diff --git a/action.yml b/action.yml
index e717de5..38d4e13 100644
--- a/action.yml
+++ b/action.yml
@@ -25,6 +25,9 @@ outputs:
     # This compound expression is needed because lhs can be empty.
     # Need to output true and false instead of true and nothing.
     value: ${{ steps.load-cache.outputs.cache-hit || false }}
+  cache-key:
+    description: 'The key where the cache is stored with packages, their versions, and the cache version (i.e. package=version package=version @ 1).'
+    value: ${{ steps.pre-cache.outputs.cache-key }}
   package-version-list:
     description: 'The packages and versions that are installed as a comma delimited list with colon delimit on the package version (i.e. <package>:<version,<package>:<version>).'
     value: ${{ steps.post-cache.outputs.package-version-list }}
@@ -39,6 +42,7 @@ runs:
           "${{ inputs.version }}" \
           ${{ inputs.packages }}
         echo "CACHE_KEY=$(cat ~/cache-apt-pkgs/cache_key.md5)" >> $GITHUB_ENV
+        echo "::set-output name=cache-key::$(cat ~/cache-apt-pkgs/cache_key.md5)"
       shell: bash
 
     - id: load-cache
diff --git a/install_and_cache_pkgs.sh b/install_and_cache_pkgs.sh
index bbf54dc..ca6c838 100755
--- a/install_and_cache_pkgs.sh
+++ b/install_and_cache_pkgs.sh
@@ -4,48 +4,62 @@
 set -e
 
 # Directory that holds the cached packages.
-cache_dir=$1
+cache_dir="${1}"
 
 # List of the packages to use.
 packages="${@:2}"
 
-package_count=$(echo $packages | wc -w)
-echo "Clean installing and caching $package_count package(s)."
+# Sort these packages by name and split on commas.
+packages=$(echo "${packages}" | sed 's/[\s,]+/ /g' | tr ' ' '\n' | sort | tr '\n' ' ')
+
+# Remove extraneous spaces
+packages="$(echo "${packages}" | sed 's/\s\+/ /g;s/^\s\+//g;s/\s\+$//g')"
+
+package_count=$(echo "${packages}" | wc -w)
+echo "Clean installing and caching ${package_count} package(s)."
 echo "Package list:"
-for package in $packages; do
-  echo "- $package"
+for package in ${packages}; do
+  echo "- ${package}"
 done
 
 echo -n "Updating APT package list..."
 sudo apt-get update > /dev/null
 echo "done."
 
-echo "Clean installing and caching $(echo $packages | wc -w) packages..."
-for package in $packages; do
-  cache_filepath=$cache_dir/$package.tar.gz
-
-  echo "- $package"
+manifest=
+echo "Clean installing and caching ${package_count} packages..."
+for package in ${packages}; do
+  echo "- ${package}"
   echo -n "  Installing..."
-  sudo apt-get --yes install $package > /dev/null
+
+  # Gather a list of all packages apt installs to make this package work
+  required_packages=$(apt-get install --dry-run --yes "${package}" | grep -Po "(?<=Inst )[^\s]+" || echo "${package}")
+  echo "Package ${package} installs the following packages: ${required_packages//$'\n'/, }"
+  sudo DEBIAN_FRONTEND=noninteractive apt-get --yes install "${package}" > /dev/null
+
   echo "done."
 
-  echo -n "  Caching to $cache_filepath..."
-  # Pipe all package files (no folders) to Tar.
-  dpkg -L $package |
-    while IFS= read -r f; do     
-      if test -f $f; then echo ${f:1}; fi;  #${f:1} removes the leading slash that Tar disallows
-    done | 
-    xargs tar -czf $cache_filepath -C /    
-  echo "done."
+  for cache_package in ${required_packages}; do
+    cache_filepath="${cache_dir}/${cache_package}.tar.gz"
+    if [ ! -f "${cache_filepath}" ]; then
+      package_name="$(echo "${cache_package}" | cut -d"=" -f1)"
+      echo -n "  Caching ${package_name} to ${cache_filepath}..."
+      # Pipe all package files (no folders) to Tar.
+      dpkg -L "${package_name}" |
+        while IFS= read -r f; do     
+          if test -f $f; then echo "${f:1}"; fi;  #${f:1} removes the leading slash that Tar disallows
+        done | 
+        xargs tar -czf "${cache_filepath}" -C /    
+      echo "done."
+      # Add package to manifest
+      manifest="${manifest}${package_name}:$(dpkg -s "${package_name}" | grep Version | awk '{print $2}'),"
+    fi
+  done
 done
 echo "done."
 
