Windows Batch Scripting

Windows Batch Scripting

Writing production-grade .bat/.cmd scripts for Windows automation.

Structure

@echo off
setlocal enabledelayedexpansion

REM === CONFIG ===
set "APP_NAME=MyTool"
set "LOG_FILE=%~dpn0.log"

REM === MAIN ===
call :check_admin
call :do_work
goto :eof

REM === FUNCTIONS ===
:check_admin
net session >nul 2>&1
if %errorlevel% neq 0 (
    echo Requesting admin...
    powershell -Command "Start-Process '%~f0' -Verb RunAs"
    exit /b
)
goto :eof

:do_work
echo Working...
goto :eof

Key Patterns

Argument Parsing

if "%~1"==""     echo No args & exit /b 1
if /I "%~1"=="/?"  call :help & exit /b 0
if /I "%~1"=="--help"  call :help & exit /b 0
set "ACTION=%~1"
set "TARGET=%~2"
shift /1

Error Handling

call :some_func
if %errorlevel% neq 0 (
    echo ERROR: Function failed with code %errorlevel%
    exit /b %errorlevel%
)

For Loops

REM Files in directory
for %%f in (*.txt) do echo %%f

REM Line-based (command output)
for /f "tokens=*" %%l in ('dir /b *.txt') do echo %%l

REM Delimited parsing
for /f "tokens=1,2 delims=," %%a in (data.csv) do echo %%a = %%b

REM Range
for /l %%i in (1,1,10) do echo %%i

String Operations

set "var=hello world"
echo %var:~0,5%     REM hello
echo %var:~6%       REM world
echo %var:world=there%  REM hello there
if /I "%var%"=="hello world" echo match

Delayed Expansion (important!)

setlocal enabledelayedexpansion
set "count=0"
for %%f in (*.txt) do (
    set /a count+=1
    echo !count!: %%f     REM use !var! not %%var%% inside loops
)

File/Dir Checks

if exist "C:\path\file.txt" echo exists
if not exist "C:\path\" mkdir "C:\path"
if defined MYVAR echo MYVAR is set

Admin Elevation

net session >nul 2>&1
if %errorlevel% neq 0 (
    echo Elevating...
    powershell -Command "Start-Process '%~f0' -Verb RunAs"
    exit /b
)

Common Functions

:log
echo [%date% %time%] %* >> "%LOG_FILE%"
goto :eof

:confirm
set /p ans="%* [y/N] "
if /I "%ans%"=="y" exit /b 0
exit /b 1

:die
echo FATAL: %*
pause
exit /b 1

Pitfalls

• %errorlevel% must be checked IMMEDIATELY after command -- gets overwritten
• Delayed expansion needed for !var! inside loops and if blocks
• Spaces in paths -- always quote: "C:\Program Files..."
• %~dp0 gives script directory with trailing backslash
• set /p leaves variable unchanged if user presses Enter (not empty)
• findstr is the closest to grep -- use findstr /i pattern file
• PowerShell is better for anything beyond basic scripting -- consider switching