Drupal 9 version always stable

Dockerfile

 FROM ubuntu:20.04
 MAINTAINER Ricardo Amaro <mail_at_ricardoamaro.com>
 ENV DEBIAN_FRONTEND noninteractive
-ARG DRUPALVER=9
+ENV DRUPALVER=9
 
 RUN apt-get update; \
   dpkg-divert --local --rename --add /sbin/initctl; \

files/start.sh

@@ -4,10 +4,10 @@ export BASEHTML="/var/www/html"
 export DOCROOT="/var/www/html/web"
 export GRPID=$(stat -c "%g" /var/lib/mysql/)
 export DRUSH="${DOCROOT}/vendor/bin/drush"
-export LOCAL_IP=$(hostname -I| awk '{print $1}')
+export LOCAL_IP=$(hostname -I | awk '{print $1}')
 export HOSTIP=$(/sbin/ip route | awk '/default/ { print $3 }')
-export DRUPALVER=9.1.x
-echo "${HOSTIP} dockerhost" >> /etc/hosts
+export DRUPALVER=${DRUPALVER:-'9'}
+echo "${HOSTIP} dockerhost" >>/etc/hosts
 echo "Started Container: $(date)"
 
 # Create a basic mysql install
@@ -24,14 +24,17 @@ supervisord -c /etc/supervisor/conf.d/supervisord.conf -l /tmp/supervisord.log
 # If there is no index.php, download drupal
 if [ ! -f ${DOCROOT}/index.php ]; then
   echo "**** No Drupal found. Downloading latest to ${DOCROOT}/ ****"
-  cd ${BASEHTML};
-  # ${DRUSH} -vy dl drupal --default-major=${DRUPALVER} --drupal-project-rename="web"
-  git clone --depth 1 --single-branch -b ${DRUPALVER} \
-      https://git.drupalcode.org/project/drupal.git web;
+  cd ${BASEHTML}
+  # Get the latest version number
+  DV=$(curl -s https://git.drupalcode.org/project/drupal/-/tags?format=atom | grep -e '<title>' | grep -Eo '[0-9\.]+' | sort -nr | grep ^${DRUPALVER} | head -n1)
+  git clone --depth 1 --single-branch -b ${DV} \
+    https://git.drupalcode.org/project/drupal.git web
   # TODO: also require drupal/memcache
-  cd web; composer require drush/drush:~10; composer install
-  chmod a+w ${DOCROOT}/sites/default;
-  mkdir ${DOCROOT}/sites/default/files;
+  cd web
+  composer require drush/drush:~10
+  composer install
+  chmod a+w ${DOCROOT}/sites/default
+  mkdir ${DOCROOT}/sites/default/files
   wget "http://www.adminer.org/latest.php" -O ${DOCROOT}/adminer.php
   chown -R www-data:${GRPID} ${DOCROOT}
   chmod -R ug+w ${DOCROOT}
@@ -40,23 +43,24 @@ else
 fi
 
 # Setup Drupal if services.yml or settings.php is missing
-if ( ! grep -q 'database.*=>.*drupal' ${DOCROOT}/sites/default/settings.php 2>/dev/null); then
+if (! grep -q 'database.*=>.*drupal' ${DOCROOT}/sites/default/settings.php 2>/dev/null); then
   # Generate random passwords
   DRUPAL_DB="drupal"
-  DEBPASS=$(grep password /etc/mysql/debian.cnf |head -n1|awk '{print $3}')
-  ROOT_PASSWORD=`pwgen -c -n -1 12`
-  DRUPAL_PASSWORD=`pwgen -c -n -1 12`
-  echo ${ROOT_PASSWORD} > /var/lib/mysql/mysql/mysql-root-pw.txt
-  echo ${DRUPAL_PASSWORD} > /var/lib/mysql/mysql/drupal-db-pw.txt
+  DEBPASS=$(grep password /etc/mysql/debian.cnf | head -n1 | awk '{print $3}')
+  ROOT_PASSWORD=$(pwgen -c -n -1 12)
+  DRUPAL_PASSWORD=$(pwgen -c -n -1 12)
+  echo ${ROOT_PASSWORD} >/var/lib/mysql/mysql/mysql-root-pw.txt
+  echo ${DRUPAL_PASSWORD} >/var/lib/mysql/mysql/drupal-db-pw.txt
   # Wait for mysql
   echo -n "Waiting for mysql "
   while ! mysqladmin status >/dev/null 2>&1; do
-    echo -n . ; sleep 1;
-  done;
-  echo;
+    echo -n .
+    sleep 1
+  done
+  echo
   # Create and change MySQL creds
   mysqladmin -u root password ${ROOT_PASSWORD} 2>/dev/null
-  echo -e "[client]\npassword=${ROOT_PASSWORD}\n" > /root/.my.cnf
+  echo -e "[client]\npassword=${ROOT_PASSWORD}\n" >/root/.my.cnf
   mysql -e \
     "CREATE USER 'debian-sys-maint'@'localhost' IDENTIFIED WITH mysql_native_password BY '${DEBPASS}';
          GRANT ALL ON *.* TO 'debian-sys-maint'@'localhost';
@@ -85,7 +89,10 @@ chmod -R ug+w ${DOCROOT}/sites/default/
 chown -R mysql:${GRPID} /var/lib/mysql/
 chmod -R ug+w /var/lib/mysql/
 find -type d -exec chmod +xr {} \;
-(sleep 3; drush --root=${DOCROOT}/ cache-rebuild 2>/dev/null) &
+(
+  sleep 3
+  drush --root=${DOCROOT}/ cache-rebuild 2>/dev/null
+) &
 
 echo
 echo "---------------------- USERS CREDENTIALS ($(date +%T)) -------------------------------"