socket_file:ro\`
See the documentation at http://git.io/vZaGJ
EOT
			exit 1
		fi
	fi
}
    
function get_nginx_proxy_cid {
	# Look for a NGINX_VERSION environment variable in containers that we have mount volumes from.
    for cid in $(docker inspect --format '{{ range $volume := .HostConfig.VolumesFrom }}{{ $volume }} {{ end}}' $CONTAINER_ID 2>/dev/null); do
		if [[ -n "$(docker exec -t $cid sh -c 'echo -n $NGINX_VERSION')" ]]; then
			export NGINX_PROXY_CID=$cid
			break
		fi
	done
	if [[ -z "$NGINX_PROXY_CID" ]]; then
		echo "Error: can't get nginx-proxy container id !" >&2
		echo "Check that you use the --volumes-from option to mount volumes from the nginx-proxy." >&2
		exit 1
	fi
}

function check_writable_directory {
    local dir="$1"
    if [[ ! -d "$dir" ]]; then
        echo "Error: can't access to '$dir' directory !" >&2
        echo "Check that '$dir' directory is declared has a writable volume." >&2
        exit 1
    fi
    touch $dir/.check_writable 2>/dev/null
    if [[ $? -ne 0 ]]; then
        echo "Error: can't write to the '$dir' directory !" >&2
        echo "Check that '$dir' directory is export as a writable volume." >&2
        exit 1
    fi
    rm -f $dir/.check_writable
}


if [[ "$*" == "/bin/bash /app/start.sh" ]]; then
    check_docker_socket
    get_nginx_proxy_cid
    check_writable_directory '/etc/nginx/certs'
    check_writable_directory '/etc/nginx/vhost.d'
    check_writable_directory '/usr/share/nginx/html'
fi

exec "$@"