.BAT File Format – Control flow

Blocks

A pair of parentheses groups commands, over one line or several, so that an if, else or for can take more than one. The ( must be where a command can start and the ) must be where a command can start or at the end of the last command, and both are plain characters in a quoted string.

if exist data.txt (
    echo found
    del data.txt
) else (
    echo missing
)

• The else must be on the same line as the ) that closes the if block, or on the same line as a one-line command (Microsoft: “You must use the else clause on the same line as the command after the if”). A ) on a line of its own and else on the next breaks it.
• A block is read and expanded as a whole, so %var% is not updated inside it; use delayed expansion.
• A ) inside a block must be escaped (^)) or quoted if it is part of text, as in echo File^(s^); Microsoft’s echo page gives that rule.
• Labels and :: comments inside a block are reported to be unreliable, and a :: as the last line of a block gives an error. Use rem.

if

The comparison operators are EQU equal, NEQ not equal, LSS less than, LEQ less than or equal, GTR greater than and GEQ greater than or equal. They are not case sensitive as words. When both sides are made only of digits, the strings are converted to numbers and compared as numbers (Microsoft), so 10 GTR 9 is true; otherwise they are compared as strings, so 10 GTR 9a is false. /i works with the == form as well.

• Any of the forms may be followed by else and a command or block.
• if can be nested, and &, && and || after the command belong to the command, not to the condition, so if a==a echo x & echo y runs both only when the condition is true. There is no and or or: nest the ifs, or set a variable.
• An empty or unset variable on one side breaks if %a%==x into if ==x, a syntax error. Quote both sides: if "%a%"=="x".
• Special characters in an unquoted operand, such as a space, & or a ), end it early; quote it.
• Microsoft: after if defined, the variables %errorlevel%, %cmdcmdline% and %cmdextversion% are made available.
• The errorlevel form compares with the code left by the last program; %errorlevel% read inside a block shows the value from when the block was read.

if /i "%1"=="help" goto usage
if not defined LIB set LIB=C:\lib
if %errorlevel% geq 2 (echo failed) else (echo ok)
if exist "%~dp0data\*.txt" echo text files here

for

All the forms are for {%%|%}variable in (set) do command. Use %% in a batch file and % at the prompt. The variable is one character, case sensitive, and any character except 0 to 9 (so it is not mistaken for an argument); letters are the norm. No more than 52 can be active at once. in and do are required words, not parameters (Microsoft). The command can be a block.

for /f options

The options are in one quoted string, separated by spaces:

• Empty lines are skipped. A line with no token wanted gives no pass.
• In a "string" set, the symbols \ & | > < ^ are ordinary characters (Microsoft).
• A command in a for /f set that holds a pipe or redirection needs a caret before it: 'dir ^| find "x"', because the set is parsed once for the for and again for the child interpreter.
• The output of the command is captured in memory and parsed as if it were a file.

Variable modifiers

A for variable accepts the same ~ modifiers as the batch arguments: %%~I (no quotes), %%~fI, %%~dI, %%~pI, %%~nI, %%~xI, %%~sI, %%~aI, %%~tI, %%~zI, %%~$PATH:I and the combinations %%~dpI, %%~nxI, %%~fsI, %%~dp$PATH:I, %%~ftzaI. See the table. A valid variable name ends the %~ syntax, so an upper-case variable name keeps it readable (Microsoft).

rem every .txt file, each folder, and each line of a file
for %%f in (*.txt) do echo %%~nxf
for /d %%d in (C:\Users\*) do echo %%~nxd
for /r "C:\src" %%f in (*.c) do echo %%~ftzf
for /l %%n in (10,-2,0) do echo %%n
for /f "usebackq skip=1 tokens=1,2* delims=, " %%a in ("data file.csv") do echo %%a / %%b / %%c
for /f "delims=" %%l in ('type "%~f0" ^| find /c /v ""') do set lines=%%l

Loops without for

A counted or open loop is a label, a test and a goto:

set i=0
:again
set /a i+=1
echo Pass %i%
if %i% lss 5 goto again

Inside one parenthesised block this needs setlocal enabledelayedexpansion to see the changing value. A for /l loop with a block runs the whole body in one pass and goto out of it ends the loop.

Not described