Add option to preserve build container (RPi-Distro#160)

README.md

@@ -139,6 +139,12 @@ continue:
 CONTINUE=1 ./build-docker.sh
 ```
 
+After successful build, the build container is by default removed. This may be undesired when making incremental changes to a customized build. To prevent the build script from remove the container add
+
+```bash
+PRESERVE_CONTAINER=1 ./build-docker.sh
+```
+
 There is a possibility that even when running from a docker container, the
 installation of `qemu-user-static` will silently fail when building the image
 because `binfmt-support` _must be enabled on the underlying kernel_. An easy

build-docker.sh

@@ -21,6 +21,7 @@ fi
 
 CONTAINER_NAME=${CONTAINER_NAME:-pigen_work}
 CONTINUE=${CONTINUE:-0}
+PRESERVE_CONTAINER=${PRESERVE_CONTAINER:-0}
 
 if [ "$*" != "" ] || [ -z "${IMG_NAME}" ]; then
 	if [ -z "${IMG_NAME}" ]; then
@@ -33,6 +34,7 @@ Usage:
 Optional environment arguments: ( =<default> )
     CONTAINER_NAME=pigen_work  set a name for the build container
     CONTINUE=1                 continue from a previously started container
+    PRESERVE_CONTAINER=1       keep build container even on successful build
 EOF
 	exit 1
 fi
@@ -75,6 +77,10 @@ fi
 echo "copying results from deploy/"
 $DOCKER cp "${CONTAINER_NAME}":/pi-gen/deploy .
 ls -lah deploy
-$DOCKER rm -v $CONTAINER_NAME
+
+# cleanup
+if [ "$PRESERVE_CONTAINER" != "1" ]; then
+	$DOCKER rm -v $CONTAINER_NAME
+fi
 
 echo "Done! Your image(s) should be in deploy/"