diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
new file mode 100644
index 0000000..b44cf5f
--- /dev/null
+++ b/.github/workflows/pull_request.yml
@@ -0,0 +1,29 @@
+name: Pull Request
+on:
+  pull_request:
+    types: [opened, synchronize]
+
+permissions:
+  contents: read
+
+jobs:
+  integrate:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Go
+        uses: actions/setup-go@v4
+        with:
+          go-version-file: "go.mod"
+
+      - name: Build and test
+        run: |
+          go build -v ./...
+          go test -v ./...
+
+      - name: Lint
+        uses: golangci/golangci-lint-action@v3
+        with:
+          version: v1.52.2
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..cf14f3f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+src/cmd/apt_query/apt_query*
\ No newline at end of file
diff --git a/.vscode/launch.json b/.vscode/launch.json
new file mode 100644
index 0000000..cfa9580
--- /dev/null
+++ b/.vscode/launch.json
@@ -0,0 +1,12 @@
+{  
+  "version": "0.2.0",
+  "configurations": [    
+    {
+      "name": "Launch Package",
+      "type": "go",
+      "request": "launch",
+      "mode": "auto",
+      "program": "${fileDirname}",
+    }
+  ]
+}
\ No newline at end of file
diff --git a/README.md b/README.md
index 66a7372..be10067 100644
--- a/README.md
+++ b/README.md
@@ -23,24 +23,24 @@ Create a workflow `.yml` file in your repositories `.github/workflows` directory
 
 There are three kinds of version labels you can use.
 
-* `@latest` - This will give you the latest release.
-* `@v#` - Major only will give you the latest release for that major version only (e.g. `v1`).
-* Branch
-  * `@master` - Most recent manual and automated tested code. Possibly unstable since it is pre-release.
-  * `@staging` - Most recent automated tested code and can sometimes contain experimental features. Is pulled from dev stable code.
-  * `@dev` - Very unstable and contains experimental features. Automated testing may not show breaks since CI is also updated based on code in dev.
+- `@latest` - This will give you the latest release.
+- `@v#` - Major only will give you the latest release for that major version only (e.g. `v1`).
+- Branch
+  - `@master` - Most recent manual and automated tested code. Possibly unstable since it is pre-release.
+  - `@staging` - Most recent automated tested code and can sometimes contain experimental features. Is pulled from dev stable code.
+  - `@dev` - Very unstable and contains experimental features. Automated testing may not show breaks since CI is also updated based on code in dev.
 
 ### Inputs
 
-* `packages` - Space delimited list of packages to install.
-* `version` - Version of cache to load. Each version will have its own cache. Note, all characters except spaces are allowed.
-* `execute_install_scripts` - Execute Debian package pre and post install script upon restore. See [Caveats / Non-file Dependencies](#non-file-dependencies) for more information.
+- `packages` - Space delimited list of packages to install.
+- `version` - Version of cache to load. Each version will have its own cache. Note, all characters except spaces are allowed.
+- `execute_install_scripts` - Execute Debian package pre and post install script upon restore. See [Caveats / Non-file Dependencies](#non-file-dependencies) for more information.
 
 ### Outputs
 
-* `cache-hit` - A boolean value to indicate a cache was found for the packages requested.
-* `package-version-list` - The main requested packages and versions that are installed. Represented as a comma delimited list with equals delimit on the package version (i.e. \<package1>=<version1\>,\<package2>=\<version2>,...).
-* `all-package-version-list` - All the pulled in packages and versions, including dependencies, that are installed. Represented as a comma delimited list with equals delimit on the package version (i.e. \<package1>=<version1\>,\<package2>=\<version2>,...).
+- `cache-hit` - A boolean value to indicate a cache was found for the packages requested.
+- `package-version-list` - The main requested packages and versions that are installed. Represented as a comma delimited list with equals delimit on the package version (i.e. \<package1>=<version1\>,\<package2>=\<version2>,...).
+- `all-package-version-list` - All the pulled in packages and versions, including dependencies, that are installed. Represented as a comma delimited list with equals delimit on the package version (i.e. \<package1>=<version1\>,\<package2>=\<version2>,...).
 
 ### Cache scopes
 
@@ -54,7 +54,6 @@ This was a motivating use case for creating this action.
 name: Create Documentation
 on: push
 jobs:
-  
   build_and_deploy_docs:
     runs-on: ubuntu-latest
     name: Build Doxygen documentation and deploy
@@ -65,7 +64,7 @@ jobs:
           packages: dia doxygen doxygen-doc doxygen-gui doxygen-latex graphviz mscgen
           version: 1.0
 
-      - name: Build        
+      - name: Build
         run: |
           cmake -B ${{github.workspace}}/build -DCMAKE_BUILD_TYPE=${{env.BUILD_TYPE}}      
           cmake --build ${{github.workspace}}/build --config ${{env.BUILD_TYPE}}
@@ -78,15 +77,16 @@ jobs:
 ```
 
 ```yaml
-...
-  install_doxygen_deps:
-    runs-on: ubuntu-latest    
-    steps:
-      - uses: actions/checkout@v2
-      - uses: awalsh128/cache-apt-pkgs-action@latest
-        with:
-          packages: dia doxygen doxygen-doc doxygen-gui doxygen-latex graphviz mscgen
-          version: 1.0
+
+---
+install_doxygen_deps:
+  runs-on: ubuntu-latest
+  steps:
+    - uses: actions/checkout@v2
+    - uses: awalsh128/cache-apt-pkgs-action@latest
+      with:
+        packages: dia doxygen doxygen-doc doxygen-gui doxygen-latex graphviz mscgen
+        version: 1.0
 ```
 
 ## Caveats
@@ -95,8 +95,8 @@ jobs:
 
 This action is based on the principle that most packages can be cached as a fileset. There are situations though where this is not enough.
 
-* Pre and post installation scripts needs to be ran from `/var/lib/dpkg/info/{package name}.[preinst, postinst]`.
-* The Debian package database needs to be queried for scripts above (i.e. `dpkg-query`).
+- Pre and post installation scripts needs to be ran from `/var/lib/dpkg/info/{package name}.[preinst, postinst]`.
+- The Debian package database needs to be queried for scripts above (i.e. `dpkg-query`).
 
 The `execute_install_scripts` argument can be used to attempt to execute the install scripts but they are no guaranteed to resolve the issue.
 
@@ -121,4 +121,4 @@ For more context and information see [issue #57](https://github.com/awalsh128/ca
 
 ### Cache Limits
 
-A repository can have up to 5GB of caches. Once the 5GB limit is reached, older caches will be evicted based on when the cache was last accessed.  Caches that are not accessed within the last week will also be evicted.
