How execute a command in batch-file if errorlevel is not zero?

Question

I created a simple batch file which would enable me to connect to the internet.
I made it this way- If the connection is successful a message is displayed stating "connection successful" using VBscript and display a message stating "connection failure" if the connection is not established. I made this using if-else statements and errorlevel command, but I am not able to display the failure message using 'errorlevel == 1' command.I mean that if there was an error in the connection process the success message is displayed instead of failure message.

Here's the code in my batch file.

rasdial "TATA PHOTON+" internet

@echo off
if ERRORLEVEL == 0 (echo MSGBOX "Connection successfully established to TATA PHOTON+" > %temp%\TEMPmessage.vbs
call %temp%\TEMPmessage.vbs
del %temp%\TEMPmessage.vbs /f /q)
else if ERRORLEVEL == 1 (echo MSGBOX "ERROR: Unable to establish connection" > %temp%\TEMPmessage.vbs
call %temp%\TEMPmessage.vbs
del %temp%\TEMPmessage.vbs /f /q
)

Answer 1

Try something like that :

rasdial "TATA PHOTON+" internet
@echo off
IF %ERRORLEVEL% EQU 0 (
    Goto :sucess
) else (
    GoTo :Fail
)
::****************************************************************************************
:sucess
(echo MSGBOX "Connection successfully established to TATA PHOTON+",VbInformation,"Connection successfully established to TATA PHOTON+" > %temp%\TEMPmessage.vbs
call %temp%\TEMPmessage.vbs
del %temp%\TEMPmessage.vbs /f /q
)
Exit /b
::****************************************************************************************
:Fail
(echo MSGBOX "ERROR: Unable to establish connection",vbCritical,"ERROR: Unable to establish connection" > %temp%\TEMPmessage.vbs
call %temp%\TEMPmessage.vbs
del %temp%\TEMPmessage.vbs /f /q
)
Exit /b
::****************************************************************************************

Answer 2

The line

if errorlevel == 0 do-something

is not valid syntax. Based on some quick tests, it would appear that the command processor is reinterpreting it as

if errorlevel 0 do-something

which means "if errorlevel is at least 0 do something".

Instead, I recommend

if %ERRORLEVEL% EQU 0 do-something

Using the percent-signs version allows you to test for equality and also correctly handles the case where the return value is negative.