Batch-Files

# 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

| Variable | Value |

|----------|-------|

| `%CD%` | Current directory |

| `%DATE%` | System date (locale-dependent) |

| `%TIME%` | System time HH:MM:SS.mm |

| `%RANDOM%` | Pseudorandom number 0–32767 |

| `%ERRORLEVEL%` | Exit code of last command |

| `%USERNAME%` | Current user name |

| `%USERPROFILE%` | Current user profile path |

| `%TEMP%` / `%TMP%` | Temporary file directory |

| `%PATHEXT%` | Executable extensions list |

| `%COMSPEC%` | Path to cmd.exe |

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 comm