Batch Files

A comprehensive skill for creating, editing, debugging, and maintaining Windows batch files (.bat/.cmd) using cmd.exe. Applies to CLI tool development, system administration automation, scheduled tasks, file operations scripting, and PATH-based executable scripts.

When to Use This Skill

• Creating or editing .bat or .cmd files
• Automating Windows tasks (file operations, deployments, backups)
• Building CLI tools intended for a bin/ folder on PATH
• Writing scheduled task scripts (SCHTASKS, Task Scheduler)
• Debugging batch script issues (variable expansion, error levels, quoting)
• Integrating batch scripts with external tools (curl, git, Node.js, Python)
• Scaffolding new batch-based projects with structured templates

Prerequisites

• Windows NT-based OS (Windows 7 or later)
• cmd.exe (built-in)
• Optional: a bin/ directory on PATH for distributing scripts as commands
• Optional: PATHEXT configured to include .BAT;.CMD (default on Windows)

Command Interpretation

cmd.exe processes each line through four stages in order:

1. Variable substitution — %VAR% tokens are replaced with environment variable values. %0–%9 reference batch arguments. %* expands to all arguments.
2. Quoting and escaping — Caret ^ escapes special characters (& | < > ^). Quotation marks prevent interpretation of enclosed special characters. In batch files, %% yields a literal %.
3. Syntax parsing — Lines are split into pipelines (|), compound commands (&, &&, ||), and parenthesized groups ( ).
4. Redirection — > overwrites, >> appends, < reads input, 2> redirects stderr, 2>&1 merges stderr into stdout, >NUL discards output.

Variables

Environment Variables

set _MY_VAR=Hello World
echo %_MY_VAR%
set _MY_VAR=

• set with no arguments lists all variables
• set _PREFIX lists variables starting with _PREFIX
• No spaces around = — set name = val sets variable "name " to " val"

Special Variables

Scoping with SETLOCAL / ENDLOCAL

setlocal
set _LOCAL_VAR=scoped value
endlocal
REM _LOCAL_VAR is no longer defined here

To return a value from a scoped block:

endlocal & set _RESULT=%_LOCAL_VAR%

Delayed Expansion

Variables inside parenthesized blocks are expanded at parse time. Use delayed expansion for runtime evaluation:

setlocal EnableDelayedExpansion
set _COUNT=0
for /l %%i in (1,1,5) do (
    set /a _COUNT+=1
    echo !_COUNT!
)
endlocal

• !VAR! expands at execution time (delayed)
• %VAR% expands at parse time (immediate)

Control Flow

Conditional Execution

if exist "output.txt" echo File found
if not defined _MY_VAR echo Variable not set
if "%_STATUS%"=="ready" (echo Go) else (echo Wait)
if %ERRORLEVEL% neq 0 echo Command failed

Comparison operators: equ, neq, lss, leq, gtr, geq. Use /i for case-insensitive string comparison.

Compound Commands

command1 & command2        & REM Always run both
command1 && command2       & REM Run command2 only if command1 succeeds
command1 || command2       & REM Run command2 only if command1 fails

FOR Loops

REM Iterate over a set of values
for %%i in (alpha beta gamma) do echo %%i

REM Numeric range: start, step, end
for /l %%i in (1,1,10) do echo %%i

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

REM Recursive file search
for /r %%f in (*.log) do echo %%f

REM Directories only
for /d %%d in (*) do echo %%d

REM Parse command output
for /f "tokens=1,2 delims=:" %%a in ('ipconfig ^| findstr "IPv4"') do echo %%b

REM Parse file lines
for /f "usebackq tokens=*" %%a in ("data.txt") do echo %%a

GOTO and Labels

goto :main_logic
:usage
echo Usage: %~nx0 [options]
exit /b 1

:main_logic
echo Running main logic...
goto :eof

goto :eof exits the current batch or subroutine. Labels start with :.

Command-Line Arguments

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