Linux: echo $$ returns wrong PID, why?

Question

linux

I'm making a daemon in php (the daemon starts in the screen), you need to find out the PID of the daemon directly inside the script.
On Linux, there is an echo $$ command that returns the PID of the current process.
I write in the daemon:

// Узнаем PID текущего процесса
        exec("echo $$", $pid);
        echo "PID Демона: $pid[0]\n";

I get the result:

But if you look at the processes through htop, then the process has a different PID:

At the same time, the number displayed by echo $$ is always 1 more than the PID of the process displayed in htop
You can, of course, simply decrease the displayed number by one and work with it, but I want to understand why this is happening.

Answer 1

echo $$ returns the pid of the shell that exec launched. The fact that the number is next to the desired one is a coincidence.
To get the pid of your own process in php, there is a corresponding function getmypid

Answer 2

Because exec runs it in a shell

Answer 3

enable htop mode t and see the children of the process ??

Answer 4

To execute "echo $$", exec starts bash, and hence $$ is the PID of the bash process.
You need:

$pid=getmypid();
echo "Process PID $pid"