diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
new file mode 100644
index 0000000..e9762fe
--- /dev/null
+++ b/.github/workflows/pull_request.yml
@@ -0,0 +1,21 @@
+name: Pull Request
+on:
+  pull_request:
+    types: [opened, synchronize]
+
+jobs:
+  build_test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: 1.20
+
+      - name: Build and test
+        run: |
+          go build -v
+          go test -v ./...
diff --git a/.vscode/launch.json b/.vscode/launch.json
new file mode 100644
index 0000000..fe7c740
--- /dev/null
+++ b/.vscode/launch.json
@@ -0,0 +1,15 @@
+{
+  // Use IntelliSense to learn about possible attributes.
+  // Hover to view descriptions of existing attributes.
+  // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+  "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/apt_query.go b/apt_query.go
new file mode 100644
index 0000000..91dcfe7
--- /dev/null
+++ b/apt_query.go
@@ -0,0 +1,106 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"sort"
+	"strings"
+)
+
+func contains(arr []string, element string) bool {
+	for _, x := range arr {
+		if x == element {
+			return true
+		}
+	}
+	return false
+}
+
+// Writes a message to STDERR and exits with status 1.
+func exitOnError(format string, arg ...any) {
+	fmt.Fprintln(os.Stderr, fmt.Errorf(format+"\n", arg...))
+	fmt.Println("Usage: apt_query.go normalized-list <package names>")
+	os.Exit(1)
+}
+
+type AptPackage struct {
+	Name    string
+	Version string
+}
+
+// Executes a command and either returns the output or exits the programs and writes the output (including error) to STDERR.
+func execCommand(name string, arg ...string) string {
+	cmd := exec.Command(name, arg...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, fmt.Sprintf("Error code %d encountered while running %s\n%s", cmd.ProcessState.ExitCode(), strings.Join(cmd.Args, " "), string(out)))
+		os.Exit(2)
+	}
+	return string(out)
+}
+
+// Gets the APT based packages as a sorted by name list (normalized).
+func getPackages(names []string) []AptPackage {
+	prefixArgs := []string{"--quiet=0", "--no-all-versions", "show"}
+	out := execCommand("apt-cache", append(prefixArgs, names...)...)
+
+	packages := []AptPackage{}
+	errorMessages := []string{}
+
+	for _, paragraph := range strings.Split(string(out), "\n\n") {
+		pkg := AptPackage{}
+		for _, line := range strings.Split(paragraph, "\n") {
+			if strings.HasPrefix(line, "Package: ") {
+				pkg.Name = strings.TrimSpace(strings.Split(line, ":")[1])
+			} else if strings.HasPrefix(line, "Version: ") {
+				pkg.Version = strings.TrimSpace(strings.Split(line, ":")[1])
+			} else if strings.HasPrefix(line, "N: ") || strings.HasPrefix(line, "E: ") {
+				if !contains(errorMessages, line) {
+					errorMessages = append(errorMessages, line)
+				}
+			}
+		}
+		if pkg.Name != "" {
+			packages = append(packages, pkg)
+		}
+	}
+
+	if len(errorMessages) > 0 {
+		exitOnError("Errors encountered in apt-cache output (see below):\n%s", strings.Join(errorMessages, "\n"))
+	}
+
+	sort.Slice(packages, func(i, j int) bool {
+		return packages[i].Name < packages[j].Name
+	})
+
+	return packages
+}
+
+func serialize(packages []AptPackage) string {
+	tokens := []string{}
+	for _, pkg := range packages {
+		tokens = append(tokens, pkg.Name+"="+pkg.Version)
+	}
+	return strings.Join(tokens, " ")
+}
+
+func main() {
+	const usageText string = "Usage: apt_query.go [normalized-list] <package names>"
+
+	if len(os.Args) < 3 {
+		exitOnError("Expected at least 2 arguments but found %d.", len(os.Args)-1)
+		return
+	}
+
+	command := os.Args[1]
+	packageNames := os.Args[2:]
+
+	switch command {
+	case "normalized-list":
+		fmt.Println(serialize(getPackages(packageNames)))
+		break
+	default:
+		exitOnError("Command '%s' not recognized.", command)
+	}
+}
diff --git a/apt_query_test.go b/apt_query_test.go
new file mode 100644
index 0000000..65beae0
--- /dev/null
+++ b/apt_query_test.go
@@ -0,0 +1,79 @@
+package main
+
+import (
+	"bytes"
+	"os/exec"
+	"testing"
+)
+
+type RunResult struct {
+	TestContext *testing.T
+	Stdout      string
+	Stderr      string
+	Err         error
+}
+
+func run(t *testing.T, command string, pkgNames ...string) RunResult {
+	stdout := &bytes.Buffer{}
+	stderr := &bytes.Buffer{}
+	cmd := exec.Command("go", append([]string{"run", "apt_query.go", command}, pkgNames...)...)
+	cmd.Stdout = stdout
+	cmd.Stderr = stderr
+	err := cmd.Run()
+	return RunResult{TestContext: t, Stdout: stdout.String(), Stderr: stderr.String(), Err: err}
+}
+
+func (r *RunResult) expectSuccessfulOut(expected string) {
+	if r.Err != nil {
+		r.TestContext.Errorf("Error running command: %v", r.Err)
+		return
+	}
+	if r.Stdout != expected+"\n" { // Output will always have a end of output newline.
+		r.TestContext.Errorf("Unexpected stdout found.\nExpected:\n'%s'\nActual:\n'%s'", expected, r.Stdout)
+	}
+}
+
+func (r *RunResult) expectError(expected string) {
+	if r.Stderr != expected+"\n" { // Output will always have a end of output newline.
+		r.TestContext.Errorf("Unexpected stderr found.\nExpected:\n'%s'\nActual:\n'%s'", expected, r.Stderr)
+	}
+}
+
+func TestNormalizedList_MultiplePackagesExists_StdoutsAlphaSortedPackageNameVersionPairs(t *testing.T) {
+	result := run(t, "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"
+
+	result := run(t, "normalized-list", "rolldice", "xdot")
+	result.expectSuccessfulOut(expected)
+
+	result = run(t, "normalized-list", "xdot", "rolldice")
+	result.expectSuccessfulOut(expected)
+}
+
+func TestNormalizedList_SinglePackageExists_StdoutsSinglePackageNameVersionPair(t *testing.T) {
+	var result = run(t, "normalized-list", "xdot")
+	result.expectSuccessfulOut("xdot=1.2-3")
+}
+
+func TestNormalizedList_NonExistentPackageName_StderrsAptCacheErrors(t *testing.T) {
+	var result = run(t, "normalized-list", "nonexistentpackagename")
+	result.expectError(
+		`Error code 100 encountered while running apt-cache --quiet=0 --no-all-versions show nonexistentpackagename
+N: Unable to locate package nonexistentpackagename
+N: Unable to locate package nonexistentpackagename
+E: No packages found
+
+exit status 2`)
+}
+
+func TestNormalizedList_NoPackagesGiven_StderrsArgMismatch(t *testing.T) {
+	var result = run(t, "normalized-list")
+	result.expectError(
+		`Expected at least 2 arguments but found 1.
+
+exit status 1`)
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..96467f4
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module awalsh128.com/cache-apt-pkgs-action
+
+go 1.18