3. `for /F` Deep Dive¶

What & why¶

for /F is how batch reads and parses text: files, strings, and — most importantly — the output of other commands. It's how you capture command results into variables, which the language otherwise can't do. It has five options and several sharp edges.

The three sources¶

rem 1. A file (or files):
for /F %%L in (data.txt) do ...

rem 2. A literal string (in quotes):
for /F %%L in ("one two three") do ...

rem 3. A command's output (in single quotes):
for /F %%L in ('dir /b *.txt') do ...

The options string¶

for /F "tokens=1,3 delims=,; skip=1 eol=# usebackq" %%a in (...) do ...

Option	Meaning
`delims=xyz`	characters that separate tokens (default: space + tab)
`tokens=n,m`	which token(s) to hand to the loop variable(s)
`skip=n`	ignore the first `n` lines
`eol=c`	lines starting with `c` are treated as comments and skipped (default: `;`)
`usebackq`	change the quoting rules (see below)

`tokens=`¶

Each requested token goes into a successive loop variable, starting from the one you named:

rem name is %%a, so token 1->%%a, token 3->%%b
for /F "tokens=1,3 delims=," %%a in ("alice,30,london") do echo %%a in %%b

rem ranges:
for /F "tokens=1-3" %%a in ("x y z w") do echo %%a %%b %%c    &rem x y z

rem "the rest": * grabs everything after the last numbered token
for /F "tokens=1,2*" %%a in ("verb noun the rest of the line") do (
    echo verb=%%a noun=%%b rest=%%c
)

tokens=* = the whole line with leading delimiters stripped. tokens=1,* = first token, then the remainder including its internal spacing.

`delims=`¶

rem Split on comma only:
for /F "tokens=1-3 delims=," %%a in ("a, b ,c") do echo [%%a][%%b][%%c]
rem -> [a][ b ][c]   (spaces are NOT delimiters here — only comma is)

rem Split on comma OR semicolon OR space:
for /F "tokens=1-3 delims=,; " %%a in ("a;b c") do echo %%a %%b %%c

delims= must usually be last in the options string (a trailing space in delims= would otherwise swallow the next option). To split on nothing (whole line, no tokenising), use delims= as the final option:

for /F "usebackq delims=" %%L in ("file with spaces.txt") do echo LINE: %%L

`skip=` and `eol=`¶

rem Skip a header row:
for /F "skip=1 tokens=1,2 delims=," %%a in (people.csv) do echo %%a=%%b

rem Ignore lines starting with #:
for /F "eol=# tokens=1,2 delims== " %%k in (config.ini) do set "cfg_%%k=%%l"

eol is a single character and only matches at the very start of a line. There's no multi-char or mid-line comment support.

`usebackq`¶

Changes quoting so you can use quoted filenames and still run commands:

Without `usebackq`	With `usebackq`
`("literal string")`	`('literal string')` ... no: string is `"..."`, still
`('command')`	(`command`) — backticks run a command
`(filename)` unquoted only	`("quoted filename")` allowed

Practical rule: use usebackq whenever your filename needs quotes, and then run commands with backticks:

for /F "usebackq delims=" %%L in ("C:\My Files\list.txt") do echo %%L
for /F "usebackq tokens=2" %%a in (`hostname`) do set "host=%%a"

Capturing command output into a variable¶

The idiom you'll use constantly:

for /F "delims=" %%v in ('git rev-parse --short HEAD') do set "commit=%%v"
echo Building commit %commit%

Multi-line output — last line wins unless you accumulate:

set "n=0"
for /F %%v in ('tasklist /fi "imagename eq notepad.exe" /nh') do set /a n+=1

Escaping inside `('...')`¶

The command runs through cmd, so |, >, <, & inside must be caret-escaped:

for /F "tokens=2 delims=:" %%a in ('ipconfig ^| findstr /i "IPv4"') do set "ip=%%a"
for /F "delims=" %%f in ('dir /b /s *.log ^| findstr /v "archive"') do echo %%f

And % inside the command must be %% (script) as usual.

Reading a file safely¶

setlocal EnableDelayedExpansion
set "count=0"
for /F "usebackq tokens=* delims=" %%L in ("%~dp0input.txt") do (
    set /a count+=1
    set "line[!count!]=%%L"
)
echo Read !count! lines.

Empty lines are skipped

for /F silently ignores blank lines. If line numbers matter, pipe through findstr /n "^" to prefix every line with N: (which also protects lines that would otherwise be skipped), then strip the prefix:

for /F "usebackq delims=" %%L in (`findstr /n "^" "%~dp0input.txt"`) do (
    set "raw=%%L"
    set "raw=!raw:*:=!"      &rem drop the "N:" prefix
    echo !raw!
)

Common mistakes¶

'single quotes' vs "double" vs (bare) — single = run a command, double = literal string, bare = filename. Mixing them up is the #1 error.
Quoted filename without usebackq — treated as a literal string to parse, not a file.
delims= not last — options after it get eaten.
Blank lines vanishing — use the findstr /n "^" trick.
Lines starting with ; disappearing because that's the default eol. Set eol= to something impossible, or accept it.
Unescaped | / > inside ('...') — The process tried to write to a nonexistent pipe or worse.
tokens=1,2,3 giving you %%a %%b %%c but you only declared %%a — that's fine, it auto-allocates %%b, %%c; just don't collide with an outer loop's letters.
Long lines — for /F truncates lines at ~8192 bytes.
Unicode / UTF-16 files — for /F expects ANSI/OEM; UTF-16 comes through as garbage. Convert first (type won't help; use PowerShell).

Exercises¶

Read config.ini (lines like key = value, # comments, blank lines) into variables named cfg_<key>. Print them all afterward.
Capture whoami /groups and count how many groups you're in.
Parse ipconfig output to extract your IPv4 address and default gateway into two variables.
Given a CSV with a header, skip=1 it and print row N: <col1> / <col3> for each data row, with correct row numbers (mind the blank-line problem).
Read a file preserving blank lines and exact content using the findstr /n "^" technique; write it back out to a copy and fc the two files.
Use for /F with usebackq and a backtick command to store git branch --show-current in a variable; handle the "not a git repo" case with 2^>nul and a fallback.

Recap¶

Sources: (file), ("string"), ('command') — and with usebackq: ("file"), ('string'), (`command`).
Options: tokens= (which fields, * = the rest), delims= (separators, put it last), skip= (header lines), eol= (comment char), usebackq (quoting mode).
for /F ... in ('cmd') do set "x=%%v" is how you capture command output.
Escape | > < & as ^| ^> ^< ^& inside ('...').
Blank lines are dropped — use findstr /n "^" when they matter.

Next: Error handling & exit codes →

3. for /F Deep Dive¶