nixos/install-grub: don't use bare file handles and 3 argument open

this is not best practice perl since a long time.

<!-- ps-id: 225e1b18-348c-412f-8ecd-394f3ba9a32d -->

Author: Mic92

nixos/modules/system/boot/loader/grub/install-grub.pl

@@ -37,7 +37,8 @@ sub readFile {
     my ($fn) = @_;
     # enable slurp mode: read entire file in one go
     local $/ = undef;
-    open my $fh, "<$fn" or return undef;
+    open my $fh, "<", $fn
+        or return;
     my $s = <$fh>;
     close $fh;
     # disable slurp mode
@@ -48,7 +49,7 @@ sub readFile {
 
 sub writeFile {
     my ($fn, $s) = @_;
-    open my $fh, ">$fn" or die "cannot create $fn: $!\n";
+    open my $fh, ">", $fn or die "cannot create $fn: $!\n";
     print $fh $s or die "cannot write to $fn: $!\n";
     close $fh or die "cannot close $fn: $!\n";
 }
@@ -690,25 +691,25 @@ sub getEfiTarget {
 # because it is read line-by-line.
 sub readGrubState {
     my $defaultGrubState = GrubState->new(name => "", version => "", efi => "", devices => "", efiMountPoint => "", extraGrubInstallArgs => () );
-    open FILE, "<$bootPath/grub/state" or return $defaultGrubState;
+    open my $fh, "<", "$bootPath/grub/state" or return $defaultGrubState;
     local $/ = "\n";
-    my $name = <FILE>;
+    my $name = <$fh>;
     chomp($name);
-    my $version = <FILE>;
+    my $version = <$fh>;
     chomp($version);
-    my $efi = <FILE>;
+    my $efi = <$fh>;
     chomp($efi);
-    my $devices = <FILE>;
+    my $devices = <$fh>;
     chomp($devices);
-    my $efiMountPoint = <FILE>;
+    my $efiMountPoint = <$fh>;
     chomp($efiMountPoint);
     # Historically, arguments in the state file were one per each line, but that
     # gets really messy when newlines are involved, structured arguments
     # like lists are needed (they have to have a separator encoding), or even worse,
     # when we need to remove a setting in the future. Thus, the 6th line is a JSON
     # object that can store structured data, with named keys, and all new state
     # should go in there.
-    my $jsonStateLine = <FILE>;
+    my $jsonStateLine = <$fh>;
     # For historical reasons we do not check the values above for un-definedness
     # (that is, when the state file has too few lines and EOF is reached),
     # because the above come from the first version of this logic and are thus
@@ -720,7 +721,7 @@ sub readGrubState {
     }
     my %jsonState = %{decode_json($jsonStateLine)};
     my @extraGrubInstallArgs = exists($jsonState{'extraGrubInstallArgs'}) ? @{$jsonState{'extraGrubInstallArgs'}} : ();
-    close FILE;
+    close $fh;
     my $grubState = GrubState->new(name => $name, version => $version, efi => $efi, devices => $devices, efiMountPoint => $efiMountPoint, extraGrubInstallArgs => \@extraGrubInstallArgs );
     return $grubState
 }
@@ -787,18 +788,18 @@ sub readGrubState {
     my $stateFile = "$bootPath/grub/state";
     my $stateFileTmp = $stateFile . ".tmp";
 
-    open FILE, ">$stateFileTmp" or die "cannot create $stateFileTmp: $!\n";
-    print FILE get("fullName"), "\n" or die;
-    print FILE get("fullVersion"), "\n" or die;
-    print FILE $efiTarget, "\n" or die;
-    print FILE join( ",", @deviceTargets ), "\n" or die;
-    print FILE $efiSysMountPoint, "\n" or die;
+    open my $fh, ">", "$stateFileTmp" or die "cannot create $stateFileTmp: $!\n";
+    print $fh get("fullName"), "\n" or die;
+    print $fh get("fullVersion"), "\n" or die;
+    print $fh $efiTarget, "\n" or die;
+    print $fh join( ",", @deviceTargets ), "\n" or die;
+    print $fh $efiSysMountPoint, "\n" or die;
     my %jsonState = (
         extraGrubInstallArgs => \@extraGrubInstallArgs
     );
     my $jsonStateLine = encode_json(\%jsonState);
-    print FILE $jsonStateLine, "\n" or die;
-    close FILE or die;
+    print $fh $jsonStateLine, "\n" or die;
+    close $fh or die;
 
     # Atomically switch to the new state file
     rename $stateFileTmp, $stateFile or die "cannot rename $stateFileTmp to $stateFile: $!\n";