You seem to only run the if statement if nc completes successfully:

nc ... && if ...

This explains why 0 is never outputted. Since the if statement is not executed when nc fails, the else branch of the if statement is always unreachable.

Instead, use nc directly with if:

if nc -z 10.102.10.22 10003 >/dev/null; then
    echo 1
else
    echo 0
fi

You could probably also write this particular statement using short-circuit logic:

nc -z 10.102.10.22 10003 >/dev/null && echo 1 || echo 0

... but it's technically not the same thing as the if statement. This last command would execute echo 0 if either of nc or echo 1 failed.

The special variable $? is very rarely used. You only need it in situations where you need to use the exit status of some command later than one or more further commands have executed. For example, when returning an exit status from a shell function in some cases:

myfunction () {
    grep -q 'pattern' file
    err=$?

    if [ "$err" -ne 0 ]; then
        echo failed >&2
    fi

    return "$err"
}

Here, both the [ ... ] test and the echo resets $?.

You seem to only run the if statement if nc completes successfully:

nc ... && if ...

This explains why 0 is never outputted. Since the if statement is not executed when nc fails, the else branch of the if statement is always unreachable.

Instead, use nc directly with if:

if nc -z 10.102.10.22 10003 >/dev/null; then
    echo 1
else
    echo 0
fi

You could probably also write this particular statement using short-circuit logic:

nc -z 10.102.10.22 10003 >/dev/null && echo 1 || echo 0

... but it's technically not the same thing as the if statement. This last command would execute echo 0 if either of nc or echo 1 failed.

To get the nc command to exit after 10 seconds, use the GNU utility timeout:

if timeout 10 nc -z 10.102.10.22 10003 >/dev/null; then
    echo 1
else
    echo 0
fi

The special variable $? is very rarely used. You only need it in situations where you need to use the exit status of some command later than one or more further commands have executed. For example, when returning an exit status from a shell function in some cases:

myfunction () {
    grep -q 'pattern' file
    err=$?

    if [ "$err" -ne 0 ]; then
        echo failed >&2
    fi

    return "$err"
}

Here, both the [ ... ] test and the echo resets $?.

You seem to only run the if statement if nc completes:

nc ... && if ...

This explains why 0 is never outputted. Since the if statement is not executed when nc fails, the else branch of the if statement is always unreachable.

Instead, use nc directly with if:

if nc -z 10.102.10.22 10003 >/dev/null; then
    echo 1
else
    echo 0
fi

You could probably also write this particular statement using short-circuit logic:

nc -z 10.102.10.22 10003 >/dev/null && echo 1 || echo 0

... but it's technically not the same thing as the if statement. This last command would execute echo 0 if either of nc or echo 1 failed.

You seem to only run the if statement if nc completes successfully:

nc ... && if ...

This explains why 0 is never outputted. Since the if statement is not executed when nc fails, the else branch of the if statement is always unreachable.

Instead, use nc directly with if:

if nc -z 10.102.10.22 10003 >/dev/null; then
    echo 1
else
    echo 0
fi

You could probably also write this particular statement using short-circuit logic:

nc -z 10.102.10.22 10003 >/dev/null && echo 1 || echo 0

... but it's technically not the same thing as the if statement. This last command would execute echo 0 if either of nc or echo 1 failed.

The special variable $? is very rarely used. You only need it in situations where you need to use the exit status of some command later than one or more further commands have executed. For example, when returning an exit status from a shell function in some cases:

myfunction () {
    grep -q 'pattern' file
    err=$?

    if [ "$err" -ne 0 ]; then
        echo failed >&2
    fi

    return "$err"
}

Here, both the [ ... ] test and the echo resets $?.