Add clear-caches directive for reducing Docker image sizes

README.md

@@ -36,5 +36,8 @@ hold "ffmpeg"
 
 # Use pins to control package source selection
 pin "*" 600, release: "l=NVIDIA CUDA"
+
+# Clear apt caches to reduce disk usage (useful for Docker images)
+clear-caches
 ```
 

aptfile/main.go

@@ -57,6 +57,9 @@ type HoldDirective struct {
 	PackageName string
 }
 
+type ClearCachesDirective struct {
+}
+
 var (
 	ErrNoDirective = errors.New("no directive found")
 	ErrParsing     = errors.New("error parsing aptfile")
@@ -158,6 +161,8 @@ func ParseLine(lineNum int, line string) (any, error) {
 		return parsePinDirective(cmd, args, opts)
 	case "hold":
 		return parseHoldDirective(cmd, args, opts)
+	case "clear-caches":
+		return parseClearCachesDirective(cmd, args, opts)
 	default:
 		return nil, fmt.Errorf(`unexpected directive "%s"`, cmd)
 	}
@@ -296,3 +301,14 @@ func parseHoldDirective(_ string, args []string, opts map[string]string) (HoldDi
 		PackageName: args[0],
 	}, nil
 }
+
+// clear-caches directive is formatted like, `clear-caches`
+func parseClearCachesDirective(_ string, args []string, opts map[string]string) (ClearCachesDirective, error) {
+	if len(args) > 0 {
+		return ClearCachesDirective{}, fmt.Errorf("expected no arguments, got %v", args)
+	}
+	if len(opts) > 0 {
+		return ClearCachesDirective{}, fmt.Errorf("unexpected options %v", opts)
+	}
+	return ClearCachesDirective{}, nil
+}

aptfile/main_test.go

@@ -84,6 +84,11 @@ func TestParseLine(t *testing.T) {
 			line:     "hold curl",
 			expected: HoldDirective{PackageName: "curl"},
 		},
+		{
+			name:     "clear-caches directive",
+			line:     "clear-caches",
+			expected: ClearCachesDirective{},
+		},
 		{
 			name:    "invalid syntax",
 			line:    "package foo: bar",

main.go

@@ -84,6 +84,7 @@ func processAptfile(path string, dryRun bool) {
 	}
 
 	pkgs := make([]aptfile.PackageDirective, 0)
+	clearCachesDirectives := make([]aptfile.ClearCachesDirective, 0)
 
 	// First pass, skip package installation (except for .deb files,
 	// which can be necessary for setting up repos or keyrings, etc.)
@@ -117,6 +118,9 @@ func processAptfile(path string, dryRun bool) {
 			if err := addHold(dir, dryRun); err != nil {
 				log.Fatalf("Failed to add hold: %v", err)
 			}
+		case aptfile.ClearCachesDirective:
+			// Defer clear-caches to run after packages are installed
+			clearCachesDirectives = append(clearCachesDirectives, dir)
 		default:
 			log.Fatalf("Unknown directive: %v", d)
 		}
@@ -126,6 +130,13 @@ func processAptfile(path string, dryRun bool) {
 	if err != nil {
 		log.Fatalf("Failed to install packages: %v", err)
 	}
+
+	// Execute clear-caches once if any directives exist
+	if len(clearCachesDirectives) > 0 {
+		if err := clearCaches(dryRun); err != nil {
+			log.Fatalf("Failed to clear caches: %v", err)
+		}
+	}
 }
 
 func installPackages(pkgs []aptfile.PackageDirective, dryRun bool) error {
@@ -401,3 +412,35 @@ func addHold(hold aptfile.HoldDirective, dryRun bool) error {
 		return fixCmd.Run()
 	}
 }
+
+func clearCaches(dryRun bool) error {
+	if dryRun {
+		fmt.Println("[dry-run] Would run `apt-get clean`")
+		fmt.Println("[dry-run] Would remove /var/lib/apt/lists/*")
+		return nil
+	}
+
+	fmt.Println("Clearing apt caches...")
+
+	// Run apt-get clean to clear package cache
+	cleanCmd := exec.Command("apt-get", "clean")
+	cleanCmd.Env = append(os.Environ(), "DEBIAN_FRONTEND=noninteractive")
+	cleanCmd.Stdout = os.Stdout
+	cleanCmd.Stderr = os.Stderr
+	if err := cleanCmd.Run(); err != nil {
+		return fmt.Errorf("error running apt-get clean: %w", err)
+	}
+
+	// Remove apt lists to reduce size further
+	// Use sh -c to ensure glob expansion works
+	fmt.Println("Removing apt package lists...")
+	rmCmd := exec.Command("sh", "-c", "rm -rf /var/lib/apt/lists/*")
+	rmCmd.Stdout = os.Stdout
+	rmCmd.Stderr = os.Stderr
+	if err := rmCmd.Run(); err != nil {
+		return fmt.Errorf("error removing apt lists: %w", err)
+	}
+
+	fmt.Println("Cache clearing completed")
+	return nil
+}