Batch
Best practices
@echo off(disable echo by default)- when setting variables surround whole statement with quotes
set "var=value"(this handles spaces and other special characters better) - Better not handle passwords, if you really need to see #Handle passwords
- surround whole script with
setlocalandendlocal(to not pollute the variable space) - Use these instead of hard-coded paths: #Useful Windows variables
for %%a in (%*) do (set "%%a=1")is the simplest parser for flags- Keep conditions (if/else) to a minimum (many pitfalls: brackets may break comments, variables are expanded only once, code becomes less linear, etc. - goto avoids some of these, but makes the code even less linear)
Cheatsheet
echo
:: turn off echoing all commands executed
@echo off
:: @-symbol: run one command without echo
@set somevar=1
:: echo Text and variable
echo Hello, %username%
:: Blank line
echo.
:: echo message with brackets need escaping when in if/for
if condition (echo text ^(hint^))
rem This is a comment
:: This is also a comment, but causes problems in if/for blocks
:: see: https://www.robvanderwoude.com/comments.php
Variables
Set
:: set without %, use surrounded with %
:: if value contains spaces, surround whole statement with ""
set "var=path\to\exe --whatever"
echo %var%
:: Prints: path\to\exe --whatever
:: if only value is surrounded, "" will become part of value
:: value of %var% will be baked into %var2% at this point
set var2="pre\%var%"
echo %var2%
:: Prints: "pre\path\to\exe --whatever"
:: numeric vars (val == 6)
set /A val=3+3
:: promt user input
set /P "uservar=just a comment, will be overwritten"
:: set multiple vars
:: make sure to use "" else space before & will be included in value
set "foo=bar" & set "poo=bear"
Compare
:: Surround var to ensure correct behavior
:: use "" if value cannot contain " (or it will error)
:: use [] if value cannot contain spaces
:: do not use single quotes ''
%var%==true
[%var%]==[some text]
"%1"=="-h & shift"
"%1" NEQ ""
"%foo%" EQU "%bar%"
:: numeric comparisons
:: LSS, LEQ, GTR, GEQ
if (3 gtr 1) (echo true)
if ("B3" gtr "b2") (echo compares char by char, case-insensitive, b>a)
Test existance
:: no % signs!
if defined var (echo yay) else (echo nay)
:: for arguments save to temp var first:
set "var=%~1"
:: Test for existance of foo (not test!)
set test=foo
if not defined %test% (echo foo not defined)
:: alternative (test if empty)
if "%~1"=="" (echo not defined or empty)
Replace and Substring
:: Replace "to" with "from"
set var3=%var:to=from%
:: Substring -> th\to\exe --whatev
set var4=%var:~2,-2%
:: Remove spaces
set var5=%var:=%
:: Remove quotes
set "var6=%var:"=%"
Useful Windows variables
Recognized environment variables - Windows Deployment | Microsoft Learn
%userprofile% -> C:\Users\schaja
%homepath% -> \Users\schaja
%username% -> schaja
%appdata% -> C:\Users\schaja\AppData\Roaming
%tmp% -> C:\Users\schaja\AppData\Local\Temp
%systemroot% -> C:\Windows
%programfiles% -> C:\Program Files
%programfiles(x86)% -> C:\Program Files (x86)
Arguments / Command Line Parameters
file.bat "C:\path\to\big file.exe" otherfile.wav -foo
%0 -> file.bat
%1 -> "C:\path\to\big file.exe"
%~1 -> C:\path\to\big file.exe [quotes removed]
%~d1 -> C:
%~n1 -> big file
%~p1 -> \path\to\
%~x1 -> .exe
%~a1 -> --a-------- (file attributes)
%~t1 -> 30.08.2021 13:42 (last change date)
%~z1 -> 1823 (file size in bytes)
%~dp1 -> C:\path\to\ (combination of d and p parameters)
%~f1 -> C:\path\to\big file.exe
%f1 -> f1 [needs tilde]
%2 -> otherfile.wav
%~2 -> otherfile.wav
%~d2 -> [current drive]
%~p2 -> [path to current folder]
%~f2 -> [drive+Path to current folder]\otherfile.wav
%3 -> -foo
%* -> "path/to/big file.exe" otherfile.wav -foo
Dropping files
When dropping a file onto a batch file (in Windows Explorer), the batch is called with the path to the dropped file as first argument %1 (similar to how exes behave).
