07-Reusable-Blocks.md

1. ✅ Use Subroutines (Labels + CALL)

   The most straightforward way to create reusable code in a batch file is using a subroutine.

   @ECHO OFF
   CALL :PrintHeader "Disk Check Utility"
   CALL :PrintHeader "Log Cleaner"
   
   GOTO :EOF
   
   :PrintHeader
   ECHO.
   ECHO ============================
   ECHO      %1
   ECHO ============================
   ECHO.
   EXIT /B

   🔍 How This Is Reusable:

   • :PrintHeader can be reused to print a formatted title anywhere.
   • %1 allows passing in a dynamic value.

2. 📂 Organize Subroutines into Utility Sections

   You can build modular utility libraries at the bottom of your script.

   @ECHO OFF
   CALL :LogInfo "Script started"
   REM Your main logic here...
   CALL :LogInfo "Script ended"
   GOTO :EOF
   
   :: -------------------------------
   :: Logging Utilities
   :: -------------------------------
   :LogInfo
   ECHO [INFO] %~1
   EXIT /B
   
   :LogError
   ECHO [ERROR] %~1
   EXIT /B

   💡 Use :: or REM to group utility sections clearly.

3. 📌 External Utility Script (Reusable Across Files)

   You can create reusable .bat libraries by keeping utility subroutines in a separate file and calling it from multiple scripts.

   📁 utils.bat (only utility functions)

   @ECHO OFF
   GOTO :EOF
   
   :LogInfo
   ECHO [INFO] %~1
   EXIT /B
   
   :LogError
   ECHO [ERROR] %~1
   EXIT /B

   📁 main.bat

   @ECHO OFF
   CALL utils.bat
   CALL :LogInfo "Started main script"
   REM More logic
   CALL :LogError "Something went wrong"
   GOTO :EOF

   ⚠️ You must CALL the file and make sure it doesn't execute its own labels unless specifically called.

4. 🧪 Example: Reusable Math Operations

   @ECHO OFF
   CALL :Add 15 25 result
   ECHO Sum is: %result%
   
   CALL :Multiply 5 10 result
   ECHO Product is: %result%
   
   GOTO :EOF
   
   :Add
   SETLOCAL
   SET /A temp=%1 + %2
   ENDLOCAL & SET %3=%temp%
   EXIT /B
   
   :Multiply
   SETLOCAL
   SET /A temp=%1 * %2
   ENDLOCAL & SET %3=%temp%
   EXIT /B

   This pattern simulates returning a value via a third parameter.

• 🧱 Simulating Functions with Multiple Outputs

  Need multiple outputs? You’ll have to use multiple variable names.

  @ECHO OFF
  CALL :DivideAndRemainder 10 3 result remainder
  ECHO Quotient: %result%
  ECHO Remainder: %remainder%
  GOTO :EOF
  
  :DivideAndRemainder
  SETLOCAL
  SET /A q=%1 / %2
  SET /A r=%1 %% %2
  ENDLOCAL & (
      SET %3=%q%
      SET %4=%r%
  )
  EXIT /B

• ⚙️ Advanced: Use Dynamic Labels (Function Dispatcher)

  If you want a more abstract way to call code blocks dynamically:

  @ECHO OFF
  SET task=LogStart
  CALL :%task%
  
  SET task=LogEnd
  CALL :%task%
  
  GOTO :EOF
  
  :LogStart
  ECHO Starting process...
  EXIT /B
  
  :LogEnd
  ECHO Process complete.
  EXIT /B

  Useful for command dispatchers or menu-based systems.

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