-manifest_filepath="$cache_dir/manifest.log"
-echo -n "Writing package manifest to $manifest_filepath..."
-manifest=
-for package in $packages; do
-  manifest=$manifest$package:$(dpkg -s $package | grep Version | awk '{print $2}'),
-done  
+manifest_filepath="${cache_dir}/manifest.log"
+echo -n "Writing package manifest to ${manifest_filepath}..."
 # Remove trailing comma.
-echo ${manifest:0:-1} > $manifest_filepath
+echo ${manifest:0:-1} > ${manifest_filepath}
 echo "done."
\ No newline at end of file
diff --git a/post_cache_action.sh b/post_cache_action.sh
index 5503013..0bb091f 100755
--- a/post_cache_action.sh
+++ b/post_cache_action.sh
@@ -4,23 +4,23 @@
 set -e
 
 # Directory that holds the cached packages.
-cache_dir=$1
+cache_dir="${1}"
 
 # Root directory to untar the cached packages to.
 # Typically filesystem root '/' but can be changed for testing.
-cache_restore_root=$2
+cache_restore_root="${2}"
 
 # Indicates that the cache was found.
-cache_hit=$3
+cache_hit="${3}"
 
 # List of the packages to use.
 packages="${@:4}"
 
-script_dir=$(dirname $0)
+script_dir="$(dirname -- "$(realpath -- "${0}")")"
 
-if [ "$cache_hit" == true ]; then
-  $script_dir/restore_pkgs.sh ~/cache-apt-pkgs $cache_restore_root
+if [ "${cache_hit}" == true ]; then
+  "${script_dir}/restore_pkgs.sh" ~/cache-apt-pkgs "${cache_restore_root}"
 else
-  $script_dir/install_and_cache_pkgs.sh ~/cache-apt-pkgs $packages
+  "${script_dir}/install_and_cache_pkgs.sh" ~/cache-apt-pkgs "${packages}"
 fi
 echo ""
diff --git a/pre_cache_action.sh b/pre_cache_action.sh
index c4f764b..d9dd664 100755
--- a/pre_cache_action.sh
+++ b/pre_cache_action.sh
@@ -1,40 +1,56 @@
 #!/bin/bash
 
 # Directory that holds the cached packages.
-cache_dir=$1
+cache_dir="${1}"
 
 # Version of the cache to create or load.
-version=$2
+cache_version="${2}"
 
 # List of the packages to use.
-packages=${@:3}
+packages="${@:3}"
+
+# Sort these packages by name and split on commas.
+packages=$(echo "${packages}" | sed 's/[\s,]+/ /g' | tr ' ' '\n' | sort | tr '\n' ' ')
 
 # Create cache directory so artifacts can be saved.
-mkdir -p $cache_dir
+mkdir -p "${cache_dir}"
 
-echo -n "Validating action arguments (version='$version', packages='$packages')...";
-echo $version | grep -o " " > /dev/null
-if [ $? -eq 0 ]; then
+echo -n "Validating action arguments (version='${cache_version}', packages='${packages}')...";
+
+if echo "${cache_version}" | grep -q " " > /dev/null; then
   echo "aborted." 
-  echo "Version value '$version' cannot contain spaces." >&2
+  echo "Version value '${cache_version}' cannot contain spaces." >&2
   exit 1
 fi
-if [ "$packages" == "" ]; then
+if [ "${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."
+
 echo -n "Verifying packages..."
-for package in $packages; do
-  escaped=$(echo $package | sed 's/+/\\+/g')
-  apt-cache search ^$escaped$ | grep $package > /dev/null
-  if [ $? -ne 0 ]; then
+for package in ${packages}; do
+  if echo "${package}" | grep -q "="; then
+    package_name=$(echo "${package}" | cut -d "=" -f1)
+    package_ver=$(echo "${package}" | cut -d "=" -f2)
+  else
+    package_name="${package}"
+  fi
+  apt_show=$(apt show "${package}")
+  if echo ${apt_show} | grep -qi "No packages found" > /dev/null; then
     echo "aborted."
-    echo "Package '$package' not found." >&2
+    echo "Package '${package}' not found." >&2
     exit 3
   fi
+  if [ -z "${package_ver}" ]; then
+    package_ver=$(echo "${apt_show}" | grep -Po "(?<=Version: )[^\s]+")
+  fi
+  package_list="${package_list} ${package_name}=${package_ver}"
 done
 echo "done."
 
