compatibility with alpine shell

build-rpi.sh

@@ -1,29 +1,35 @@
-#!/bin/bash
+#!/bin/sh
 
 # Extracts the rootfs from OpenWRT Raspberry Pi image available from
-# https://downloads.openwrt.org/releases/19.07.2/targets/brcm2708/bcm2708/
+# https://downloads.openwrt.org/releases/19.07.3/targets/brcm2708/bcm2708/
 # and builds a Docker container out of it
 #
 # Refer to https://openwrt.org/toh/raspberry_pi_foundation/raspberry_pi
 # to choose the right image
 #
 # If building on x86, you must have qemu-arm and binfmt-support installed
-set -e
+set -ex
 
-IMG=${1:-'x'}
+IMG=${1:-'image.img'}
 
+check_uid() {
+	if [[ $(id -u) -ne 0 ]]; then
+		echo "this script must be run as root"
+		exit 1
+	fi
+}
 
 mount_rootfs() {
 	echo "* mounting image"
 	offset=$(sfdisk -d ${IMG} | grep "${IMG}2" | sed -E 's/.*start=\s+([0-9]+).*/\1/g')
 	tmpdir=$(mktemp -u -p .)
 	mkdir -p "${tmpdir}"
-	sudo mount -o loop,offset=$((512 * $offset)) -t ext4 ${IMG} ${tmpdir}
+	mount -o loop,offset=$((512 * $offset)) -t ext4 ${IMG} ${tmpdir}
 }
 
 docker_build() {
 	echo "* building Docker image"
-	sudo docker build \
+	docker build \
 		--build-arg ROOT_PW="${ROOT_PW}" \
 		-t ${BUILD_TAG} -f Dockerfile.rpi ${tmpdir}
 }
@@ -31,10 +37,11 @@ docker_build() {
 
 cleanup() {
 	echo "* cleaning up"
-	sudo umount ${tmpdir}
+	umount ${tmpdir} || true
 	rm -rf ${tmpdir}
 }
 
+check_uid
 test -f ${IMG} || { echo 'no image file found'; exit 1; }
 trap cleanup EXIT
 mount_rootfs