+A repository can have up to 5GB of caches. Once the 5GB limit is reached, older caches will be evicted based on when the cache was last accessed. Caches that are not accessed within the last week will also be evicted. To get more information on how to access and manage your actions's caches, see [GitHub Actions / Using workflows / Cache dependencies](https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#viewing-cache-entries).
diff --git a/apt_query b/apt_query
new file mode 100755
index 0000000..db7287f
Binary files /dev/null and b/apt_query differ
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..5cc8b8b
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module awalsh128.com/cache-apt-pkgs-action
+
+go 1.20
diff --git a/lib.sh b/lib.sh
index fd7764d..6531cc2 100755
--- a/lib.sh
+++ b/lib.sh
@@ -99,57 +99,11 @@ function get_normalized_package_list {
   # Remove commas, and block scalar folded backslashes,
   # extraneous spaces at the middle, beginning and end
   # then sort.
-  packages=$(echo "${1}" \
+  local packages=$(echo "${1}" \
     | sed 's/[,\]/ /g; s/\s\+/ /g; s/^\s\+//g; s/\s\+$//g' \
     | sort -t' ')
-
-  # Validate package names and get versions.
-  log_err "resolving package versions..."
-  data=$(apt-cache --quiet=0 --no-all-versions show ${packages} 2>&1 | \
-    grep -E '^(Package|Version|N):')
-  log_err "resolved"
-
-  local ORIG_IFS="${IFS}"
-  IFS=$'\n'
-  declare -A missing
-  local package_versions=''
-  local package='' separator=''
-  for key_value in ${data}; do
-    local key="${key_value%%: *}"
-    local value="${key_value##*: }"
-
-    case $key in
-      Package)
-        package=$value
-        ;;
-      Version)
-        package_versions="${package_versions}${separator}"${package}=${value}""
-        separator=' '
-        ;;
-      N)
-        # Warning messages.
-        case $value in
-          'Unable to locate package '*)
-            package="${value#'Unable to locate package '}"
-            # Avoid duplicate messages.
-            if [ -z "${missing[$package]}" ]; then
-              package="${value#'Unable to locate package '}"
-              log_err "Package '${package}' not found."
-              missing[$package]=1
-            fi
-            ;;
-        esac
-        ;;
-    esac
-  done
-  IFS="${ORIG_IFS}"
-
-  if [ ${#missing[@]} -gt 0 ]; then
-    echo "aborted"
-    exit 5
-  fi
-
-  echo "${package_versions}"
+  local script_dir="$(dirname -- "$(realpath -- "${0}")")"
+  ${script_dir}/apt_query normalized-list ${packages}
 }
 
 ###############################################################################
diff --git a/pre_cache_action.sh b/pre_cache_action.sh
index 23a8fbb..703906c 100755
--- a/pre_cache_action.sh
+++ b/pre_cache_action.sh
@@ -28,7 +28,9 @@ debug="${4}"
 input_packages="${@:5}"
 
 # Trim commas, excess spaces, and sort.
+log "Normalizing package list..."
 packages="$(get_normalized_package_list "${input_packages}")"
+log "done"
 
 # Create cache directory so artifacts can be saved.
 mkdir -p ${cache_dir}
diff --git a/src/cmd/apt_query/main.go b/src/cmd/apt_query/main.go
new file mode 100644
index 0000000..8992a45
--- /dev/null
+++ b/src/cmd/apt_query/main.go
@@ -0,0 +1,109 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+
+	"awalsh128.com/cache-apt-pkgs-action/src/internal/common"
+	"awalsh128.com/cache-apt-pkgs-action/src/internal/exec"
+	"awalsh128.com/cache-apt-pkgs-action/src/internal/logging"
+)
+
+type AptPackage struct {
+	Name    string
+	Version string
+}
+
+type AptPackages []AptPackage
+
+func (ps AptPackages) serialize() string {
+	tokens := []string{}
+	for _, p := range ps {
+		tokens = append(tokens, p.Name+"="+p.Version)
+	}
+	return strings.Join(tokens, " ")
+}
+
+// Gets the APT based packages as a sorted by name list (normalized).
+func getPackages(executor exec.Executor, names []string) AptPackages {
+	prefixArgs := []string{"--quiet=0", "--no-all-versions", "show"}
+	execution := executor.Exec("apt-cache", append(prefixArgs, names...)...)
+
+	err := execution.Error()
+	if err != nil {
+		logging.Fatal(err)
+	}
+
+	pkgs := []AptPackage{}
+	errorMessages := []string{}
+
+	for _, paragraph := range strings.Split(execution.Stdout, "\n\n") {
+		pkg := AptPackage{}
+		for _, line := range strings.Split(paragraph, "\n") {
+			if strings.HasPrefix(line, "Package: ") {
+				pkg.Name = strings.TrimSpace(strings.SplitN(line, ":", 2)[1])
+			} else if strings.HasPrefix(line, "Version: ") {
+				pkg.Version = strings.TrimSpace(strings.SplitN(line, ":", 2)[1])
+			} else if strings.HasPrefix(line, "N: Unable to locate package ") || strings.HasPrefix(line, "E: ") {
+				if !common.ContainsString(errorMessages, line) {
+					errorMessages = append(errorMessages, line)
+				}
+			}
+		}
+		if pkg.Name != "" {
+			pkgs = append(pkgs, pkg)
+		}
+	}
+
+	if len(errorMessages) > 0 {
+		logging.Fatalf("Errors encountered in apt-cache output (see below):\n%s", strings.Join(errorMessages, "\n"))
+	}
+
+	sort.Slice(pkgs, func(i, j int) bool {
+		return pkgs[i].Name < pkgs[j].Name
+	})
+
+	return pkgs
+}
+
+func getExecutor(replayFilename string) exec.Executor {
+	if len(replayFilename) == 0 {
+		return &exec.BinExecutor{}
+	}
+	return exec.NewReplayExecutor(replayFilename)
+}
+
+func main() {
+	debug := flag.Bool("debug", false, "Log diagnostic information to a file alongside the binary.")
+
+	replayFilename := flag.String("replayfile", "",
+		"Replay command output from a specified file rather than executing a binary."+
+			"The file should be in the same format as the log generated by the debug flag.")
