+# we want to run if any of the following things is true
+# - we have never run before
+# - var/lib/dpkg/status has been touched since the last run
+# - var/cache/apt/pkgcache.bin has been touched since the last run
+# - our last run ended with 'apt-get update failed'
+# - our last run has been more than MAX_AGE (23hrs) ago
+run_required() {
+ local run=0
+ local norun=1
+
+ [ -e "$STATUS" ] || return $run
+ [ /var/lib/dpkg/status -nt "$STATUS" ] && return $run
+ [ /var/cache/apt/pkgcache.bin -nt "$STATUS" ] && return $run
+ grep "apt-get update failed" "$STATUS" > /dev/null && return $run
+
+ local last_mod
+ last_mod=`stat -c "%Y" "$STATUS"`
+ now=`date +%s`
+ age=$(( $now - $last_mod ))
+ [ "$age" -gt "$MAX_AGE" ] && return $run
+
+ return $norun
+}
+
+# do stuff only when required
+run_required || exit
+
+# sleep if called non-interactively