Intro

There's a lot of advice out there for dealing with return codes in batch files (using the ERROLEVEL mechanism), e.g.

• Get error code from within a batch file
• ERRORLEVEL inside IF

Some of the advice is to do if errorlevel 1 goto somethingbad, while others recommend using the %ERRORLEVEL% variable and using ==, EQU, LSS, etc. There seem to be issues within IF statements and such, so then delayedexpansion is encouraged, but it seems to come with quirks of its own.

Question

What is a foolproof (i.e. robust, so it will work on nearly any system with nearly any return code) way to know if a bad (nonzero) code has been returned?

My attempt

For basic usage, the following seems to work ok to catch any nonzero return code:

if not errorlevel 0 (
    echo error level was nonzero
)