Why unload variables in Windows batch files

Solution 1:

SET will set a global environment variable. It will persist after the execution of your script.

Let's have a look at an example.
First, I clear the variable to make sure it doesn't exist.

C:\Users\Oliver\Desktop>set TEST=

A quick test:

C:\Users\Oliver\Desktop>echo %TEST%
%TEST%

Let's create that batch file and execute it:

C:\Users\Oliver\Desktop>echo set TEST=something>test.bat
C:\Users\Oliver\Desktop>test.bat
C:\Users\Oliver\Desktop>set TEST=something

Let's see the value of TEST after the execution of my .bat file:

C:\Users\Oliver\Desktop>echo %TEST%
something

So, yes, clearing the variable at the end of the script is good practice.

Even better would be to use SETLOCAL and ENDLOCAL to avoid the whole problem.

Here, I created a new .bat file that uses SETLOCAL and ENDLOCAL:

C:\Users\Oliver\Desktop>type test.bat
setlocal
set TEST=something
endlocal

Let's clear TEST and echo it to make sure we start clean:

C:\Users\Oliver\Desktop>set TEST=
C:\Users\Oliver\Desktop>echo %TEST%
%TEST%

Great, now let's run the new .bat:

C:\Users\Oliver\Desktop>test.bat
C:\Users\Oliver\Desktop>setlocal
C:\Users\Oliver\Desktop>set TEST=something    
C:\Users\Oliver\Desktop>endlocal

Now TEST will still be empty:

C:\Users\Oliver\Desktop>echo %TEST%
%TEST%