Use stricter Bash settings in activation script

For example, with these settings Bash will complain if uninitialized
variables are used. Some code has been improved to run cleanly with
these settings.

home-manager/home-manager

@@ -40,7 +40,7 @@ function doBuild() {
         extraArgs="$extraArgs -I $p"
     done
 
-    if [[ $VERBOSE ]]; then
+    if [[ -v VERBOSE ]]; then
         extraArgs="$extraArgs --show-trace"
     fi
 

modules/activation-init.sh

@@ -30,20 +30,20 @@ setupVars
 
 echo "Starting home manager activation"
 
-if [[ $VERBOSE ]]; then
+if [[ -v VERBOSE ]]; then
     export VERBOSE_ECHO=echo
     export VERBOSE_ARG="--verbose"
 else
     export VERBOSE_ECHO=true
-    unset VERBOSE_ARG
+    export VERBOSE_ARG=""
 fi
 
-if [[ $DRY_RUN ]] ; then
+if [[ -v DRY_RUN ]] ; then
     $VERBOSE_ECHO "This is a dry run"
     export DRY_RUN_CMD=echo
 else
     $VERBOSE_ECHO "This is a live run"
-    unset DRY_RUN_CMD
+    export DRY_RUN_CMD=""
 fi
 
 $VERBOSE_ECHO "Activation variables:"

modules/home-environment.nix

@@ -328,7 +328,8 @@ in
         sf = pkgs.writeText "activation-script" ''
           #!${pkgs.stdenv.shell}
 
-          set -e
+          set -eu
+          set -o pipefail
 
           ${builtins.readFile ./activation-init.sh}
 

modules/programs/gnome-terminal.nix

@@ -184,7 +184,7 @@ in
       in
         # The dconf service needs to be installed and prepared.
         stringAfter [ "installPackages" ] ''
-          if [[ $DRY_RUN ]]; then
+          if [[ -v DRY_RUN ]]; then
             echo ${pkgs.gnome3.dconf}/bin/dconf load ${dconfPath} "<" ${sf}
           else
             ${pkgs.gnome3.dconf}/bin/dconf load ${dconfPath} < ${sf}