first re-commit.

pigpio-master/DOC/bin/purge.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+# if backup same as new delete it
+if cmp -s dbase/pigpio.sqlite dbase/pigpio.sqlite.bak
+then
+   rm dbase/pigpio.sqlite.bak
+else
+   d=$(date "+%F-%H-%M-%S")
+   mv -f dbase/pigpio.sqlite.bak dbase/pigpio.sqlite.$d
+fi
+
+# delete backups older than a week
+find dbase/pigpio.sqlite.2* -mtime +7 -delete &>/dev/null
+