Fix bug #53046 : sed error starting container on Arch (#433)

run-document-server.sh

@@ -410,6 +410,7 @@ update_welcome_page() {
   WELCOME_PAGE="${APP_DIR}-example/welcome/docker.html"
   if [[ -e $WELCOME_PAGE ]]; then
     DOCKER_CONTAINER_ID=$(basename $(cat /proc/1/cpuset))
+    if (( ${#DOCKER_CONTAINER_ID} >= 12 )); then
       if [[ -x $(command -v docker) ]]; then
         DOCKER_CONTAINER_NAME=$(docker inspect --format="{{.Name}}" $DOCKER_CONTAINER_ID)
         sed 's/$(sudo docker ps -q)/'"${DOCKER_CONTAINER_NAME#/}"'/' -i $WELCOME_PAGE
@@ -417,6 +418,7 @@ update_welcome_page() {
         sed 's/$(sudo docker ps -q)/'"${DOCKER_CONTAINER_ID::12}"'/' -i $WELCOME_PAGE
       fi
     fi
+  fi
 }
 
 update_nginx_settings(){