@@ -43,18 +59,18 @@ set -e
 
 echo "Creating cache key..."
 
-# Remove package delimiters, sort (requires newline) and then convert back to inline list.
-normalized_list=$(echo $packages | sed 's/[\s,]+/ /g' | tr ' ' '\n' | sort | tr '\n' ' ')
-echo "- Normalized package list is '$normalized_list'."
+# Remove extraneous spaces
+package_list="$(echo "${package_list}" | sed 's/\s\+/ /g;s/^\s\+//g;s/\s\+$//g')"
+echo "- Normalized package list is '$package_list'."
 
-value=$(echo $normalized_list @ $version)
-echo "- Value to hash is '$value'."
+value=$(echo "${package_list} @ ${cache_version}")
+echo "- Value to hash is '${value}'."
 
-key=$(echo $value | md5sum | /bin/cut -f1 -d' ')
+key=$(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 $key_filepath"
+key_filepath="${cache_dir}/cache_key.md5"
+echo "${key}" > "${key_filepath}"
+echo "Hash value written to ${key_filepath}"
diff --git a/restore_pkgs.sh b/restore_pkgs.sh
index ab87879..4fdbcc6 100755
--- a/restore_pkgs.sh
+++ b/restore_pkgs.sh
@@ -4,31 +4,31 @@
 set -e
 
 # Directory that holds the cached packages.
-cache_dir=$1
+cache_dir="${1}"
 
 # Root directory to untar the cached packages to.
 # Typically filesystem root '/' but can be changed for testing.
-cache_restore_root=$2
+cache_restore_root="${2}"
 
-cache_filepaths=$(ls -1 $cache_dir | sort)
-echo "Found $(echo $cache_filepaths | wc -w) files in the cache."
-for cache_filepath in $cache_filepaths; do
-  echo "- $(basename $cache_filepath)"
+cache_filepaths="$(ls -1 "${cache_dir}" | sort)"
+echo "Found $(echo "${cache_filepaths}" | wc -w) files in the cache."
+for cache_filepath in ${cache_filepaths}; do
+  echo "- $(basename "${cache_filepath}")"
 done
 
 echo "Reading from manifest..."
-for logline in $(cat $cache_dir/manifest.log | tr ',' '\n' ); do
-  echo "- $(echo $logline | tr ':' ' ')"
+for logline in $(cat "${cache_dir}/manifest.log" | tr ',' '\n' ); do
+  echo "- $(echo "${logline}" | tr ':' ' ')"
 done
 echo "done."
 
 # Only search for archived results. Manifest and cache key also live here.
-cache_pkg_filepaths=$(ls -1 $cache_dir/*.tar.gz | sort)
-cache_pkg_filecount=$(echo $cache_pkg_filepaths | wc -w)
-echo "Restoring $cache_pkg_filecount packages from cache..."
-for cache_pkg_filepath in $cache_pkg_filepaths; do
-  echo -n "- $(basename $cache_pkg_filepath) restoring..."
-  sudo tar -xf $cache_pkg_filepath -C $cache_restore_root > /dev/null
+cache_pkg_filepaths=$(ls -1 ${cache_dir}/*.tar.gz | sort)
+cache_pkg_filecount=$(echo "${cache_pkg_filepaths}" | wc -w)
+echo "Restoring ${cache_pkg_filecount} packages from cache..."
+for cache_pkg_filepath in ${cache_pkg_filepaths}; do
+  echo -n "- $(basename "${cache_pkg_filepath}") restoring..."
+  sudo tar -xf ${cache_pkg_filepath} -C ${cache_restore_root} > /dev/null
   echo "done."
 done
 echo "done."