shmop_write() will write a string into shared memory block.
shmop_write() takes 3 parameters: shmid, which is the shared memory block identifier created by shmop_open(), data, a string that you want to write into shared memory block and offset, which specifies where to start writing data inside the shared memory segment.
This example will write data inside $my_string into shared memory block, $shm_bytes_written will contain the number of bytes written.