+
+	flag.Parse()
+	unparsedFlags := flag.Args()
+
+	logging.Init(os.Args[0]+".log", *debug)
+
+	executor := getExecutor(*replayFilename)
+
+	if len(unparsedFlags) < 2 {
+		logging.Fatalf("Expected at least 2 non-flag arguments but found %d.", len(unparsedFlags))
+		return
+	}
+	command := unparsedFlags[0]
+	pkgNames := unparsedFlags[1:]
+
+	switch command {
+
+	case "normalized-list":
+		pkgs := getPackages(executor, pkgNames)
+		fmt.Println(pkgs.serialize())
+
+	default:
+		logging.Fatalf("Command '%s' not recognized.", command)
+	}
+}
diff --git a/src/cmd/apt_query/main_test.go b/src/cmd/apt_query/main_test.go
new file mode 100644
index 0000000..744e6fd
--- /dev/null
+++ b/src/cmd/apt_query/main_test.go
@@ -0,0 +1,65 @@
+package main
+
+import (
+	"flag"
+	"testing"
+
+	"awalsh128.com/cache-apt-pkgs-action/src/internal/cmdtesting"
+)
+
+var createReplayLogs bool = false
+
+func init() {
+	flag.BoolVar(&createReplayLogs, "createreplaylogs", false, "Execute the test commands, save the command output for future replay and skip the tests themselves.")
+}
+
+func TestMain(m *testing.M) {
+	cmdtesting.TestMain(m)
+}
+
+func TestNormalizedList_MultiplePackagesExists_StdoutsAlphaSortedPackageNameVersionPairs(t *testing.T) {
+	result := cmdtesting.New(t, createReplayLogs).Run("normalized-list", "xdot", "rolldice")
+	result.ExpectSuccessfulOut("rolldice=1.16-1build1 xdot=1.2-3")
+}
+
+func TestNormalizedList_SamePackagesDifferentOrder_StdoutsMatch(t *testing.T) {
+	expected := "rolldice=1.16-1build1 xdot=1.2-3"
+
+	ct := cmdtesting.New(t, createReplayLogs)
+
+	result := ct.Run("normalized-list", "rolldice", "xdot")
+	result.ExpectSuccessfulOut(expected)
+
+	result = ct.Run("normalized-list", "xdot", "rolldice")
+	result.ExpectSuccessfulOut(expected)
+}
+
+func TestNormalizedList_MultiVersionWarning_StdoutSingleVersion(t *testing.T) {
+	var result = cmdtesting.New(t, createReplayLogs).Run("normalized-list", "libosmesa6-dev", "libgl1-mesa-dev")
+	result.ExpectSuccessfulOut("libgl1-mesa-dev=23.0.4-0ubuntu1~23.04.1 libosmesa6-dev=23.0.4-0ubuntu1~23.04.1")
+}
+
+func TestNormalizedList_SinglePackageExists_StdoutsSinglePackageNameVersionPair(t *testing.T) {
+	var result = cmdtesting.New(t, createReplayLogs).Run("normalized-list", "xdot")
+	result.ExpectSuccessfulOut("xdot=1.2-3")
+}
+
+func TestNormalizedList_VersionContainsColon_StdoutsEntireVersion(t *testing.T) {
+	var result = cmdtesting.New(t, createReplayLogs).Run("normalized-list", "default-jre")
+	result.ExpectSuccessfulOut("default-jre=2:1.17-74")
+}
+
+func TestNormalizedList_NonExistentPackageName_StderrsAptCacheErrors(t *testing.T) {
+	var result = cmdtesting.New(t, createReplayLogs).Run("normalized-list", "nonexistentpackagename")
+	result.ExpectError(
+		`Error encountered running apt-cache --quiet=0 --no-all-versions show nonexistentpackagename
+Exited with status code 100; see combined output below:
+N: Unable to locate package nonexistentpackagename
+N: Unable to locate package nonexistentpackagename
+E: No packages found`)
+}
+
+func TestNormalizedList_NoPackagesGiven_StderrsArgMismatch(t *testing.T) {
+	var result = cmdtesting.New(t, createReplayLogs).Run("normalized-list")
+	result.ExpectError("Expected at least 2 non-flag arguments but found 1.")
+}
diff --git a/src/cmd/apt_query/testlogs/testnormalizedlist_multiplepackagesexists_stdoutsalphasortedpackagenameversionpairs.log b/src/cmd/apt_query/testlogs/testnormalizedlist_multiplepackagesexists_stdoutsalphasortedpackagenameversionpairs.log
new file mode 100644
index 0000000..ce1d6c0
--- /dev/null
+++ b/src/cmd/apt_query/testlogs/testnormalizedlist_multiplepackagesexists_stdoutsalphasortedpackagenameversionpairs.log
@@ -0,0 +1,9 @@
+2023/12/10 14:09:15 Debug log created at /home/awalsh128/code/cache-apt-pkgs-action/src/cmd/apt_query/apt_query.log
+2023/12/10 14:09:15 EXECUTION-OBJ-START
+{
+ "Cmd": "apt-cache --quiet=0 --no-all-versions show xdot rolldice",
+ "Stdout": "Package: xdot\nArchitecture: all\nVersion: 1.2-3\nPriority: optional\nSection: universe/python\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Debian Python Team \u003cteam+python@tracker.debian.org\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 160\nDepends: gir1.2-gtk-3.0, graphviz, python3-gi, python3-gi-cairo, python3-numpy, python3:any\nFilename: pool/universe/x/xdot/xdot_1.2-3_all.deb\nSize: 28504\nMD5sum: 9fd56a82e8e6dc2b18fad996dd35bcdb\nSHA1: 9dfa42283c7326da18b132e61369fc8d70534f4b\nSHA256: 0dd59c1840b7f2322cf408f9634c83c4f9766a5e609813147cd67e44755bc011\nSHA512: 33d418475bb9977341007528d8622d236b59a5da4f7fb7f6a36aa05256c4789af30868fc2aad7fc17fb726c8814333cdc579a4ae01597f8f5864b4fbfd8dff14\nHomepage: https://github.com/jrfonseca/xdot.py\nDescription-en: interactive viewer for Graphviz dot files\n xdot is an interactive viewer for graphs written in Graphviz's dot language.\n It uses internally the graphviz's xdot output format as an intermediate\n format, and PyGTK and Cairo for rendering. xdot can be used either as a\n standalone application from command line, or as a library embedded in your\n Python 3 application.\n .\n Features:\n  * Since it doesn't use bitmaps it is fast and has a small memory footprint.\n  * Arbitrary zoom.\n  * Keyboard/mouse navigation.\n  * Supports events on the nodes with URLs.\n  * Animated jumping between nodes.\n  * Highlights node/edge under mouse.