use process substition + exec instead of pipe (#214)

* improve watchdog so it works on unexpected status.json state

* use process substition + exec instead of pipe

exec in bash doesn't work on pipes
but it works with process subsitition so use that and exec

using exec is generally better due to s6-supervise being able to
properly terminate it

eliminate some permanently running bash using exec sleep

rootfs/etc/s6-overlay/scripts/piaware

@@ -17,4 +17,4 @@ if [ "$VERBOSE_LOGGING" = "true" ]; then
 fi
 
 # shellcheck disable=SC2016
-"${s6wrap[@]}" "${PIAWARE_BIN}" "${PIAWARE_CMD[@]}" | tee -a /var/log/piaware/current
+exec "${s6wrap[@]}" "${PIAWARE_BIN}" "${PIAWARE_CMD[@]}" > >(tee -a /var/log/piaware/current)

rootfs/etc/s6-overlay/scripts/watchdog

@@ -4,13 +4,20 @@
 source /scripts/common
 
 # checking every 60 seconds
-sleep 60
+IVAL=60
+if [[ $(s6-svdt /run/service/watchdog | wc -l) == 0 ]]; then
+    # do nothing on first run
+    exec sleep "$IVAL"
+fi
+
+# set this so the || echo 0 works after the pipe
+set -eo pipefail
 
 # check if the current date is larger than the expiry field of the status json
-if (( $(date +%s) * 1000 > $(grep -o -E -e '(expiry)" *: ([0-9]+)' /run/piaware/status.json | awk '{print $3}') )); then
+if (( $(date +%s) * 1000 > "$(grep -o -E -e '(expiry)" *: ([0-9]+)' /run/piaware/status.json | awk '{print $3}' || echo 0)" )); then
     # current date being larger means piaware is hanging, kill it
     "${s6wrap[@]}" echo "piaware is not updating /run/piaware/status.json, sending SIGKILL"
-    pkill -9 piaware
+    "${s6wrap[@]}" pkill -e -9 piaware
 fi
 
 
@@ -20,3 +27,5 @@ if (( $(wc -l < /var/log/piaware/current) > 800 )); then
     truncate -s 0 /var/log/piaware/current
     cat >> /var/log/piaware/current <<< "$keep"
 fi
+
+exec sleep "$IVAL"