How to check if $? is not equal to zero in unix shell scripting?

Put it in a variable first and then try to test it, as shown below

ret=$?
if [ $ret -ne 0 ]; then
        echo "In If"
else
        echo "In Else"
fi

This should help.

Edit: If the above is not working as expected then, there is a possibility that you are not using $? at right place. It must be the very next line after the command of which you need to catch the return status. Even if there is any other single command in between the target and you catching it's return status, you'll be retrieving the returns_status of this intermediate command and not the one you are expecting.

You don't need to test if $? is not 0. The shell provides && and || so you can easily branch based on implicit result of that test:

some_command && {
    # executes this block of code,
    # if some_command would result in:  $? -eq 0
} || {
    # executes this block of code,
    # if some_command would result in:  $? -ne 0
}

You can remove either branch, depending on what you want. So if you just want to test for failure (i.e. $? -ne 0):

some_command_returning_nonzero || {
    # executes this block of code when:     $? -ne 0
    # and nothing if the command succeeds:  $? -eq 0
}

However, the code you provided in the question works, as is. I'm confused that you got syntax errors & concluded that $? was a string. It's most likely that the errant code causing the syntax error was not provided with the question. This is especially evident because you claim that no one else's solutions work either. When this happens, you have to re-evaluate your assumptions.

NB: The code above may give confusing results if the code inside the braces returns an error. In that case simply use the if command instead, like this:

if some_command; then
    # executes this block of code,
    # if some_command would result in:  $? -eq 0
else
    # executes this block of code,
    # if some_command would result in:  $? -ne 0
fi

Try this after execution of your script :

if [ $? -ne 0 ];
then
//statements//
fi