DOS Batch File

What is a Batch file?

A Batch file (.bat or .cmd) is a script file used in DOS, OS/2, and Microsoft Windows operating systems that contains a series of commands to be executed by the command-line interpreter. Batch files automate repetitive tasks, system administration operations, and application launches by executing multiple commands sequentially. These files are fundamental to Windows system administration and automation, providing a simple way to script operations without requiring complex programming knowledge.

More Information

Batch files have their origins in the early days of DOS (Disk Operating System), developed by Microsoft in the 1980s. The concept was inherited from earlier operating systems where batch processing was used to execute a series of jobs without manual intervention. As Windows evolved from DOS, batch file functionality was preserved and enhanced, maintaining backward compatibility while adding new features and capabilities.

The simplicity of batch files makes them accessible to system administrators, power users, and developers who need to automate Windows-based tasks. While more powerful scripting languages like PowerShell have been introduced, batch files remain relevant due to their ubiquity, simplicity, and guaranteed presence on every Windows system. They serve as the foundation for many automated processes, software installations, and system maintenance tasks.

Batch File Format

Batch files use a straightforward command-based syntax:

Basic Structure

• Commands - DOS/Windows commands executed sequentially
• Parameters - %1, %2, %3, etc. for command-line arguments
• Variables - Environment variables with %VARIABLE% syntax
• Labels - :label for goto statements and subroutines
• Comments - Lines starting with REM or ::
• Control structures - IF, FOR, GOTO statements

Key Features

• Command execution - Run any command-line program or utility
• Conditional logic - IF/ELSE statements for decision making
• Loops - FOR loops for iteration
• Error handling - Check error levels and command success
• Environment manipulation - Set and modify environment variables
• File operations - Copy, move, delete, and process files

Variables and Parameters

• Command-line parameters - %0 (script name), %1-%9 (arguments)
• Environment variables - %PATH%, %USERNAME%, %COMPUTERNAME%
• Custom variables - SET MYVAR=value
• Special variables - %CD% (current directory), %DATE%, %TIME%
• Variable expansion - Delayed expansion with !VARIABLE!

Example Batch Script

@echo off
REM =====================================================
REM System Backup and Maintenance Script
REM Author: System Administrator
REM Date: %DATE%
REM Description: Automated backup and cleanup operations
REM =====================================================

setlocal enabledelayedexpansion

:: Configuration variables
set BACKUP_SOURCE=C:\Important\Data
set BACKUP_DEST=D:\Backups
set LOG_FILE=%BACKUP_DEST%\backup_log.txt
set MAX_LOG_SIZE=1048576
set RETENTION_DAYS=30

:: Color codes for output
set RED=[91m
set GREEN=[92m
set YELLOW=[93m
set BLUE=[94m
set NC=[0m

:: Check if running as administrator
net session >nul 2>&1
if %errorLevel% == 0 (
    echo %GREEN%Running with administrator privileges%NC%
) else (
    echo %RED%Error: This script requires administrator privileges%NC%
    echo Please run as administrator
    pause
    exit /b 1
)

:: Create backup directory if it doesn't exist
if not exist "%BACKUP_DEST%" (
    echo %YELLOW%Creating backup directory: %BACKUP_DEST%%NC%
    mkdir "%BACKUP_DEST%" 2>nul
    if !errorlevel! neq 0 (
        echo %RED%Error: Failed to create backup directory%NC%
        goto :error_exit
    )
)

:: Function to log messages
:log_message
echo [%DATE% %TIME%] %~1 >> "%LOG_FILE%"
echo %~1
goto :eof

:: Check disk space
call :log_message "%BLUE%Checking available disk space...%NC%"
for /f "tokens=3" %%a in ('dir /-c "%BACKUP_DEST%" ^| find "bytes free"') do set FREE_SPACE=%%a
set /a FREE_SPACE_GB=!FREE_SPACE!/1073741824
if !FREE_SPACE_GB! lss 5 (
    call :log_message "%RED%Warning: Less than 5GB free space available%NC%"
) else (
    call :log_message "%GREEN%Available space: !FREE_SPACE_GB! GB%NC%"
)

:: Create timestamp for backup folder
for /f "tokens=1-4 delims=/ " %%a in ('date /t') do set BACKUP_DATE=%%d%%b%%c
for /f "tokens=1-2 delims=: " %%a in ('time /t') do set BACKUP_TIME=%%a%%b
set BACKUP_FOLDER=%BACKUP_DEST%\Backup_%BACKUP_DATE%_%BACKUP_TIME%

call :log_message "%BLUE%Starting backup process...%NC%"
call :log_message "Source: %BACKUP_SOURCE%"
call :log_message "Destination: %BACKUP_FOLDER%"

:: Perform backup using robocopy
robocopy "%BACKUP_SOURCE%" "%BACKUP_FOLDER%" /E /COPY:DAT /R:3 /W:10 /LOG+:"%LOG_FILE%" /TEE
set ROBOCOPY_EXIT=%errorlevel%

:: Check robocopy exit code
if %ROBOCOPY_EXIT% geq 8 (
    call :log_message "%RED%Backup failed with errors (Exit code: %ROBOCOPY_EXIT%)%NC%"
    goto :error_exit
) else if %ROBOCOPY_EXIT% geq 4 (
    call :log_message "%YELLOW%Backup completed with warnings (Exit code: %ROBOCOPY_EXIT%)%NC%"
) else (
    call :log_message "%GREEN%Backup completed successfully%NC%"
)

