cache-apt-pkgs-action/pre_cache_action.sh

#!/bin/bash

# Include library.
script_dir="$(dirname -- "$(realpath -- "${0}")")"
source "${script_dir}/lib.sh"

# Directory that holds the cached packages.
cache_dir="${1}"

# Version of the cache to create or load.
cache_version="${2}"

# List of the packages to use.
input_packages="${@:3}"

# Trim commas, excess spaces, and sort.
packages="$(normalize_package_list "${input_packages}")"

# Create cache directory so artifacts can be saved.
mkdir -p "${cache_dir}"

echo -n "Validating action arguments (version='${cache_version}', packages='${packages}')...";

if grep -q " " <<< "${cache_version}"; then
  echo "aborted." 
  echo "Version value '${cache_version}' cannot contain spaces." >&2
  exit 1
fi
# Is length of string zero?
if test -z "${packages}"; then
  echo "aborted." 
  echo "Packages argument cannot be empty." >&2
  exit 2
fi
echo "done."

echo -n "Updating APT package list..."
sudo apt-get update > /dev/null
echo "done."

versioned_packages=""
echo -n "Verifying packages..."
for package in ${packages}; do 
  if test ! "$(apt show "${package}")"; then
    echo "aborted."
    echo "Package '${package}' not found." >&2
    exit 3
  fi
  get_package_name_ver "${package}" # -> package_name, package_ver  
  versioned_packages="${versioned_packages} ${package_name}=${package_ver}"
done
echo "done."

# Abort on any failure at this point.
set -e

echo "Creating cache key..."

# TODO Can we prove this will happen again?
normalized_versioned_packages="$(normalize_package_list "${versioned_packages}")"
echo "- Normalized package list is '${normalized_versioned_packages}'."

value="$(echo "${normalized_versioned_packages} @ ${cache_version}")"
echo "- Value to hash is '${value}'."

key="$(echo "${value}" | md5sum | /bin/cut -f1 -d' ')"
echo "- Value hashed as '${key}'."

echo "done."

key_filepath="${cache_dir}/cache_key.md5"
echo "${key}" > "${key_filepath}"
echo "Hash value written to ${key_filepath}"