Spaces
Paths values with spaces in them need to be quoted, otherwise they will be split into multiple arguments.
Special values and PowerShell
Values with a = in them have to be quoted as well. If the batch script is executed from a PowerShell both single and double quotes are necessary! '"foo=bar"'
for loop
:: Variable name in loop has to be one letter
:: but must not conflict with path parameters (see above)
:: Loop over integer (start=1, increment=2, end<=100)
for /l %%i in (1, 2, 100) do (echo %%i)
:: Loop over all files (no folders) in current directory and subdirectories
for /r %%a in (*) do (echo %%a)
:: Loop over all folders is current directory
for /D %%a in (*) do (echo %%a)
:: Loop over all arguments
:LoopArgs
if [%1]==[] (goto AfterLoop)
if [%1]==[-h] (goto PrintHelp)
if [%1]==[-i] (set "target=%2" & shift)
shift
goto LoopArgs
:AfterLoop
:: Loop over arguments as flags and set variables
:: .\file.bat compile run -> %compile%=="1", %run%="1"
for %%a in (%*) do (set "%%a=1")
:: Read file line by line
for /f "tokens=*" %%a in (%file%) do (echo %%a)
:: Read file properties (see arguments above)
for %%a in (%file%) do (echo %%~ta)
:: for i in ('where cmake.exe') do (echo i in ('powershell -command "$password = Read-Host -AsSecureString -Prompt 'Enter password'; $plainPassword = [System.Runtime.InteropServices.Marshal]::PtrToStringAutoSecureStringToBSTR($password)); Write-Output $plainPassword"' do (
set "password=i in (*) do set LIST=%LIST% %%i
:: LIST is just last file found
set _html=Hello^>World
echo %_html%
:: creates a file called World
set /p "var="
:: enter Hello^World!
echo %var%
:: prints HelloWorld!
setlocal EnableDelayedExpansion
set VAR=before
if "%VAR%" == "before" (
set VAR=after
if "!VAR!" == "after" @echo If you see this, it worked
)
set LIST=
for %%i in (*) do set LIST=!LIST! %%i
:: LIST contains all files
set _html=Hello^>World
echo !_html!
:: Prints normally
set /p "var="
:: enter Hello^World!
echo %var%
:: prints Hello^World!
endlocal
EnableDelayedExpansion - Windows CMD - SS64.com
batch file - How do SETLOCAL and ENABLEDELAYEDEXPANSION work? - Stack Overflow
Pitfalls of EnableDelayedExpansion
- ! in strings will need to be escaped
echo "Hello World^!"
- every line with a ! on it in the batch will lead to any carets on that line being treated as escape chars
echo "^^Hello^World!foo^^^bar"
:: Prints "^^Hello^World!foo^^^bar"
setlocal EnableDelayedExpansion
echo "^^Hello^World!foo^^^bar"
:: Prints "^HelloWorldfoo^bar"
endlocal
- handling filenames with ! in them in a for loop will fail, because the string will be interpreted as a variable name
- same goes for the usual way of masking passwords using powershell, since a for loop is used a password with ! in them will not be passed properly
Tidbits
title My cool window title
pause
Execution order
parsing - How does the Windows Command Interpreter (CMD.EXE) parse scripts? - Stack Overflow
Phase 0) Read Line:
Phase 1) Percent Expansion:
Phase 2) Process special characters, tokenize, and build a cached command block: This is a complex process that is affected by things such as quotes, special characters, token delimiters, and caret escapes.
Phase 3) Echo the parsed command(s) Only if the command block did not begin with @, and ECHO was ON at the start of the preceding step.
Phase 4) FOR %X variable expansion: Only if a FOR command is active and the commands after DO are being processed.
Phase 5) Delayed Expansion: Only if delayed expansion is enabled
Phase 5.3) Pipe processing: Only if commands are on either side of a pipe
Phase 5.5) Execute Redirection:
Phase 6) CALL processing/Caret doubling: Only if the command token is CALL
Phase 7) Execute: The command is executed