Building a patched Ubuntu kernel

build

#!/bin/bash -eu

LINUX_META_PKG='linux-meta'
LINUX_PKG='linux-image-unsigned-"$KERNEL_ABI_VERSION"-generic'

# Enable apt source repositories
sed -i '/^deb /{n; s/^# deb-src/deb-src/;}' /etc/apt/sources.list
apt update
apt install -y dpkg-dev

# Download the linux-meta sources
apt source "$LINUX_META_PKG"
mv "$LINUX_META_PKG"-[0123456789]* linux-meta

# Determine the kernel ABI version referenced by the package 
pushd linux-meta
KERNEL_ABI_VERSION=$(\
    dpkg-parsechangelog -SVersion | awk -F. '{print $1"."$2"."$3"-"$4}')
popd

# Perform environment variable expansion on LINUX_PKG
LINUX_PKG=$(eval "echo ${LINUX_PKG}")

# Download the corresponding unsigned kernel sources
apt source "$LINUX_PKG"
mv "$LINUX_PKG"-[0123456789]* linux

# Install dependencies for these two packages
apt build-dep -y "$LINUX_META_PKG" "$LINUX_PKG"

# Build the packages 
for PKG in linux linux-meta; do
    pushd "$PKG"
    dpkg-buildpackage -rfakeroot -uc -b
    popd
done

For the Raspberry Pi kernel it should be:

LINUX_META_PKG='linux-meta-raspi'
LINUX_PKG='linux-image-"$KERNEL_ABI_VERSION"-raspi'