Perl5 リファレンス

       shmctl ID,CMD,ARG
               Calls the System V IPC function shmctl.  You'll
               probably have to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If
               CMD is `IPC_STAT', then ARG must be a variable
               which will hold the returned `shmid_ds' structure.
               Returns like ioctl: the undefined value for error,
               "`0' but true" for zero, or the actual return
               value otherwise.  See also `IPC::SysV'