add helper script to extract timestamps from files

path-timestamp.sh

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+# Expose timestamp of given path
+#
+# This will provide the last modification timestamp (technically,
+# stat(1)'s %Y parameter), which is a number of seconds since the
+# epoch, once per provided path. It will claim the timestamp is zero
+# if stat(1) fails to extract the timestamp for any reason.
+#
+# Usage: add this to crontab:
+#
+# */5 * * * * prometheus path-timestamp.sh /var/lib/prometheus | sponge /var/lib/node_exporter/path-timestamp.prom
+#
+# Author: Antoine Beaupré <[email protected]>
+
+echo "# HELP node_path_modification_timestamp_seconds Last change timestamp"
+echo "# TYPE node_path_modification_timestamp_seconds gauge"
+for path in "$@"; do
+    printf 'node_path_modification_timestamp_seconds{path="%s"} ' "$path"
+    stat -c %Y "$path" 2>/dev/null || echo 0
+done