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 perlipc/"SysV IPC" and IPC::SysV
documentation.