Common Batch Script Patterns
Most production batch files are built from a small set of recurring patterns: looping over files or lines with FOR, validating input arguments before doing real work, and branching on the exit status of the previous command. Once you recognize these shapes, you stop reinventing them from scratch and start assembling scripts from proven building blocks, which cuts down on the subtle quoting and escaping bugs that plague ad-hoc batch code.
Cricket analogy: A captain like Virat Kohli doesn't invent a new batting order every match — he reuses proven templates (anchor at three, finisher at five) the same way a scripter reuses a tested FOR loop instead of writing fragile one-off logic.
Iterating with FOR /F: Parsing Command Output and Files
The FOR /F loop is the workhorse pattern for reading text line by line, whether from a file, a quoted string, or the output of another command. The 'tokens=' and 'delims=' options let you split each line into fields — for example tokens=1,2 delims=, extracts the first two comma-separated columns into %%a and %%b. Wrapping a command in backticks (usebackq with quotes) inside the FOR /F clause is the standard idiom for capturing command output line by line without spawning a temp file, and it is the pattern behind most log-parsing and CSV-processing batch scripts.
Cricket analogy: Ravichandran Ashwin dissecting a scorecard column by column — overs, maidens, runs, wickets — to extract just the economy-rate figures mirrors FOR /F splitting a line into tokens=1,2 delims=, and grabbing only the fields you need.
@echo off
setlocal enabledelayedexpansion
rem Parse a CSV of name,score and print totals over 80
for /f "usebackq tokens=1,2 delims=," %%a in ("scores.csv") do (
set "name=%%a"
set "score=%%b"
if !score! GTR 80 (
echo !name! passed with !score!
)
)
rem Capture command output line by line
for /f "tokens=* usebackq" %%L in (`ipconfig ^| findstr /i "IPv4"`) do (
echo Found: %%L
)Argument Parsing and Default Values
Well-behaved scripts validate %1, %2, and so on before using them, and fall back to sensible defaults when arguments are missing. The idiom 'if "%~1"=="" set "MODE=default"' guards against the classic batch gotcha where an empty %1 makes the IF comparison syntactically invalid. SHIFT is the companion pattern for scripts that accept a variable number of arguments — it lets a script loop over %1 repeatedly, consuming one argument per iteration, which is how batch approximates the array-processing loops that other languages get natively. %~dp0 is the standard pattern for resolving the script's own directory so relative paths work regardless of the caller's current directory.
Cricket analogy: MS Dhoni's default field placement at the death overs — deep square leg and long-on covered by default unless the batter's tendencies dictate otherwise — mirrors setting a default MODE value when no argument overrides it.
%~dp0 always expands to the drive and path of the currently executing batch file, with a trailing backslash. Combine it with %~nx0 (name and extension) to build robust self-referential paths: 'set "SCRIPT=%~dp0%~nx0"' works no matter what directory the script was launched from.
Error Handling: ERRORLEVEL, &&/||, and GOTO :error
The idiomatic error-handling pattern in batch is to check %ERRORLEVEL% immediately after the command that might fail, since any subsequent command (including IF itself) can reset it. 'command && echo ok || echo failed' chains success and failure branches concisely for single commands, while longer sequences typically use 'if errorlevel 1 goto :error' followed by a ':error' label near the bottom of the script that prints a message and exits with 'exit /b 1'. This centralizes cleanup and messaging instead of duplicating it after every fallible command.
Cricket analogy: An umpire immediately checking the third-umpire review the moment a run-out appeal happens, before any other play resets the situation, mirrors checking %ERRORLEVEL% right after the command that might have failed.
IF itself can reset %ERRORLEVEL% to 0 on some Windows versions if the IF statement succeeds. Capture the value into a variable immediately — 'set "RC=%ERRORLEVEL%"' — before running any other command, then test %RC% instead of relying on ERRORLEVEL staying stable across multiple lines.
- FOR /F with tokens= and delims= is the standard pattern for parsing CSV lines and command output.
- Wrap commands in backticks inside FOR /F to capture their output line by line without a temp file.
- Guard against empty arguments with if "%~1"=="" before comparing %1 directly.
- SHIFT lets a script loop over an unknown number of arguments one at a time.
- %~dp0 resolves the running script's own directory for reliable relative paths.
- Capture %ERRORLEVEL% into a variable immediately after a risky command, since later commands can reset it.
- Centralize failure handling with goto :error and a labeled cleanup block instead of repeating logic.
Practice what you learned
1. In 'for /f "tokens=1,2 delims=," %%a in ("file.csv") do ...', what does %%b refer to?
2. Why should %ERRORLEVEL% be captured into a variable immediately after a command runs?
3. What does %~dp0 expand to inside a running batch script?
4. What is the purpose of checking if "%~1"=="" before using %1 in a comparison?
5. What does SHIFT do in a batch script?
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