CODEWITHSUNDEEP
batch-file
JJMcQuade
JJMcQuade

Reputation: 13

How to find the value of a variable in batch without knowing the name of the variable

I'm making a simple batch game, and I'm trying to find out how to use the value of a variable with an unknown name. Example:
I dont know the name or the value of the var1 variable, because it is automatically generated at an earlier point in the game.
The only thing I know is the 3rd line: set var3=var2.
I need my game to use the value of "var1" in an if statement like shown in the last line.
How would I do this?

set var1=5
set var2=var1
set var3=var2
if ??? EQU something something...

Upvotes: 1

Views: 345

Answers (1)

dbenham
dbenham

Reputation: 130819

It took a few edits, but I finally came up with a truly bullet proof option (method 5).

In method 5, if var3 is replaced by a variable name that contains " then you will have to escape some quotes. But if you are sophisticated enough to put a quote in a variable name then you already know how to do that :-)

@echo off
setlocal

set var1=5
set var2=var1
set var3=var2

::method 1 - Without using delayed expansion. (this is relatively slow and unsafe)
::           the initial expansion uses 1 % and no CALL
::           the 2nd expansion uses CALL and 2 %%
::           the 3rd expansion uses CALL and 4 %%%%
::           each additional expansion would require another CALL and doubled percents
call call set "test=%%%%%%%var3%%%%%%%
if "%test%"=="5" echo Method 1 works: Value of "unknown var"=%test%

::The remaining methods use delayed expansion. They are safer and faster.
setlocal enableDelayedExpansion

::method 2 - Using normal and delayed expansion and a temp variable.
::           Almost always works, but can fail in rare cases where variable
::           name contains "
set "test=!%var3%!"
if "!%test%!"=="5" echo Method 2 works: Value of "unknown var"=!%test%!

::method 3 - Using normal and delayed expansion without using any temp variable.
::           This works for sensible variable names, but fails if name contains
::           * or ?. Also can fail if variable name contains "
for %%A in ("!%var3%!") do if "!%%~A!"=="5" echo Method 3 works: Value of "unknown var"=!%%~A!

::method 4 - Using normal and delayed expansion without using any temp variable.
::           This almost always works, but can fail in rare cases where variable
::           name contains "
for /f "eol==delims=" %%A in ("!%var3%!") do if "!%%A!"=="5" echo Method 4 works: Value of "unknown var"=!%%A!

::method 5 - Using delayed expansion without using any temp variable.
::           This always works!
for /f "eol==delims=" %%A in ("!var3!") do for /f "eol==delims=" %%B in ("!%%A!") do if "!%%B!"=="5" echo Method 5 works: Value of "unknown var"=!%%B!

Upvotes: 2

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