Initial commit.

new file:   action.yml
	new file:   run.sh

action.yml

@@ -0,0 +1,20 @@
+name: 'Cached APT Install'
+description: 'Install APT based packages and cache them for future runs.'
+inputs:
+  packages:
+    description: 'Space delimited list of packages to install.'
+    required: true
+    default: ''
+runs:
+  using: "composite"
+  steps:
+    - name: Cache Packages
+      uses: actions/cache@v2
+      id: cached-apt-install-packages
+        with:
+          path: "~/cached-apt-install-packages"
+          key: cached-apt-install-packages
+
+    - name: Install Packages
+      run: ${{ github.action_path }}/install.sh "~/cached-apt-install-packages" "${{ inputs.packages }}"
+      shell: bash

run.sh

@@ -0,0 +1,51 @@
+#!/bin/bash -x
+
+cache_dir=$1
+packages="${@:2}"
+
+if [ ! -d "$cache_dir" ]; then
+  echo "Cache directory '$cache_dir' does not exist."
+  exit 1
+fi
+if [ $packages = "" ]; then
+  echo "Packages argument cannot be empty."
+  exit 2
+fi
+
+for dir in `ls $cache_dir`; do
+  remove=true
+  for package in $packages; do
+    if [ $dir == $package ]; then
+      remove=false
+      break
+    fi
+  done
+  [ $remove ] && rm -fr $cache_dir/$dir
+done
+
+for package in $packages; do
+ 
+  package_dir=$cache_dir/$package
+
+  if [ -d $package_dir ]; then
+  
+    echo "Restoring $package from cache $package_dir..."    
+    sudo cp --verbose --force --recursive $package_dir/* /
+    sudo apt-get --yes --only-upgrade install $package
+
+  else
+
+    echo "Clean install $package and caching to $package_dir..."
+    sudo apt-get --yes install $package
+
+    echo "Caching $package to $package_dir..."
+    mkdir --parents $package_dir
+    # Pipe all package files (no folders) to copy command.
+    sudo dpkg -L $package | 
+      while IFS= read -r f; do 
+        if test -f $f; then echo $f; fi;
+      done | 
+      xargs cp -p -t $package_dir
+  fi
+
+done