diff --git a/demo_source.sh b/demo_source.sh
new file mode 100755
index 0000000..503a48f
--- /dev/null
+++ b/demo_source.sh
@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+## CONSTANTS
+
+## FUNCTIONS
+
+function upgrade {
+  echo UPGRADE
+  sudo -E "$MIAOU_BASH_DIR"/bin/miaou-bash none
+}
+
+function assert_supported_distro {
+  if ! grep -E '^ID=debian|^ID_LIKE=debian' /etc/os-release &&
+    ! grep -E '^ID=arch|^ID_LIKE=arch' /etc/os-release; then
+    local distro
+    distro=$(grep -oP '^ID=\K(.*)' /etc/os-release)
+    >&2 echo "unsupported GNU/Linux distribution: $distro"
+    >&2 echo 'only debian-like OR arch-like currently supported'
+    return 10
+  fi
+}
+
+function assert_bash {
+  if [[ $(basename "$SHELL") != 'bash' ]]; then
+    >&2 echo "MIAOU ERROR: you are running on SHELL=$SHELL rather than 'bash'!"
+    return 11
+  fi
+}
+
+function sudo_root {
+  if [[ "$UID" -ne 0 ]] && ! sudo -vp 'SUDO privilege required: '; then
+    >&2 echo "canceled"
+    return 12
+  fi
+}
+## MAIN
+
+set -Eeuo pipefail
+if assert_supported_distro && assert_bash && sudo_root; then
+  if [[ ! -v MIAOU_BASH_DIR ]]; then
+    MIAOU_BASH_DIR=/opt/miaou-bash
+    export MIAOU_BASH_DIR
+  fi
+  upgrade
+else
+  >&2 echo "MIAOU_BASH_ERROR: requirements failure"
+fi