\nDescription-md5: eb58f25a628b48a744f1b904af3b9282\n\nPackage: rolldice\nArchitecture: amd64\nVersion: 1.16-1build1\nPriority: optional\nSection: universe/games\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Thomas Ross \u003cthomasross@thomasross.io\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 31\nDepends: libc6 (\u003e= 2.7), libreadline8 (\u003e= 6.0)\nFilename: pool/universe/r/rolldice/rolldice_1.16-1build1_amd64.deb\nSize: 9628\nMD5sum: af6390bf2d5d5b4710d308ac06d4913a\nSHA1: 1d87ccac5b20f4e2a217a0e058408f46cfe5caff\nSHA256: 2e076006200057da0be52060e3cc2f4fc7c51212867173e727590bd7603a0337\nSHA512: a2fa75cfc6f9fc0f1fce3601668bc060f9e10bcf94887025af755ef73db84c55383ed34e4199de53dfbb34377b050c1f9947f29b28d8e527509900f2ec872826\nHomepage: https://github.com/sstrickl/rolldice\nDescription-en: virtual dice roller\n rolldice is a virtual dice roller that takes a string on the command\n line in the format  of some fantasy role playing games like Advanced\n Dungeons \u0026 Dragons [1] and returns the result of the dice rolls.\n .\n [1] Advanced Dungeons \u0026 Dragons is a registered trademark of TSR, Inc.\nDescription-md5: fc24e9e12c794a8f92ab0ca6e1058501\n\n",
+ "Stderr": "",
+ "ExitCode": 0
+}
+EXECUTION-OBJ-END
diff --git a/src/cmd/apt_query/testlogs/testnormalizedlist_multiversionwarning_stdoutsingleversion.log b/src/cmd/apt_query/testlogs/testnormalizedlist_multiversionwarning_stdoutsingleversion.log
new file mode 100644
index 0000000..32b344d
--- /dev/null
+++ b/src/cmd/apt_query/testlogs/testnormalizedlist_multiversionwarning_stdoutsingleversion.log
@@ -0,0 +1,9 @@
+2023/12/10 14:09:17 Debug log created at /home/awalsh128/code/cache-apt-pkgs-action/src/cmd/apt_query/apt_query.log
+2023/12/10 14:09:18 EXECUTION-OBJ-START
+{
+ "Cmd": "apt-cache --quiet=0 --no-all-versions show libosmesa6-dev libgl1-mesa-dev",
+ "Stdout": "Package: libosmesa6-dev\nArchitecture: amd64\nVersion: 23.0.4-0ubuntu1~23.04.1\nMulti-Arch: same\nPriority: extra\nSection: devel\nSource: mesa\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Debian X Strike Force \u003cdebian-x@lists.debian.org\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 51\nProvides: libosmesa-dev\nDepends: libosmesa6 (= 23.0.4-0ubuntu1~23.04.1), mesa-common-dev (= 23.0.4-0ubuntu1~23.04.1) | libgl-dev\nConflicts: libosmesa-dev\nReplaces: libosmesa-dev\nFilename: pool/main/m/mesa/libosmesa6-dev_23.0.4-0ubuntu1~23.04.1_amd64.deb\nSize: 9016\nMD5sum: f2a03da1adaa37afc32493bc52913fe1\nSHA1: 3b0f26ba8438fe6f590cc38d412e0bc1b27f9831\nSHA256: 3fcd3b5c80bde4af1765e588e8f1301ddccae4e052cbfca1a32120d9d8697656\nSHA512: 0a88153218f263511cacffbfe9afd928679f7fa4aacefebd21bafae0517ef1cd3b4bef4fc676e7586728ce1257fbbeb8bd0dda02ddc54fe83c90800f5ce0a660\nHomepage: https://mesa3d.org/\nDescription-en: Mesa Off-screen rendering extension -- development files\n This package provides the required environment for developing programs\n that use the off-screen rendering extension of Mesa.\n .\n For more information on OSmesa see the libosmesa6 package.\nDescription-md5: 9b1d7a0b3e6a2ea021f4443f42dcff4f\n\nPackage: libgl1-mesa-dev\nArchitecture: amd64\nVersion: 23.0.4-0ubuntu1~23.04.1\nMulti-Arch: same\nPriority: extra\nSection: libdevel\nSource: mesa\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Debian X Strike Force \u003cdebian-x@lists.debian.org\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 33\nDepends: libgl-dev, libglvnd-dev\nFilename: pool/main/m/mesa/libgl1-mesa-dev_23.0.4-0ubuntu1~23.04.1_amd64.deb\nSize: 13908\nMD5sum: af15873cbc37ae8719487216f2465a7f\nSHA1: 0a04c22bd32578c65da6cab759347d22cbe2601f\nSHA256: 7b4b377658aff6aaa42af0cf220a64fe7ccd20b53ed0226b6b96edae5ce65dbe\nSHA512: f5b7c9324e7f1f8764a4a035182514559a17a96ce3d43ba570ebd32746de219bea035de3600850134b4f0ba62f12caf0e281fcf7c5490d93e1bd93ca27bfdd22\nHomepage: https://mesa3d.org/\nDescription-en: transitional dummy package\n This is a transitional dummy package, it can be safely removed.\nDescription-md5: 635a93bcd1440d16621693fe064c2aa9\n\n",
+ "Stderr": "N: There are 2 additional records. Please use the '-a' switch to see them.\n",
+ "ExitCode": 0
+}
+EXECUTION-OBJ-END
diff --git a/src/cmd/apt_query/testlogs/testnormalizedlist_nonexistentpackagename_stderrsaptcacheerrors.log b/src/cmd/apt_query/testlogs/testnormalizedlist_nonexistentpackagename_stderrsaptcacheerrors.log
new file mode 100644
index 0000000..7e9e9c2
--- /dev/null
+++ b/src/cmd/apt_query/testlogs/testnormalizedlist_nonexistentpackagename_stderrsaptcacheerrors.log
@@ -0,0 +1,14 @@
+2023/12/10 14:09:19 Debug log created at /home/awalsh128/code/cache-apt-pkgs-action/src/cmd/apt_query/apt_query.log
+2023/12/10 14:09:20 EXECUTION-OBJ-START
+{
+ "Cmd": "apt-cache --quiet=0 --no-all-versions show nonexistentpackagename",
+ "Stdout": "",
+ "Stderr": "N: Unable to locate package nonexistentpackagename\nN: Unable to locate package nonexistentpackagename\nE: No packages found\n",
+ "ExitCode": 100
+}
+EXECUTION-OBJ-END
+2023/12/10 14:09:20 Error encountered running apt-cache --quiet=0 --no-all-versions show nonexistentpackagename
+Exited with status code 100; see combined output below:
+N: Unable to locate package nonexistentpackagename
+N: Unable to locate package nonexistentpackagename
+E: No packages found
diff --git a/src/cmd/apt_query/testlogs/testnormalizedlist_nopackagesgiven_stderrsargmismatch.log b/src/cmd/apt_query/testlogs/testnormalizedlist_nopackagesgiven_stderrsargmismatch.log
new file mode 100644
index 0000000..bd9c530
--- /dev/null
+++ b/src/cmd/apt_query/testlogs/testnormalizedlist_nopackagesgiven_stderrsargmismatch.log
@@ -0,0 +1,2 @@
+2023/12/10 14:09:20 Debug log created at /home/awalsh128/code/cache-apt-pkgs-action/src/cmd/apt_query/apt_query.log
+2023/12/10 14:09:20 Expected at least 2 non-flag arguments but found 1.
