windows batch command nested variable - windows

Question

I have a requirement to use nested variables for creating a folder based on a environment variables.
Assume I have variables listed below:
%ABC_ASIA_LOCATION%
%ABC_EUROPE_LOCATION%
%ABC_US_LOCATION%
and I want to pass the country as variable like %ABC_%COUNTRY%_LOCATION%.
How do I achieve this in Windows utilizing batch scripting?

Answer 1

you have to enclose each variable into %:
set "ABC=ABC"
set "COUNTRY=EUROPE
set "LOCATION=MUNICH
echo %ABC%_%COUNTRY%_%LOCATION%
Result: ABC_EUROPE_MUNICH
Or if you just want Country as a variable, keeping the rest fixed:
echo ABC_%COUNTRY%_LOCATION
Result: ABC_EUROPE_LOCATION
or if you want the whole thing to be a variable (a variable name containing another variable), you have to use delayed expansion:
setlocal enabledelayedexpansion
set country=EUROPE
set "ABC_EUROPE_LOCATION=a town in southern Germany"
echo !ABC_%country%_LOCATION!
which gives you: a town in southern Germany
Note: setlocal has no effect outside of batchfiles, so delayed expansion works only:
- in batchfiles
- when the command prompt was started with delayed expansion enabled (cmd /v:on) (by default, the command prompt runs with delayed expansion disabled)

Answer 2

There are times when you need the nested variable to work inside a for loop, which already requires the !varname! syntax for the variable expansion. When this is the case, !ABC_%country%LOCATION!, will not work (reference Stephan's post on 9/6/2017 at 7:24). Neither will !ABC!country!_LOCATION!.
The following batch file demonstrates this. This is a somewhat contrived example to demonstrate the issue. In the subroutine, we can also set a variable to the nested value if you didn't want to do the work in the subroutine.
#echo off
setlocal enabledelayedexpansion
setlocal
set var1=value1
set var2=value2
set var3=value3
set var4=value4
set var5=value5
for %%A in (var1 var2 var3 var4 var5) do (
set varname=%%A
echo 1.This will not work: !varname!=!!varname!!
echo 2.This will not work: !varname!=%!varname!%
echo 3.This will not work: !varname!=!%varname%!
echo 4.This will not work: %varname%=%varname%
echo 5.This will not work: %varname%=%%varname%%
call:NestedVar %%A
call:getNestedVar new%%A %%A
echo new%%A=!new%%A!
echo.
echo.
)
goto:eof
:NestedVar
echo This will work: %1=!%1! (but only if setlocal enabledelayedexpansion is used)
goto:eof
:getNestedVar
REM Use: getNestedVar newVariableName varName
REM Will set newVariableName to the value of varName
echo Setting variable, %1=!%2!
set %1=!%2!
goto:eof