Bat обработка ошибок

Every scripting and programming language contains an error handler like Java contains try-catch for error handling. In a Batch script, there is no direct way to do this, but we can create an error handler in the Batch script using a built-in variable of the Batch script name %ERRORLEVEL%.

This article will show how we can create a Batch script to handle errors and failures. Also, we are going to some examples that make the topic easier.

Error Handling in Batch Script

When a command successfully executes, it always returns an EXIT CODE that indicates whether the command successfully executed or failed to execute. So, to create an error handling in a Batch file, we can use that EXIT CODE in our program.

You can follow below general format to create an error handler:

@Echo off
SomeCommand && (
  ECHO Message for Success
) || (
  ECHO Message for Failure or Error
)

We can also do that by checking the variable named %ERRORLEVEL%. If the variable contains a value not equal to 0, then there might be a problem or error when executing the command. To test the %ERRORLEVEL% variable, you can follow the below example codes:

@ECHO off
Some Command Here !!!
IF %ERRORLEVEL% NEQ 0 (Echo Error found when running the command &Exit /b 1)

You must note that the keyword NEQ means Not Equal. And the variable %ERRORLEVEL% will only contain a non-zero value if there is a problem or error in the code.

An Example That Contains Errors

Below, we shared an example. We will run a Batch file named Your_file.bat from a location.

We intentionally removed that file from the directory. So it’s an error command.

The code for our example will be:

@echo off
ECHO Running a Batch file
CD G:\BATCH\
CALL Your_file.bat
IF  errorlevel 1 GOTO ERROR
ECHO The file run successfully.
GOTO EOF

:ERROR
ECHO The file didn't run successfully.
CMD /k
EXIT /b 1

:EOF

Now, as the file doesn’t exist in the directory, it will show an error, and you will get the below output when you run the code shared above.

Output:

Running a Batch file
The system cannot find the path specified.
'Your_file.bat' is not recognized as an internal or external command,
operable program or batch file.
The file didn't run successfully.

An Error-Free Code Example That Runs Successfully

In the example above, we made a mistake on the code intentionally to understand how the code works. If we correct it like below:

@echo off
ECHO Running a Batch file
CALL "G:\BATCH\Yourfile.bat"
IF  errorlevel 1 GOTO ERROR
ECHO The file runs successfully.
GOTO EOF

:ERROR
ECHO The file didn't run successfully.
CMD /k
EXIT /b 1

:EOF

Then we will get an output like this:

Running a Batch file
This is from the first file
The file runs successfully.

Remember, all commands we discussed here are only for the Windows Command Prompt or CMD environment.

I am just starting to learn how to script. I’m trying to understand how the system handles Error Levels and how they can be used in error handling. I know there is a difference between the environment variable %ERRORLEVEL% and the Error Level of the system. If I understand this correctly, then the
If ERRORLEVEL 1
code would check the environment variable before it checks the error level of the previous command.

So, in my program I am trying to interface a startup/stop script that will start/stop all scripts of a given machine (for testing I’m just using one application notepad.exe as an example). I have two wrapper scripts that will either start up or stop the applications by passing arguments to the independent script. If there is an error in the independent script, it will set the errorlevel using the
EXIT /B n

command. Once control is returned to the calling script, it will go to an error handling script if the exit status is non-zero.

At first I was setting the %ERRORLEVEL% to zero manually and then testing for an error after a START or TASKKILL command. But then I read that clearing %ERRORLEVEL% with
SET ERRORLEVEL=
is a better method. My issue comes in when I try to start the app with

START "" notepad.exe

Whenever I test the errorlevel after this command it is always greater than or equal to 1 unless I use SET ERRORLEVEL=0 before I run the start command. I have inserted the code for the four scripts below. Any insight and advice would be greatly appreciated.

appstart.bat:

@echo off
:: Script for application Start
set ERRORLEVEL=
:: ****
:: Additional Batch files will be executed from within this file
:: Example: 
::     Call Appbat01.bat
:: The called batch file should set ERRORLEVEL non-zero if error
:: ****

call test.bat -start
if ERRORLEVEL 1 (call error.bat) 
echo.
echo Control was returned to appstart.bat...
:: **** End Calls
goto end

:end

appstop.bat:

@echo off
:: Script for application Start
set ERRORLEVEL=
:: ****
:: Additional Batch files will be executed from within this file
:: Example: 
::     Call Appbat01.ba
:: The called batch file should set ERRORLEVEL non-zero if error
:: ****

call test.bat -stop
if ERRORLEVEL 1 (call error.bat) 
echo.
echo Control was returned to appstop.bat...
:: **** End Calls
goto end

:end

test.bat:

@echo off
if "%1"=="-start" goto :start
if "%1"=="-stop" goto :stop
goto wrongParams

:start
::****
:: Insert start up stripts here...
:: If there is an error, set ERRORLEVEL=1
::****
    set ERRORLEVEL=0
    echo.
    echo ********
    echo starting the service...
    echo.
    ::start "" "C:\Program Files\Microsoft Office\office11\winword.exe"
    start notepad.exe
    if ERRORLEVEL 1 goto error
    qprocess notepad.exe
    echo *Start.success* ERRORLEVEL is: %ERRORLEVEL%
    echo.
    goto end

:stop
::****
:: Insert stopping stripts here...
:: If there is an error, set ERRORLEVEL>1
::****
    set ERRORLEVEL=0
    echo.
    echo ********
    echo stopping the service...
    echo.
    qprocess notepad.exe 
    taskkill /f /im notepad.exe
    if ERRORLEVEL 1 goto noProcess
    goto end

:noProcess
    set ERRORLEVEL=2
    echo *noProcess* ERRORLEVEL is now: %ERRORLEVEL%
    echo.
    exit /b 2
:error
:: Errorhandler. Log application status and cause of error here. Set
:: ERRORLEVEL > 1 before returning to caller. 
    set ERRORLEVEL=1
    echo.
    echo **** Error handler inside test.bat ****
    echo.
    echo *error* ERRORLEVEL is now: %ERRORLEVEL%
    echo.
    exit /b 1

:wrongParams
:: Output an error if the wrong parameters were passed to this script.
:: Maybe try to self correct the parameter...
    set ERRORLEVEL=1
    echo.
    echo '%1' is an invalid parameter.
    echo Usage: %0 [-stop ^| -start] 
    echo *wrongParams* ERRORLEVEL is now: %ERRORLEVEL%
    echo.
    exit /b 1
:end

error.bat:

@echo off
echo **** You have reached error.bat ****
echo ERRORLEVEL inside of error.bat is: %ERRORLEVEL%
echo.
::*** Handle error...***
goto error%ERRORLEVEL%

:error2
    echo The process could not be stopped for some reason.
    goto end
:error1
    echo The process had an error in start up.
::***                ***
    goto end

:end