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How to Get the Command Processor Extension Version (%CMDEXTVERSION%) in Batch Script

The Windows Command Processor (cmd.exe) has evolved over the years. With Windows 2000 and XP, Microsoft introduced "Command Processor Extensions," a set of powerful enhancements to classic commands like SET, IF, FOR, and many others. These extensions are responsible for most of the advanced features we rely on in modern batch scripting, such as delayed expansion and command-line argument parsing with tilde modifiers (%~1).

This guide will explain the special %CMDEXTVERSION% variable, which allows your script to query the version of these extensions. You will learn how to check if extensions are enabled at all, a crucial step for ensuring your script runs in a compatible environment.

What Are Command Processor Extensions?​

Command Processor Extensions are a feature of cmd.exe that significantly enhances its capabilities beyond the original MS-DOS COMMAND.COM. They are enabled by default on all modern Windows systems.

Some of the key features enabled by these extensions include:

  • IF DEFINED: Checking if a variable exists.
  • SET /A: Performing arithmetic operations.
  • SET /P: Prompting for user input.
  • FOR /F, FOR /D, FOR /R, FOR /L: The advanced looping commands.
  • Delayed Variable Expansion (SETLOCAL ENABLEDELAYEDEXPANSION).
  • Path modifiers for arguments (%~dp0, %~nx1, etc.).
  • PUSHD and POPD for directory stack management.

Without these extensions, modern batch scripting would be nearly impossible.

The %CMDEXTVERSION% Variable​

This is a built-in, read-only dynamic variable that holds the version number of the Command Processor Extensions currently in use.

  • If extensions are enabled, %CMDEXTVERSION% will expand to an integer representing the version.
    • Version 1 was introduced with Windows 2000.
    • Version 2 was introduced with Windows Vista and includes enhancements like changes to SET /A.
  • If extensions are disabled, this variable will not exist.

Basic Example: Displaying the Version​

You can easily see the version on your system with a simple ECHO command.

@ECHO OFF
ECHO The Command Processor Extension version is: %CMDEXTVERSION%

Output (on a modern Windows 10/11 system)

The Command Processor Extension version is: 2

How to Check if Extensions are Enabled​

The most practical use of this variable is to verify that the command extensions are active. A script that relies on modern features will fail if run in an environment where they have been disabled. You can check this with IF DEFINED.

@ECHO OFF
IF DEFINED CMDEXTVERSION (
    ECHO [SUCCESS] Command Processor Extensions are enabled.
    ECHO Version: %CMDEXTVERSION%
) ELSE (
    ECHO [FAILURE] Command Processor Extensions are disabled.
    ECHO This script requires command extensions to function.
)
note

On any standard Windows setup, this will report that they are enabled. An administrator can disable them via the registry or with cmd /E:OFF, but this is extremely rare.

Common Pitfalls and How to Solve Them​

The main "pitfall" is not a problem with the variable itself, but a lack of awareness of the extensions it represents. A scripter might write a script using modern commands and not understand why it fails on a legacy or highly restricted system.

  • Legacy Systems: While very rare now, an original Windows NT system might not have these extensions.
  • Disabled by Policy: A system administrator can disable extensions for security or policy reasons.
  • cmd /E:OFF: A user can manually start a cmd session with extensions turned off.

Solution: The check shown above is the definitive solution. Placing this check at the beginning of a complex script is a robust way to ensure the environment is compatible.

Practical Example: A Script Prerequisite Check​

This script is a template for a complex tool. Before it runs its main logic, it verifies that the environment is suitable by checking for command extensions.

@ECHO OFF
SETLOCAL

ECHO --- System Prerequisite Check ---
ECHO.

REM --- Check 1: Command Processor Extensions ---
IF NOT DEFINED CMDEXTVERSION (
    ECHO [FATAL ERROR] Command Processor Extensions are disabled.
    ECHO This script cannot continue. Please enable them.
    PAUSE
    EXIT /B 1
)

ECHO [OK] Command Extensions are enabled (Version: %CMDEXTVERSION%).

REM --- Check 2: Require at least Version 2 (for Vista+ features) ---
IF %CMDEXTVERSION% LSS 2 (
    ECHO [WARNING] The extension version is older than 2.
    ECHO Some advanced features may not be available.
)

ECHO.
ECHO --- All checks passed. Proceeding with main script logic. ---
ECHO.
REM (Your main script code goes here)

ENDLOCAL

Conclusion​

The %CMDEXTVERSION% variable is a simple but important tool for writing defensive and robust batch scripts. While you can generally assume that command extensions are enabled on any modern Windows system, a programmatic check is the professional way to guarantee it.

Key takeaways:

  • Command Processor Extensions are the foundation of modern batch scripting.
  • %CMDEXTVERSION% holds the version number of these extensions.
  • Use IF DEFINED CMDEXTVERSION to quickly and reliably check if the extensions are active.
  • For scripts that depend on modern features, performing this check at the beginning is a best practice to ensure compatibility and prevent unexpected errors.

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