perl script to select which grub.cfg to load from the EFI partition

set-grub-pointer

#!/usr/bin/perl

use Modern::Perl '2018';
use Fatal qw(open);

die "$0 volume-group logical-volume" if @ARGV != 2;

our $vg=$ARGV[0];
our $lv=$ARGV[1];

die "/dev/$vg/$lv doesn't exist" if ! -e "/dev/$vg/$lv";

sub getBlkUUID() {
    my @blk = `blkid |grep $vg-$lv`;
    die "$vg-$lv not unique" if @blk != 1;

    if ($blk[0] =~ /UUID=\"(\S*)\"/) {
	$1;
    } else {
	die "Can't find UUID in $blk[0]"
    }
}

my ($ign, $vgid, $lvid) = split /\s+/, `lvs /dev/$vg/$lv --options vg_uuid,lv_uuid --noheadings`;

open my $fh, ">/boot/efi/EFI/ubuntu/grub.cfg.new";
select $fh;
print "search.fs_uuid ".getBlkUUID()." root lvmid/$vgid/$lvid \n";
print q[set prefix=($root)'/boot/grub'
configfile $prefix/grub.cfg
];