diff --git a/src/cmd/apt_query/testlogs/testnormalizedlist_samepackagesdifferentorder_stdoutsmatch.log b/src/cmd/apt_query/testlogs/testnormalizedlist_samepackagesdifferentorder_stdoutsmatch.log
new file mode 100644
index 0000000..c7a9b5b
--- /dev/null
+++ b/src/cmd/apt_query/testlogs/testnormalizedlist_samepackagesdifferentorder_stdoutsmatch.log
@@ -0,0 +1,18 @@
+2023/12/10 14:09:15 Debug log created at /home/awalsh128/code/cache-apt-pkgs-action/src/cmd/apt_query/apt_query.log
+2023/12/10 14:09:16 EXECUTION-OBJ-START
+{
+ "Cmd": "apt-cache --quiet=0 --no-all-versions show rolldice xdot",
+ "Stdout": "Package: rolldice\nArchitecture: amd64\nVersion: 1.16-1build1\nPriority: optional\nSection: universe/games\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Thomas Ross \u003cthomasross@thomasross.io\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 31\nDepends: libc6 (\u003e= 2.7), libreadline8 (\u003e= 6.0)\nFilename: pool/universe/r/rolldice/rolldice_1.16-1build1_amd64.deb\nSize: 9628\nMD5sum: af6390bf2d5d5b4710d308ac06d4913a\nSHA1: 1d87ccac5b20f4e2a217a0e058408f46cfe5caff\nSHA256: 2e076006200057da0be52060e3cc2f4fc7c51212867173e727590bd7603a0337\nSHA512: a2fa75cfc6f9fc0f1fce3601668bc060f9e10bcf94887025af755ef73db84c55383ed34e4199de53dfbb34377b050c1f9947f29b28d8e527509900f2ec872826\nHomepage: https://github.com/sstrickl/rolldice\nDescription-en: virtual dice roller\n rolldice is a virtual dice roller that takes a string on the command\n line in the format  of some fantasy role playing games like Advanced\n Dungeons \u0026 Dragons [1] and returns the result of the dice rolls.\n .\n [1] Advanced Dungeons \u0026 Dragons is a registered trademark of TSR, Inc.\nDescription-md5: fc24e9e12c794a8f92ab0ca6e1058501\n\nPackage: xdot\nArchitecture: all\nVersion: 1.2-3\nPriority: optional\nSection: universe/python\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Debian Python Team \u003cteam+python@tracker.debian.org\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 160\nDepends: gir1.2-gtk-3.0, graphviz, python3-gi, python3-gi-cairo, python3-numpy, python3:any\nFilename: pool/universe/x/xdot/xdot_1.2-3_all.deb\nSize: 28504\nMD5sum: 9fd56a82e8e6dc2b18fad996dd35bcdb\nSHA1: 9dfa42283c7326da18b132e61369fc8d70534f4b\nSHA256: 0dd59c1840b7f2322cf408f9634c83c4f9766a5e609813147cd67e44755bc011\nSHA512: 33d418475bb9977341007528d8622d236b59a5da4f7fb7f6a36aa05256c4789af30868fc2aad7fc17fb726c8814333cdc579a4ae01597f8f5864b4fbfd8dff14\nHomepage: https://github.com/jrfonseca/xdot.py\nDescription-en: interactive viewer for Graphviz dot files\n xdot is an interactive viewer for graphs written in Graphviz's dot language.\n It uses internally the graphviz's xdot output format as an intermediate\n format, and PyGTK and Cairo for rendering. xdot can be used either as a\n standalone application from command line, or as a library embedded in your\n Python 3 application.\n .\n Features:\n  * Since it doesn't use bitmaps it is fast and has a small memory footprint.\n  * Arbitrary zoom.\n  * Keyboard/mouse navigation.\n  * Supports events on the nodes with URLs.\n  * Animated jumping between nodes.\n  * Highlights node/edge under mouse.\nDescription-md5: eb58f25a628b48a744f1b904af3b9282\n\n",
+ "Stderr": "",
+ "ExitCode": 0
+}
+EXECUTION-OBJ-END
+2023/12/10 14:09:16 Debug log created at /home/awalsh128/code/cache-apt-pkgs-action/src/cmd/apt_query/apt_query.log
+2023/12/10 14:09:17 EXECUTION-OBJ-START
+{
+ "Cmd": "apt-cache --quiet=0 --no-all-versions show xdot rolldice",
+ "Stdout": "Package: xdot\nArchitecture: all\nVersion: 1.2-3\nPriority: optional\nSection: universe/python\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Debian Python Team \u003cteam+python@tracker.debian.org\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 160\nDepends: gir1.2-gtk-3.0, graphviz, python3-gi, python3-gi-cairo, python3-numpy, python3:any\nFilename: pool/universe/x/xdot/xdot_1.2-3_all.deb\nSize: 28504\nMD5sum: 9fd56a82e8e6dc2b18fad996dd35bcdb\nSHA1: 9dfa42283c7326da18b132e61369fc8d70534f4b\nSHA256: 0dd59c1840b7f2322cf408f9634c83c4f9766a5e609813147cd67e44755bc011\nSHA512: 33d418475bb9977341007528d8622d236b59a5da4f7fb7f6a36aa05256c4789af30868fc2aad7fc17fb726c8814333cdc579a4ae01597f8f5864b4fbfd8dff14\nHomepage: https://github.com/jrfonseca/xdot.py\nDescription-en: interactive viewer for Graphviz dot files\n xdot is an interactive viewer for graphs written in Graphviz's dot language.\n It uses internally the graphviz's xdot output format as an intermediate\n format, and PyGTK and Cairo for rendering. xdot can be used either as a\n standalone application from command line, or as a library embedded in your\n Python 3 application.\n .\n Features:\n  * Since it doesn't use bitmaps it is fast and has a small memory footprint.\n  * Arbitrary zoom.\n  * Keyboard/mouse navigation.\n  * Supports events on the nodes with URLs.\n  * Animated jumping between nodes.\n  * Highlights node/edge under mouse.