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Indirect Access to Environment Variables (by reference)

You may wish to indirectly read/write to an environment variable whose name is (or can be) contained by another environment variable.

You will almost always want to do this inside a subroutine so that is what this code shows:

@echo off
setlocal ENABLEDELAYEDEXPANSION

set COUNTER=11
call :ADD1 "COUNTER"

echo TEST: COUNTERS new value is "%COUNTER%" (should be "12")
goto :EOF


@rem ### Manipulate value where only variable's name is passed #########
:Add1
    @rem *** Get Passed variable name and its value ***
    set  VarName=%~1
    set VarValue=!%VarName%!
    echo TEST: VARNAME "%VarName%" has a value of "%VarValue%"

    @rem *** Change the value (we will return it) ***
    set /a VarValue=VarValue + 1

    @rem *** "Return" the value ***
    set %VarName%=%VarValue%
    goto :EOF

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