semctl ID,SEMNUM,CMD,ARG
            Calls the System V IPC function semctl(2). You'll probably have
            to say

                use IPC::SysV;

            first to get the correct constant definitions. If CMD is
            IPC_STAT or GETALL, then ARG must be a variable that will hold
            the returned semid_ds structure or semaphore value array.
            Returns like "ioctl": the undefined value for error, ""0 but
            true"" for zero, or the actual return value otherwise. The ARG
            must consist of a vector of native short integers, which may be
            created with "pack("s!",(0)x$nsem)". See also "SysV IPC" in
            perlipc, "IPC::SysV", "IPC::Semaphore" documentation.

            Portability issues: "semctl" in perlport.