\nDescription-md5: eb58f25a628b48a744f1b904af3b9282\n\nPackage: rolldice\nArchitecture: amd64\nVersion: 1.16-1build1\nPriority: optional\nSection: universe/games\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Thomas Ross \u003cthomasross@thomasross.io\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 31\nDepends: libc6 (\u003e= 2.7), libreadline8 (\u003e= 6.0)\nFilename: pool/universe/r/rolldice/rolldice_1.16-1build1_amd64.deb\nSize: 9628\nMD5sum: af6390bf2d5d5b4710d308ac06d4913a\nSHA1: 1d87ccac5b20f4e2a217a0e058408f46cfe5caff\nSHA256: 2e076006200057da0be52060e3cc2f4fc7c51212867173e727590bd7603a0337\nSHA512: a2fa75cfc6f9fc0f1fce3601668bc060f9e10bcf94887025af755ef73db84c55383ed34e4199de53dfbb34377b050c1f9947f29b28d8e527509900f2ec872826\nHomepage: https://github.com/sstrickl/rolldice\nDescription-en: virtual dice roller\n rolldice is a virtual dice roller that takes a string on the command\n line in the format  of some fantasy role playing games like Advanced\n Dungeons \u0026 Dragons [1] and returns the result of the dice rolls.\n .\n [1] Advanced Dungeons \u0026 Dragons is a registered trademark of TSR, Inc.\nDescription-md5: fc24e9e12c794a8f92ab0ca6e1058501\n\n",
+ "Stderr": "",
+ "ExitCode": 0
+}
+EXECUTION-OBJ-END
diff --git a/src/cmd/apt_query/testlogs/testnormalizedlist_singlepackageexists_stdoutssinglepackagenameversionpair.log b/src/cmd/apt_query/testlogs/testnormalizedlist_singlepackageexists_stdoutssinglepackagenameversionpair.log
new file mode 100644
index 0000000..b244b36
--- /dev/null
+++ b/src/cmd/apt_query/testlogs/testnormalizedlist_singlepackageexists_stdoutssinglepackagenameversionpair.log
@@ -0,0 +1,9 @@
+2023/12/10 14:09:18 Debug log created at /home/awalsh128/code/cache-apt-pkgs-action/src/cmd/apt_query/apt_query.log
+2023/12/10 14:09:18 EXECUTION-OBJ-START
+{
+ "Cmd": "apt-cache --quiet=0 --no-all-versions show xdot",
+ "Stdout": "Package: xdot\nArchitecture: all\nVersion: 1.2-3\nPriority: optional\nSection: universe/python\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Debian Python Team \u003cteam+python@tracker.debian.org\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 160\nDepends: gir1.2-gtk-3.0, graphviz, python3-gi, python3-gi-cairo, python3-numpy, python3:any\nFilename: pool/universe/x/xdot/xdot_1.2-3_all.deb\nSize: 28504\nMD5sum: 9fd56a82e8e6dc2b18fad996dd35bcdb\nSHA1: 9dfa42283c7326da18b132e61369fc8d70534f4b\nSHA256: 0dd59c1840b7f2322cf408f9634c83c4f9766a5e609813147cd67e44755bc011\nSHA512: 33d418475bb9977341007528d8622d236b59a5da4f7fb7f6a36aa05256c4789af30868fc2aad7fc17fb726c8814333cdc579a4ae01597f8f5864b4fbfd8dff14\nHomepage: https://github.com/jrfonseca/xdot.py\nDescription-en: interactive viewer for Graphviz dot files\n xdot is an interactive viewer for graphs written in Graphviz's dot language.\n It uses internally the graphviz's xdot output format as an intermediate\n format, and PyGTK and Cairo for rendering. xdot can be used either as a\n standalone application from command line, or as a library embedded in your\n Python 3 application.\n .\n Features:\n  * Since it doesn't use bitmaps it is fast and has a small memory footprint.\n  * Arbitrary zoom.\n  * Keyboard/mouse navigation.\n  * Supports events on the nodes with URLs.\n  * Animated jumping between nodes.\n  * Highlights node/edge under mouse.\nDescription-md5: eb58f25a628b48a744f1b904af3b9282\n\n",
+ "Stderr": "",
+ "ExitCode": 0
+}
+EXECUTION-OBJ-END
diff --git a/src/cmd/apt_query/testlogs/testnormalizedlist_versioncontainscolon_stdoutsentireversion.log b/src/cmd/apt_query/testlogs/testnormalizedlist_versioncontainscolon_stdoutsentireversion.log
new file mode 100644
index 0000000..441de8f
--- /dev/null
+++ b/src/cmd/apt_query/testlogs/testnormalizedlist_versioncontainscolon_stdoutsentireversion.log
@@ -0,0 +1,9 @@
+2023/12/10 14:09:18 Debug log created at /home/awalsh128/code/cache-apt-pkgs-action/src/cmd/apt_query/apt_query.log
+2023/12/10 14:09:19 EXECUTION-OBJ-START
+{
+ "Cmd": "apt-cache --quiet=0 --no-all-versions show default-jre",
+ "Stdout": "Package: default-jre\nArchitecture: amd64\nVersion: 2:1.17-74\nPriority: optional\nSection: interpreters\nSource: java-common (0.74)\nOrigin: Ubuntu\nMaintainer: Ubuntu Developers \u003cubuntu-devel-discuss@lists.ubuntu.com\u003e\nOriginal-Maintainer: Debian Java Maintainers \u003cpkg-java-maintainers@lists.alioth.debian.org\u003e\nBugs: https://bugs.launchpad.net/ubuntu/+filebug\nInstalled-Size: 6\nProvides: java-runtime (= 17), java10-runtime, java11-runtime, java12-runtime, java13-runtime, java14-runtime, java15-runtime, java16-runtime, java17-runtime, java2-runtime, java5-runtime, java6-runtime, java7-runtime, java8-runtime, java9-runtime\nDepends: default-jre-headless (= 2:1.17-74), openjdk-17-jre\nFilename: pool/main/j/java-common/default-jre_1.17-74_amd64.deb\nSize: 912\nMD5sum: e1c24f152396655f96dbaa749bd9cd2e\nSHA1: b1eeca19c6a29448ecc81df249bafdedbe49ee04\nSHA256: 02b1e27de90f05af42d61af927c35f17f7ba1ffe19bf64598ec68216075f623f\nSHA512: 81577c1e4b6920a3fb296a2cdb301131283762efa9fa371e6aa8bc31c7ee1292bbbc442984b2e2ce5d8788507f396eb3e03c1ff8c4dda671f329ac08ec0b2057\nHomepage: https://wiki.debian.org/Java/\nDescription-en: Standard Java or Java compatible Runtime\n This dependency package points to the Java runtime, or Java compatible\n runtime recommended for this architecture, which is\n openjdk-17-jre for amd64.\nDescription-md5: e747dcb24f92ffabcbdfba1db72f26e8\nTask: edubuntu-desktop-gnome\nCnf-Extra-Commands: java,jexec\n\n",
