rewrite scripts

try to provide better syntax and avoid using bash

debian/hyperv-daemons.preinst

@@ -1,20 +1,29 @@
 #!/bin/sh
 set -e
 
-if [ "$1" = "upgrade" ]; then
+have_systemd=1
+[ -d /run/systemd/system ] || have_systemd=0
+
+case "$1" in
+upgrade )
     services='kvp vss'
-    if dpkg --compare-versions "$2" lt 6.10~rc6-1~exp1; then
-	services="fcopy $services"
+    if dpkg --compare-versions "$2" lt '6.10~rc6-1~exp1' ; then
+        services="fcopy ${services}"
     fi
-    for i in $services; do
-        if [ -d /run/systemd/system ]; then
-            systemctl stop hyperv-daemons.hv-$i-daemon.service 2>/dev/null || true
+    for i in ${services} ; do
+        init_service="hyperv-daemons.hv-$i-daemon"
+        systemd_unit="${init_service}.service"
+        if [ ${have_systemd} = 1 ] ; then
+            systemctl stop "${systemd_unit}" 2>/dev/null || true
         fi
-        deb-systemd-helper purge hyperv-daemons.hv-$i-daemon.service || true
-        invoke-rc.d --skip-systemd-native hyperv-daemons.hv-$i-daemon stop || true
-        update-rc.d hyperv-daemons.hv-$i-daemon remove || true
-    done
-fi
+        deb-systemd-helper purge "${systemd_unit}" || true
+        invoke-rc.d --skip-systemd-native "${init_service}" stop || true
+        update-rc.d "${init_service}" remove || true
+    done ; unset services i init_service systemd_unit
+;;
+esac
+
+unset have_systemd
 
 #DEBHELPER#