rewrite scripts

try to provide better syntax and avoid using bash

debian/templates/image.postinst.in

@@ -1,25 +1,27 @@
-#!/bin/sh -e
+#!/bin/sh
+set -e
 
-version=@abiname@@localversion@
-image_path=/boot/@image-stem@-$version
+[ "$1" = configure ] || exit 0
 
-if [ "$1" != configure ]; then
-    exit 0
-fi
+version='@abiname@@localversion@'
+image_path="/boot/@image-stem@-${version}"
 
-depmod $version
+depmod "${version}"
 
-if [ -f /lib/modules/$version/.fresh-install ]; then
+if command -v linux-update-symlinks >/dev/null ; then
     change=install
-else
-    change=upgrade
-fi
-linux-update-symlinks $change $version $image_path
-rm -f /lib/modules/$version/.fresh-install
+    [ -f "/lib/modules/${version}/.fresh-install" ] || change=upgrade
 
-if [ -d /etc/kernel/postinst.d ]; then
-    DEB_MAINT_PARAMS="$*" run-parts --report --exit-on-error --arg=$version \
-	      --arg=$image_path /etc/kernel/postinst.d
+    linux-update-symlinks "${change}" "${version}" "${image_path}"
+fi
+rm -f "/lib/modules/${version}/.fresh-install"
+
+if [ -d /etc/kernel/postinst.d ] ; then
+    DEB_MAINT_PARAMS="$*" \
+    run-parts --report --exit-on-error \
+      "--arg=${version}" \
+      "--arg=${image_path}" \
+    /etc/kernel/postinst.d
 fi
 
 exit 0