fix some package hash getting bad input?

README.md

@@ -37,7 +37,7 @@ There are three kinds of version labels you can use.
 - `execute_install_scripts` - Execute Debian package pre and post install script upon restore. See [Caveats / Non-file Dependencies](#non-file-dependencies) for more information.
 - `empty_packages_behavior` - Desired behavior when the given `packages` is empty. `'error'` (default), `'warn'` or `'ignore'`.
 - `add-repository` - Space delimited list of repositories to add via `apt-add-repository` before installing packages. Supports PPA (e.g., `ppa:user/repo`) and other repository formats.
-- `use_aptfile` - Whether to read packages from `Aptfile` at repository root. Set to `false` to disable Aptfile usage even if `Aptfile` exists. Default is `true`.
+- `use_aptfile` - Whether to read packages from `Aptfile` at repository root. Set to `true` to enable Aptfile usage if `Aptfile` exists. Default is `false`.
 
 ### Outputs
 
@@ -124,7 +124,7 @@ install_from_multiple_repos:
 
 ### Using Aptfile
 
-You can also use an `Aptfile` at your repository root to specify packages. The action will automatically read and cache packages from the `Aptfile` if it exists. Comments (lines starting with `#`) and inline comments are supported.
+You can use an `Aptfile` at your repository root to specify packages. To enable Aptfile reading, set `use_aptfile` to `true`. Comments (lines starting with `#`) and inline comments are supported.
 
 **Example Aptfile:**
 ```
@@ -152,6 +152,7 @@ jobs:
       - uses: awalsh128/cache-apt-pkgs-action@latest
         with:
           version: v1
+          use_aptfile: true  # Enable Aptfile reading
           # packages input can be omitted if using Aptfile only
       - name: Build
         run: make
@@ -162,12 +163,13 @@ You can also combine packages from both the input and `Aptfile`:
 - uses: awalsh128/cache-apt-pkgs-action@latest
   with:
     version: v1
+    use_aptfile: true  # Enable Aptfile reading
     packages: protobuf-compiler sd  # Additional packages beyond Aptfile
 ```
 
 ### Disabling Aptfile Usage
 
-If you want to disable Aptfile reading even when an `Aptfile` exists in your repository, set `use_aptfile` to `false`:
+By default, Aptfile reading is disabled (`use_aptfile: false`). If you want to explicitly disable it or ensure it stays disabled, you can set `use_aptfile` to `false`:
 
 ```yaml
 - uses: awalsh128/cache-apt-pkgs-action@latest

action.yml

@@ -42,7 +42,7 @@ inputs:
   use_aptfile:
     description: 'Whether to read packages from Aptfile at repository root. Set to false to disable Aptfile usage even if Aptfile exists.'
     required: false
-    default: 'true'
+    default: 'false'
 
 outputs:
   cache-hit:

lib.sh

@@ -196,8 +196,12 @@ function write_manifest {
     log "Skipped ${1} manifest write. No packages to install."
   else
     log "Writing ${1} packages manifest to ${3}..."
-    # 0:-1 to remove trailing comma, delimit by newline and sort.
-    echo "${2:0:-1}" | tr ',' '\n' | sort > ${3}
+    # Remove trailing comma if present, delimit by newline and sort.
+    local content="${2}"
+    if [ ${#content} -gt 0 ] && [ "${content: -1}" = "," ]; then
+      content="${content:0:-1}"
+    fi
+    echo "${content}" | tr ',' '\n' | sort > "${3}"
     log "done"
   fi
 }

src/internal/common/apt.go

@@ -33,7 +33,10 @@ func isErrLine(line string) bool {
 
 // Resolves virtual packages names to their concrete one.
 func getNonVirtualPackage(executor exec.Executor, name string) (pkg *AptPackage, err error) {
-	execution := executor.Exec("bash", "-c", fmt.Sprintf("apt-cache showpkg %s | grep -A 1 \"Reverse Provides\" | tail -1", name))
+	// Use grep with -A to get the line after "Reverse Provides", then filter out the header line itself
+	// The -v flag filters out lines containing "Reverse Provides" to exclude the header
+	// Then use tail -1 to get the last (first non-header) line, matching original behavior
+	execution := executor.Exec("bash", "-c", fmt.Sprintf("apt-cache showpkg %s | grep -A 1 \"Reverse Provides\" | grep -v \"Reverse Provides\" | tail -1", name))
 	err = execution.Error()
 	if err != nil {
 		logging.Fatal(err)
@@ -42,11 +45,25 @@ func getNonVirtualPackage(executor exec.Executor, name string) (pkg *AptPackage,
 	if isErrLine(execution.CombinedOut) {
 		return pkg, execution.Error()
 	}
-	splitLine := GetSplitLine(execution.CombinedOut, " ", 3)
+	// Trim whitespace and handle the output
+	output := strings.TrimSpace(execution.CombinedOut)
+	if output == "" {
+		return pkg, fmt.Errorf("empty output from apt-cache showpkg for virtual package '%s'", name)
+	}
+	// Skip if the output is the header line "Reverse Provides:" itself (defensive check)
+	if strings.HasPrefix(output, "Reverse Provides") {
+		return pkg, fmt.Errorf("unable to find concrete package for virtual package '%s'. Output was header line: %s", name, output)
+	}
+	splitLine := GetSplitLine(output, " ", 3)
 	if len(splitLine.Words) < 2 {
 		return pkg, fmt.Errorf("unable to parse space delimited line's package name and version from apt-cache showpkg output below:\n%s", execution.CombinedOut)
 	}
-	return &AptPackage{Name: splitLine.Words[0], Version: splitLine.Words[1]}, nil
+	// Validate that we got a valid package name (not "Reverse" or "Provides")
+	packageName := splitLine.Words[0]
+	if packageName == "Reverse" || packageName == "Provides" || strings.HasPrefix(packageName, "Reverse") {
+		return pkg, fmt.Errorf("unable to parse valid package name from apt-cache showpkg output for virtual package '%s'. Output: %s", name, output)
+	}
+	return &AptPackage{Name: packageName, Version: splitLine.Words[1]}, nil
 }
 
 func getPackage(executor exec.Executor, paragraph string) (pkg *AptPackage, err error) {