buildFHSUserEnvBubblewrap: use arrays for constructing argument list

Generally a cleaner way of doing it and prevents issues with spaces in paths

Used to fix #97234 but #101967 already didt this with a smaller scope

pkgs/build-support/build-fhs-userenv-bubblewrap/default.nix

@@ -50,7 +50,7 @@ let
       "ssl/certs"
       "pki"
     ];
-  in concatStringsSep " \\\n  "
+  in concatStringsSep "\n  "
   (map (file: "--ro-bind-try /etc/${file} /etc/${file}") files);
 
   init = run: writeShellScriptBin "${name}-init" ''
@@ -59,21 +59,21 @@ let
   '';
 
   bwrapCmd = { initArgs ? "" }: ''
-    blacklist="/nix /dev /proc /etc"
-    ro_mounts=""
+    blacklist=(/nix /dev /proc /etc)
+    ro_mounts=()
     for i in ${env}/*; do
       path="/''${i##*/}"
       if [[ $path == '/etc' ]]; then
         continue
       fi
-      ro_mounts="$ro_mounts --ro-bind $i $path"
-      blacklist="$blacklist $path"
+      ro_mounts+=(--ro-bind "$i" "$path")
+      blacklist+=("$path")
     done
 
     if [[ -d ${env}/etc ]]; then
       for i in ${env}/etc/*; do
         path="/''${i##*/}"
-        ro_mounts="$ro_mounts --ro-bind $i /etc$path"
+        ro_mounts+=(--ro-bind "$i" "/etc$path")
       done
     fi
 
@@ -81,24 +81,27 @@ let
     # loop through all directories in the root
     for dir in /*; do
       # if it is a directory and it is not in the blacklist
-      if [[ -d "$dir" ]] && grep -v "$dir" <<< "$blacklist" >/dev/null; then
+      if [[ -d "$dir" ]] && [[ ! "''${blacklist[@]}" =~ "$dir" ]]; then
         # add it to the mount list
         auto_mounts+=(--bind "$dir" "$dir")
       fi
     done
 
-    exec ${bubblewrap}/bin/bwrap \
-      --dev-bind /dev /dev \
-      --proc /proc \
-      --chdir "$(pwd)" \
-      --unshare-all \
-      --share-net \
-      --die-with-parent \
-      --ro-bind /nix /nix \
-      ${etcBindFlags} \
-      $ro_mounts \
-      "''${auto_mounts[@]}" \
+    cmd=(
+      ${bubblewrap}/bin/bwrap
+      --dev-bind /dev /dev
+      --proc /proc
+      --chdir "$(pwd)"
+      --unshare-all
+      --share-net
+      --die-with-parent
+      --ro-bind /nix /nix
+      ${etcBindFlags}
+      "''${ro_mounts[@]}"
+      "''${auto_mounts[@]}"
       ${init runScript}/bin/${name}-init ${initArgs}
+    )
+    exec "''${cmd[@]}"
   '';
 
   bin = writeShellScriptBin name (bwrapCmd { initArgs = ''"$@"''; });