feat(\db-tool\): introduce unified db-tool package with postgres harness and tests (T0-T8)

legacy/helper/posix-shell/change_namespace.sh

@@ -0,0 +1,41 @@
+: "${OLD_NAMESPACE:=}"
+
+nl=$(printf '\nx')
+nl=${nl%x}
+
+___pop_namespace() {
+    v=${OLD_NAMESPACE%%"$nl"*}
+
+    case $OLD_NAMESPACE in
+        *"$nl"*)
+            OLD_NAMESPACE=${OLD_NAMESPACE#*"$nl"}
+            ;;
+        *)
+            OLD_NAMESPACE=
+            ;;
+    esac
+
+    printf '%s\n' "$v"
+}
+
+___peek_namespace() {
+    printf '%s\n' "${OLD_NAMESPACE%%"$nl"*}"
+}
+
+___push_namespace() {
+    if [ -n "$OLD_NAMESPACE" ]; then
+        OLD_NAMESPACE=$1"$nl$OLD_NAMESPACE"
+    else
+        OLD_NAMESPACE=$1
+    fi
+}
+
+change_namespace() {
+  ___push_namespace "$HECTIC_NAMESPACE"
+  export HECTIC_NAMESPACE="$1"
+}
+
+restore_namespace() {
+  HECTIC_NAMESPACE=$(___pop_namespace)
+  export HECTIC_NAMESPACE
+}