[Docker] Updated bash.sh to use more readable syntax.

Expanding arrays using `"${ARR[@]-}"` instead of
`${ARR[@]+"${ARR[@]}"}`.  This is more vulnerable to typos in the
variable name, but much more readable and much less vulnerable to
typos in the special characters.

Author: Lunderberg

docker/bash.sh

@@ -222,7 +222,7 @@ if [[ -z "${DOCKER_IMAGE_NAME}" ]]; then
     show_usage >&2
 fi
 
-if [[ ${COMMAND[@]+"${COMMAND[@]}"} = bash ]]; then
+if [[ "${COMMAND[@]-}" = bash ]]; then
     INTERACTIVE=true
     USE_NET_HOST=true
 fi
@@ -297,7 +297,7 @@ if ${INTERACTIVE}; then
 fi
 
 # Expose external directories to the docker container
-for MOUNT_DIR in ${MOUNT_DIRS[@]+"${MOUNT_DIRS[@]}"}; do
+for MOUNT_DIR in "${MOUNT_DIRS[@]-}"; do
     DOCKER_MOUNT+=( --volume "${MOUNT_DIR}:${MOUNT_DIR}" )
 done
 
@@ -369,20 +369,20 @@ echo "REPO_DIR: ${REPO_DIR}"
 echo "DOCKER CONTAINER NAME: ${DOCKER_IMAGE_NAME}"
 echo ""
 
-echo Running \'${COMMAND[@]+"${COMMAND[@]}"}\' inside ${DOCKER_IMAGE_NAME}...
+echo "Running '${COMMAND[@]-}' inside ${DOCKER_IMAGE_NAME}..."
 
 DOCKER_CMD=(${DOCKER_BINARY} run
-            ${DOCKER_FLAGS[@]+"${DOCKER_FLAGS[@]}"}
-            ${DOCKER_ENV[@]+"${DOCKER_ENV[@]}"}
-            ${DOCKER_MOUNT[@]+"${DOCKER_MOUNT[@]}"}
-            ${DOCKER_DEVICES[@]+"${DOCKER_DEVICES[@]}"}
+            "${DOCKER_FLAGS[@]-}"
+            "${DOCKER_ENV[@]-}"
+            "${DOCKER_MOUNT[@]-}"
+            "${DOCKER_DEVICES[@]-}"
             "${DOCKER_IMAGE_NAME}"
             bash --login /docker/with_the_same_user
-            ${COMMAND[@]+"${COMMAND[@]}"}
+            "${COMMAND[@]-}"
            )
 
 if ${DRY_RUN}; then
-    echo ${DOCKER_CMD[@]+"${DOCKER_CMD[@]}"}
+    echo "${DOCKER_CMD[@]-}"
 else
-    ${DOCKER_CMD[@]+"${DOCKER_CMD[@]}"}
+    "${DOCKER_CMD[@]-}"
 fi