DOS ErrorLevel - How to manage errors with the exit code ?

Check the exit status of the previous command

You can test if with the if errorlevel statement:

• If error is greater than 1

if ERRORLEVEL  1 (
  echo an error occurred
  exit /B %ERRORLEVEL%
)

• or with the dynamic variable

if %ERRORLEVEL% neq 0 (
  echo an error occurred
)
REM or
if %ERRORLEVEL% equ 0 (
  echo no error occurred
)

Below is a more detailed example:

• bat files use one % to define a variable (By using 2 %, you will get then an error)

@echo off
for %%v in (*.bat) do echo %v

• Running it cause this errors to occur:

error.bat

v was unexpected at this time

• When you check the value of the ERRORLEVEL, you get:

echo %ERRORLEVEL%

9009

• You can then check this kind of error with the if errorlevel statement:

if errorlevel 9009 (echo bad variable initialization) else (echo that's all good)

bad variable initialization

• But the default operator is not an equality but a “greater than”, then this “if” statement will also work

if errorlevel 9000 (echo a bad thing occurs) else (echo that's all good)

a bad thing occurs

• You can then use a string comparison with the %errorlevel% dynamic variable

if %errorlevel% EQU 9009 (echo the error 9009 occurs) else (echo the error 9009 doesn't occurs)

the error 9009 occurs

exit a script from a subroutine ?

In a function or subroutine, the command exit /b exits only the subroutine and not the script. You need to exit the subroutine with a goto and call the exit command

(goto) 2>nul || exit /b %ERRORLEVEL%

Example of function that can be called to check the previous command execution.

:checkErrorLevel
if ERRORLEVEL 1 (
  echo "An error occurred"
  REM exit the subroutine then exit the script
  (goto) 2>nul || exit /b %ERRORLEVEL%
) ELSE (
  echo "The previous command has executed successfully"
)
goto :eof

(reinitialize|reset) it

To reinitialize it to 0 after an error, you use the exit command with the B switch in a child batch script:

For instance, with the following script named: resetErrorLevel.bat

:: This script is there just to reset the error level
exit /B 0

If you start this demo script:

@echo off
echo Before the error, the errorlevel value is: %ERRORLEVEL%
copy badfile badlocation
echo After the error, the errorlevel value is: %ERRORLEVEL%
call resetErrorLevel.bat
echo After the resetErrorLevel.bat, the errorlevel value is %ERRORLEVEL%

you will get this output:

Before the error, the errorlevel value is: 0
The system cannot find the file specified.
After the error, the errorlevel value is: 1
After the resetErrorLevel.bat, the errorlevel value is 0

End the script properly

Before the end of the script

if %ERRORLEVEL% neq 0 (
  exit /b %ERRORLEVEL%
)

where:

• Dos - Exit