:: Cleanup old backups
call :log_message "%BLUE%Cleaning up old backups older than %RETENTION_DAYS% days...%NC%"
forfiles /P "%BACKUP_DEST%" /M "Backup_*" /D -%RETENTION_DAYS% /C "cmd /c echo Deleting @path && rd /s /q @path" 2>nul
if !errorlevel! equ 0 (
    call :log_message "%GREEN%Old backup cleanup completed%NC%"
) else (
    call :log_message "%YELLOW%No old backups found or cleanup not needed%NC%"
)

:: System maintenance tasks
call :log_message "%BLUE%Performing system maintenance...%NC%"

:: Clear temporary files
call :log_message "Clearing temporary files..."
del /f /q "%TEMP%\*.*" 2>nul
for /d %%x in ("%TEMP%\*") do rd /s /q "%%x" 2>nul

:: Clear Windows temporary files
del /f /q "C:\Windows\Temp\*.*" 2>nul
for /d %%x in ("C:\Windows\Temp\*") do rd /s /q "%%x" 2>nul

:: Empty Recycle Bin (Windows 10/11)
PowerShell.exe -Command "Clear-RecycleBin -Force" 2>nul

call :log_message "%GREEN%System maintenance completed%NC%"

:: Generate summary report
call :log_message "%BLUE%Generating summary report...%NC%"
echo.
echo ============================================
echo           BACKUP SUMMARY REPORT
echo ============================================
echo Date: %DATE%
echo Time: %TIME%
echo Source: %BACKUP_SOURCE%
echo Destination: %BACKUP_FOLDER%
echo Free Space: !FREE_SPACE_GB! GB
echo Status: SUCCESS
echo ============================================

:: Rotate log file if too large
for %%A in ("%LOG_FILE%") do set LOG_SIZE=%%~zA
if !LOG_SIZE! gtr %MAX_LOG_SIZE% (
    call :log_message "Rotating log file (size: !LOG_SIZE! bytes)"
    move "%LOG_FILE%" "%LOG_FILE%.old" >nul 2>&1
)

call :log_message "%GREEN%All operations completed successfully%NC%"
echo.
echo Press any key to exit...
pause >nul
goto :end

:: Error handling
:error_exit
call :log_message "%RED%Script execution failed%NC%"
echo.
echo An error occurred during script execution.
echo Check the log file: %LOG_FILE%
echo.
echo Press any key to exit...
pause >nul
exit /b 1

:: End of script
:end
endlocal
exit /b 0

How to work with Batch files

Batch files can be created and executed using various tools and methods:

Text Editors

• Notepad - Simple built-in Windows text editor
• Notepad++ - Advanced text editor with syntax highlighting
• Visual Studio Code - Modern editor with batch file extensions
• Sublime Text - Lightweight editor with batch syntax support
• vim/gvim - Powerful text editor with batch file support

Execution Methods

• Double-click - Direct execution from Windows Explorer
• Command Prompt - Run from cmd.exe
• Scheduled Tasks - Automated execution via Task Scheduler
• Startup scripts - Execute during system startup
• Group Policy - Deploy via Active Directory

Development Tools

• Command Prompt - Built-in command-line interface
• Windows PowerShell ISE - Can edit and run batch files
• Batch file debuggers - Third-party debugging tools
• Error checking tools - Syntax validation utilities

Testing and Debugging

• Echo statements - Display variable values and execution flow
• Pause commands - Stop execution for inspection
• Error level checking - Validate command success
• Log files - Record execution details and errors

Common Batch File Commands

Essential commands for batch scripting:

• ECHO - Display text or toggle command echoing
• SET - Create or modify environment variables
• IF - Conditional execution
• FOR - Loop through files, directories, or lists
• GOTO - Jump to labeled sections
• CALL - Execute another batch file or subroutine
• ROBOCOPY - Advanced file copying utility
• XCOPY - File and directory copying
• DEL/ERASE - Delete files
• RD/RMDIR - Remove directories

Advanced Features

Batch files support sophisticated operations:

• Subroutines - Reusable code blocks with CALL
• Parameter passing - Arguments to subroutines
• String manipulation - Substring extraction and replacement
• Mathematical operations - Basic arithmetic with SET /A
• File parsing - Process text files line by line
• Registry operations - Read and modify Windows registry
• Service management - Start, stop, and configure Windows services

Best Practices

Writing effective batch files:

• Use @echo off - Suppress command echoing for cleaner output
• Include error checking - Validate command success with errorlevel
• Document your code - Use REM statements for comments
• Use meaningful variable names - Clear, descriptive variable names
• Handle edge cases - Check for file existence, permissions, etc.
• Test thoroughly - Test with various inputs and scenarios
• Use quotes - Quote paths and variables containing spaces

Security Considerations

Batch file security is important:

• Input validation - Validate user inputs and parameters
• Path security - Use absolute paths when possible
• Privilege management - Run with minimal required privileges
• Temporary files - Secure creation and cleanup of temp files
• Error handling - Don't expose sensitive information in errors
• Code signing - Consider signing important batch files

Common Use Cases

Batch files are commonly used for:

• System administration - User management, system configuration
• Software installation - Automated application deployment
• File management - Backup, synchronization, and organization
• System maintenance - Cleanup, defragmentation, updates
• Build processes - Compilation and deployment automation
• Environment setup - Development environment configuration
• Data processing - Batch processing of files and data
• Scheduled tasks - Automated maintenance and monitoring
• Legacy system integration - Interface with older DOS applications