Use a .new temp file while gathering info, only move it into place on success

src/ssh.go

@@ -209,29 +209,34 @@ func (rb *RouterBackup) BackupCommands(commands []string, outputDir string) erro
 	}
 
 	filename := rb.hostname
-	filepath := filepath.Join(outputDir, filename)
+	finalPath := filepath.Join(outputDir, filename)
+	tempPath := finalPath + ".new"
 
-	// Truncate file at start
-	file, err := os.Create(filepath)
+	// Create temporary file
+	file, err := os.Create(tempPath)
 	if err != nil {
-		return fmt.Errorf("failed to create file %s: %v", filepath, err)
+		return fmt.Errorf("failed to create temporary file %s: %v", tempPath, err)
 	}
 	file.Close()
 
 	successCount := 0
+	hasErrors := false
+
 	for i, command := range commands {
 		fmt.Printf("Running command %d/%d: %s\n", i+1, len(commands), command)
 		output, err := rb.RunCommand(command)
 
 		if err != nil {
 			fmt.Printf("Error executing '%s': %v\n", command, err)
+			hasErrors = true
 			continue
 		}
 
-		// Append to file
-		file, err := os.OpenFile(filepath, os.O_APPEND|os.O_WRONLY, 0644)
+		// Append to temporary file
+		file, err := os.OpenFile(tempPath, os.O_APPEND|os.O_WRONLY, 0644)
 		if err != nil {
 			fmt.Printf("Failed to open file for writing: %v\n", err)
+			hasErrors = true
 			continue
 		}
 
@@ -243,9 +248,21 @@ func (rb *RouterBackup) BackupCommands(commands []string, outputDir string) erro
 	}
 
 	fmt.Printf("Summary: %d/%d commands successful\n", successCount, len(commands))
-	if successCount > 0 {
-		fmt.Printf("Output saved to %s\n", filepath)
+
+	if hasErrors || successCount == 0 {
+		// Remove .new suffix and log error
+		if err := os.Remove(tempPath); err != nil {
+			fmt.Printf("Failed to remove temporary file %s: %v\n", tempPath, err)
+		}
+		return fmt.Errorf("device backup incomplete due to command failures")
 	}
+
+	// All commands succeeded, move file into place atomically
+	if err := os.Rename(tempPath, finalPath); err != nil {
+		return fmt.Errorf("failed to move temporary file to final location: %v", err)
+	}
+
+	fmt.Printf("Output saved to %s\n", finalPath)
 	return nil
 }