shmat

shmat($id, $addr, $flag) - attach the shared-memory segment $id and return an opaque address for it.

Pass undef as $addr to let the kernel choose where to attach; $flag takes SHM_RDONLY, SHM_RND and friends. The value that comes back is a string of raw address bytes, meaningful only to memread, memwrite and shmdt - do not print it or do arithmetic on it. Returns undef with $! set on failure; a negative $id sets $! to EINVAL without reaching the kernel.