+ "Stderr": "",
+ "ExitCode": 0
+}
+EXECUTION-OBJ-END
diff --git a/src/internal/cmdtesting/cmdtesting.go b/src/internal/cmdtesting/cmdtesting.go
new file mode 100644
index 0000000..30519fd
--- /dev/null
+++ b/src/internal/cmdtesting/cmdtesting.go
@@ -0,0 +1,91 @@
+package cmdtesting
+
+import (
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+
+	"awalsh128.com/cache-apt-pkgs-action/src/internal/common"
+)
+
+const binaryName = "apt_query"
+
+type CmdTesting struct {
+	*testing.T
+	createReplayLogs bool
+	replayFilename   string
+}
+
+func New(t *testing.T, createReplayLogs bool) *CmdTesting {
+	replayFilename := "testlogs/" + strings.ToLower(t.Name()) + ".log"
+	if createReplayLogs {
+		os.Remove(replayFilename)
+		os.Remove(binaryName + ".log")
+	}
+	return &CmdTesting{t, createReplayLogs, replayFilename}
+}
+
+type RunResult struct {
+	Testing     *CmdTesting
+	Combinedout string
+	Err         error
+}
+
+func TestMain(m *testing.M) {
+	cmd := exec.Command("go", "build")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		panic(string(out))
+	}
+	os.Exit(m.Run())
+}
+
+func (t *CmdTesting) Run(command string, pkgNames ...string) RunResult {
+	replayfile := "testlogs/" + strings.ToLower(t.Name()) + ".log"
+
+	flags := []string{"-debug=true"}
+	if !t.createReplayLogs {
+		flags = append(flags, "-replayfile="+replayfile)
+	}
+
+	cmd := exec.Command("./"+binaryName, append(append(flags, command), pkgNames...)...)
+	combinedout, err := cmd.CombinedOutput()
+
+	if t.createReplayLogs {
+		err := common.AppendFile(binaryName+".log", t.replayFilename)
+		if err != nil {
+			t.T.Fatalf("Error encountered appending log file.\n%s", err.Error())
+		}
+	}
+
+	return RunResult{Testing: t, Combinedout: string(combinedout), Err: err}
+}
+
+func (r *RunResult) ExpectSuccessfulOut(expected string) {
+	if r.Testing.createReplayLogs {
+		r.Testing.Log("Skipping test while creating replay logs.")
+		return
+	}
+
+	if r.Err != nil {
+		r.Testing.Errorf("Error running command: %v\n%s", r.Err, r.Combinedout)
+		return
+	}
+	fullExpected := expected + "\n" // Output will always have a end of output newline.
+	if r.Combinedout != fullExpected {
+		r.Testing.Errorf("Unexpected combined std[err,out] found.\nExpected:\n'%s'\nActual:\n'%s'", fullExpected, r.Combinedout)
+	}
+}
+
+func (r *RunResult) ExpectError(expectedCombinedout string) {
+	if r.Testing.createReplayLogs {
+		r.Testing.Log("Skipping test while creating replay logs.")
+		return
+	}
+
+	fullExpectedCombinedout := expectedCombinedout + "\n" // Output will always have a end of output newline.
+	if r.Combinedout != fullExpectedCombinedout {
+		r.Testing.Errorf("Unexpected combined std[err,out] found.\nExpected:\n'%s'\nActual:\n'%s'", fullExpectedCombinedout, r.Combinedout)
+	}
+}
diff --git a/src/internal/common/common.go b/src/internal/common/common.go
new file mode 100644
index 0000000..1191888
--- /dev/null
+++ b/src/internal/common/common.go
@@ -0,0 +1,94 @@
+package common
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+)
+
+func AppendFile(source string, destination string) error {
+	err := createDirectoryIfNotPresent(filepath.Dir(destination))
+	if err != nil {
+		return err
+	}
+	in, err := os.Open(source)
+	if err != nil {
+		return err
+	}
+	defer in.Close()
+
+	out, err := os.OpenFile(destination, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0644)
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+
+	data, err := io.ReadAll(in)
+	if err != nil {
+		return err
+	}
+
+	_, err = out.Write(data)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func CopyFile(source string, destination string) error {
+	err := createDirectoryIfNotPresent(filepath.Dir(destination))
+	if err != nil {
+		return err
+	}
+	in, err := os.Open(source)
+	if err != nil {
+		return err
+	}
+	defer in.Close()
+
+	out, err := os.Create(destination)
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+
+	data, err := io.ReadAll(in)
+	if err != nil {
+		return err
+	}
+
+	_, err = out.Write(data)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func MoveFile(source string, destination string) error {
+	err := createDirectoryIfNotPresent(filepath.Dir(destination))
+	if err != nil {
+		return err
+	}
+	return os.Rename(source, destination)
+}
+
+func ContainsString(arr []string, element string) bool {
+	for _, x := range arr {
+		if x == element {
+			return true
+		}
+	}
+	return false
+}
+
+func createDirectoryIfNotPresent(path string) error {
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		err := os.MkdirAll(path, 0755)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
diff --git a/src/internal/exec/binexecutor.go b/src/internal/exec/binexecutor.go
new file mode 100644
index 0000000..d0a442e
--- /dev/null
+++ b/src/internal/exec/binexecutor.go
@@ -0,0 +1,41 @@
+package exec
+
+import (
+	"bytes"
+	"fmt"
+	"os/exec"
+	"strings"
+
+	"awalsh128.com/cache-apt-pkgs-action/src/internal/logging"
+)
+
+// An executor that proxies command executions from the OS.
