How to get the content of a DOS variable?

just a little clarification.....

the errorlevel variable should not be changed manually (not even in a bat) because otherwise it won't return anything afterwards......

only the system should change it....
when errorlevel is different from 0 it means there was an error.....

only zero indicates proper functioning!!!

donotadventurersunderDOS!

I also believe that this variable contains the value of the last executed "process". It seems that multiple programs can update this variable. Therefore, we need to quickly retrieve the value inserted by the software we want to "examine".
In any case, your help has allowed me to get out of this call. Thank you all.
Just a little response to "padaventuriersousDOS", it has been ages since I last used such commands but I swear on the bible (of DOS of course) that I did such things a few years ago ;-o
THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU

if you are in a bat
you do echo "%ERRORLEVEL%"
or something to test
IF "%ERRORLEVEL%" == "1" goto full
IF "%ERRORLEVEL%" == "0" goto broot
:full
echo "it works"
goto END

:broot
echo "FUCK SHIT IT CRASHES"
goto END
:END

Yahoooo! It works! Thank you, it's only the second % that I was missing!

You see I'm good after all.
Here's a thing
to assign a value to a variable based on a result
for example under Unix you do:
a command generates the result in a text file toto.txt
I do
set NAME=`cat toto.txt`
my variable NAME is equal to the result of the command cat toto.txt
cat is like type under DOS.
but under DOS I'm a bit in trouble so here’s how I do it in .bat
FOR /F %%i in (toto.txt) do set NAME=%%i
it's useful, right?
PS: see the help for for and set.

I must say that you are AMAZING. This has helped me make some progress on my test. I am now looking for the corresponding values assigned to errorlevel!
In any case, I thank you very much.
Rondbleu