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How to Write a Value to the Registry in a Batch Script

Writing to the Windows Registry is a powerful administrative capability that allows a script to change system configurations, set application preferences, or store its own persistent settings. The standard, built-in command-line tool for all registry operations is the versatile REG.EXE.

This guide will teach you how to use the REG ADD command to create new registry values or modify existing ones. You will learn the syntax for different data types (like strings and numbers), the critical importance of running with the correct permissions, and the essential switches needed to make your script run silently and without user interaction.

CRITICAL WARNING: Editing the registry is a high-risk operation. An incorrect change, a typo in a key path, or a wrong data value can cause applications to fail or even render your system unstable. Always have a full backup of your system and back up the specific key you are modifying (REG EXPORT) before running any script that writes to the registry.

The Core Command: REG ADD​

The REG ADD command is the primary function within the REG.EXE utility for adding new keys and, more commonly, for adding or modifying values within a key.

  • If you specify a value that already exists, REG ADD will overwrite its data.
  • If the key path you specify does not exist, REG ADD will create it automatically.

The Syntax Explained​

The full syntax for adding a value is:

REG ADD "KeyName" /v "ValueName" /t DataType /d "Data" /f
  • "KeyName": (Required) The full path to the registry key you want to modify (e.g., HKCU\Software\MyApp).
  • /v "ValueName": (Required) The name of the value you want to set.
  • /t DataType: (Required) The type of data. The most common are REG_SZ (string) and REG_DWORD (number).
  • /d "Data": (Required) The data you want to assign to the value.
  • /f: (Essential for Scripts) Forces the overwrite without prompting if the value already exists.

Basic Example: Creating a Simple String Value​

This script creates a new value named LastUser inside an application's settings key to store the name of the current user.

@ECHO OFF
REM This doesn't require admin rights because it's in HKCU.

SET "RegKey=HKEY_CURRENT_USER\Software\MyCoolApp\State"
SET "ValueName=LastUser"
SET "ValueData=%USERNAME%"

ECHO --- Writing to the Registry ---
ECHO Key: %RegKey%
ECHO Value: %ValueName% = %ValueData%
ECHO.

REG ADD "%RegKey%" /v "%ValueName%" /t REG_SZ /d "%ValueData%" /f

IF %ERRORLEVEL% EQU 0 (
    ECHO [SUCCESS] The registry value was set successfully.
) ELSE (
    ECHO [FAILURE] An error occurred.
)
note

This command ensures the key HKCU\Software\MyCoolApp\State exists, and then it creates or overwrites the LastUser value with the current user's name.

Working with Different Data Types (REG_SZ, REG_DWORD)​

You must specify the correct data type for the value you are setting.

Data Type: REG_SZ (String )​

This is for any plain text value. The data should be enclosed in quotes if it contains spaces.

REG ADD "HKCU\Software\MyApp" /v "InstallPath" /t REG_SZ /d "C:\Program Files\My App" /f

Data Type: REG_DWORD (32-bit Number)​

This is for integer values. The data can be a decimal number (e.g., 100) or a hexadecimal value (e.g., 0xff).

REM This sets the value to the decimal number 1.
REG ADD "HKCU\Software\MyApp" /v "EnableLogging" /t REG_DWORD /d 1 /f
note

Other common types include REG_BINARY for binary data and REG_EXPAND_SZ for strings that contain environment variables.

Common Pitfalls and How to Solve Them​

Problem: "Access is denied."​

This is the number one cause of failure. It means your script does not have the necessary permissions to write to the specified registry key.

Solution: This almost always happens when writing to HKEY_LOCAL_MACHINE (HKLM). To modify HKLM, you must run your script as an Administrator. Writing to HKEY_CURRENT_USER (HKCU) typically does not require elevation.

Problem: The Confirmation Prompt Halts the Script​

If you try to overwrite an existing value without the /f switch, REG ADD will stop and ask for confirmation.

Example of the prompt the prompt: Value LastUser exists, overwrite(Yes/No)?

This will pause your automated script indefinitely, waiting for user input.

Solution: Always Use /f in Scripts​

The /f (force) switch is essential for any non-interactive script. It automatically answers "Yes" to the overwrite prompt, ensuring your script can run from start to finish without getting stuck.

Practical Example: Setting a Custom Application Preference​

This script sets a configuration value for an application that controls its theme. This is a typical task for a deployment or user-setup script.

@ECHO OFF
SETLOCAL
REM This script should be run as an Administrator to set a system-wide setting.

SET "AppKey=HKEY_LOCAL_MACHINE\SOFTWARE\OurCompany\MainApp\UI"
SET "ThemeValue=DarkMode"
SET "ThemeData=1"

ECHO --- Configuring Application UI ---
ECHO Setting the application to use Dark Mode for all users.
ECHO.

REM --- The REG ADD command to set the DWORD value ---
REG ADD "%AppKey%" /v "%ThemeValue%" /t REG_DWORD /d %ThemeData% /f

IF %ERRORLEVEL% EQU 0 (
    ECHO [SUCCESS] The '%ThemeValue%' setting was applied.
    ECHO The application will now use Dark Mode by default.
) ELSE (
    ECHO [FAILURE] Could not write to the registry.
    ECHO Please ensure you are running this script as an Administrator.
)

PAUSE
ENDLOCAL

Conclusion​

The REG ADD command is the standard and most direct method for writing values to the registry from a batch script.

For safe and reliable registry modifications:

  1. Always run your script as an Administrator, especially when writing to HKEY_LOCAL_MACHINE.
  2. Back up the key with REG EXPORT before you make any changes.
  3. Use the full syntax: REG ADD "Key" /v "Value" /t TYPE /d "Data" /f.
  4. Always use the /f switch to make your script non-interactive.
  5. Pay close attention to the data **/t**ype, using REG_SZ for text and REG_DWORD for numbers.

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