+//
+// NOTE: Extra abstraction layer needed for testing and replay.
+type BinExecutor struct{}
+
+func (c *BinExecutor) Exec(name string, arg ...string) *Execution {
+	cmd := exec.Command(name, arg...)
+
+	var stderr bytes.Buffer
+	cmd.Stderr = &stderr
+
+	var stdout bytes.Buffer
+	cmd.Stdout = &stdout
+
+	err := cmd.Run()
+	execution := &Execution{
+		Cmd:      name + " " + strings.Join(arg, " "),
+		Stdout:   stdout.String(),
+		Stderr:   stderr.String(),
+		ExitCode: cmd.ProcessState.ExitCode(),
+	}
+
+	logging.DebugLazy(func() string {
+		return fmt.Sprintf("EXECUTION-OBJ-START\n%s\nEXECUTION-OBJ-END", execution.Serialize())
+	})
+	if err != nil {
+		logging.Fatal(execution.Error())
+	}
+	return execution
+}
diff --git a/src/internal/exec/executor.go b/src/internal/exec/executor.go
new file mode 100644
index 0000000..160dcc7
--- /dev/null
+++ b/src/internal/exec/executor.go
@@ -0,0 +1,50 @@
+package exec
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"awalsh128.com/cache-apt-pkgs-action/src/internal/logging"
+)
+
+type Executor interface {
+	// Executes a command and either returns the output or exits the programs and writes the output (including error) to STDERR.
+	Exec(name string, arg ...string) *Execution
+}
+
+type Execution struct {
+	Cmd      string
+	Stdout   string
+	Stderr   string
+	ExitCode int
+}
+
+// Gets the error, if the command ran with a non-zero exit code.
+func (e *Execution) Error() error {
+	if e.ExitCode == 0 {
+		return nil
+	}
+	return fmt.Errorf(
+		"Error encountered running %s\nExited with status code %d; see combined output below:\n%s",
+		e.Cmd,
+		e.ExitCode,
+		e.Stdout+e.Stderr,
+	)
+}
+
+func DeserializeExecution(payload string) *Execution {
+	var execution Execution
+	err := json.Unmarshal([]byte(payload), &execution)
+	if err != nil {
+		logging.Fatalf("Error encountered deserializing Execution object.\n%s", err)
+	}
+	return &execution
+}
+
+func (e *Execution) Serialize() string {
+	bytes, err := json.MarshalIndent(e, "", " ")
+	if err != nil {
+		logging.Fatalf("Error encountered serializing Execution object.\n%s", err)
+	}
+	return string(bytes)
+}
diff --git a/src/internal/exec/replayexecutor.go b/src/internal/exec/replayexecutor.go
new file mode 100644
index 0000000..674c71d
--- /dev/null
+++ b/src/internal/exec/replayexecutor.go
@@ -0,0 +1,74 @@
+package exec
+
+import (
+	"bufio"
+	"os"
+	"strings"
+
+	"awalsh128.com/cache-apt-pkgs-action/src/internal/logging"
+)
+
+// An executor that replays execution results from a recorded result.
+type ReplayExecutor struct {
+	logFilepath string
+	cmdExecs    map[string]*Execution
+}
+
+func NewReplayExecutor(logFilepath string) *ReplayExecutor {
+	file, err := os.Open(logFilepath)
+	if err != nil {
+		logging.Fatal(err)
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+
+	cmdExecs := make(map[string]*Execution)
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.Contains(line, "EXECUTION-OBJ-START") {
+			payload := ""
+			for scanner.Scan() {
+				line = scanner.Text()
+				if strings.Contains(line, "EXECUTION-OBJ-END") {
+					execution := DeserializeExecution(payload)
+					cmdExecs[execution.Cmd] = execution
+					break
+				} else {
+					payload += line + "\n"
+				}
+			}
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		logging.Fatal(err)
+	}
+	return &ReplayExecutor{logFilepath, cmdExecs}
+}
+
+func (e *ReplayExecutor) getCmds() []string {
+	cmds := []string{}
+	for cmd := range e.cmdExecs {
+		cmds = append(cmds, cmd)
+	}
+	return cmds
+}
+
+func (e *ReplayExecutor) Exec(name string, arg ...string) *Execution {
+	cmd := name + " " + strings.Join(arg, " ")
+	value, ok := e.cmdExecs[cmd]
+	if !ok {
+		var available string
+		if len(e.getCmds()) > 0 {
+			available = "\n" + strings.Join(e.getCmds(), "\n")
+		} else {
+			available = " NONE"
+		}
+		logging.Fatalf(
+			"Unable to replay command '%s'.\n"+
+				"No command found in the debug log; available commands:%s", cmd, available)
+	}
+	return value
+}
diff --git a/src/internal/logging/logger.go b/src/internal/logging/logger.go
new file mode 100644
index 0000000..5b0bcdd
--- /dev/null
+++ b/src/internal/logging/logger.go
@@ -0,0 +1,57 @@
+package logging
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+)
+
+type Logger struct {
+	wrapped  *log.Logger
+	Filename string
+	Debug    bool
+}
+
+var logger *Logger
+
+var LogFilepath = os.Args[0] + ".log"
+
+func Init(filename string, debug bool) *Logger {
+	os.Remove(LogFilepath)
+	file, err := os.OpenFile(LogFilepath, os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		log.Fatal(err)
+		os.Exit(2)
+	}
+	cwd, _ := os.Getwd()
+	logger = &Logger{
+		wrapped:  log.New(file, "", log.LstdFlags),
+		Filename: filepath.Join(cwd, file.Name()),
+		Debug:    debug,
+	}
+	Debug("Debug log created at %s", logger.Filename)
+	return logger
+}
+
+func DebugLazy(getLine func() string) {
+	if logger.Debug {
+		logger.wrapped.Println(getLine())
+	}
+}
+
+func Debug(format string, a ...any) {
+	if logger.Debug {
+		logger.wrapped.Printf(format, a...)
+	}
+}
+
+func Fatal(err error) {
+	fmt.Fprintf(os.Stderr, "%s", err.Error())
+	logger.wrapped.Fatal(err)
+}
+
+func Fatalf(format string, a ...any) {
+	fmt.Fprintf(os.Stderr, format+"\n", a...)
+	logger.wrapped.Fatalf(format, a...)
+}