Useful for when you want to dual boot with MacOs or not use Grub.

systemd-boot-kernel-updater

#!/usr/bin/env bash
set -eo pipefail;

echo "Fedora Systemd-Boot Kernel Update Script";
echo "================================================================================";

latestVmlinuz="$(ls -t /boot/vmlinuz* | head -1)";
latestVersion="$(echo $latestVmlinuz | sed -e 's~/boot/vmlinuz-~~' -e 's~.x86_64~~')";
echo "Installing latest kernel ($latestVersion) into systemd-boot";

latestVmlinuzHmac="/boot/.vmlinuz-$latestVersion.x86_64.hmac";
latestInitramfs="/boot/initramfs-$latestVersion.x86_64.img";
latestConfig="/boot/config-$latestVersion.x86_64";
latestSystemMap="/boot/System.map-$latestVersion.x86_64";

if [[ ! -f "$latestVmlinuz" || ! -f "$latestVmlinuzHmac" || ! -f "$latestInitramfs" || ! -f "$latestConfig" || ! -f "$latestSystemMap" ]];
then
    echo "Kernel version mis-match, nothing done.";
    exit 1;
fi

echo "Mounting /dev/sda1 /mnt/boot";
if [[ ! -d /mnt/boot ]]; then mkdir -p /mnt/boot; fi
mount /dev/sda1 /mnt/boot;

if [[ -f "/mnt/boot/loader/entries/fedora-$latestVersion.conf" ]];
then
    echo "Kernel is up to date, nothing to do.";
    umount /mnt/boot;
    exit 0;
fi

echo "Copying $latestConfig -> /mnt/boot/fedora/config-$latestVersion.x86_64";
cp $latestConfig /mnt/boot/fedora/;

echo "Copying $latestVmlinuz -> /mnt/boot/fedora/vmlinuz-$latestVersion.x86_64";
cp $latestVmlinuz /mnt/boot/fedora/;

echo "Copying $latestVmlinuzHmac -> /mnt/boot/fedora/.vmlinuz-$latestVersion.x86_64.hmac";
cp $latestVmlinuzHmac /mnt/boot/fedora/;

echo "Copying $latestInitramfs -> /mnt/boot/fedora/initramfs-$latestVersion.x86_64.img";
cp $latestInitramfs /mnt/boot/fedora/;

echo "Copying $latestSystemMap -> /mnt/boot/fedora/System.map-$latestVersion.x86_64";
cp $latestSystemMap /mnt/boot/fedora/;

bootEntry="/mnt/boot/loader/entries/fedora-$latestVersion.conf";
echo "Writing new boot entry ($bootEntry)";
echo -e "title Fedora $latestVersion\n" > $bootEntry;
echo -e "linux /fedora/vmlinuz-$latestVersion.x86_64\n" >> $bootEntry;
echo -e "initrd /fedora/initramfs-$latestVersion.x86_64.img\n" >> $bootEntry;
echo -e "options root=/dev/mapper/fedora-root ro rd.lvm.lv=fedora/root rd.lvm.lv=fedora/swap rhgb quiet LANG=en_AU.UTF-8" >> $bootEntry;

echo "Updating the default entry in (/mnt/boot/loader/loader.conf)";
sed -i "s/^default .*\$/default fedora-$latestVersion/" /mnt/boot/loader/loader.conf

for file in /mnt/boot/fedora/*;
do
    filename="/boot/$(basename $file)";
    if [[ ! -f "$filename" ]];
    then
        echo "Deleting old kernel files $file";
        rm -f "$file";

        if [[ "$filename" == *"/boot/vmlinuz-"* ]];
        then
            oldVersion="$(echo $filename | sed -e 's~/boot/vmlinuz-~~' -e 's~.x86_64~~')";
            echo "Deleting old boot entry /mnt/boot/loader/entries/fedora-$oldVersion.conf";
            rm -f "/mnt/boot/loader/entries/fedora-$oldVersion.conf";
        fi
    fi
done

umount /mnt/boot;