Calls the System V IPC function msgctl(2). 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 that will hold the returned msqid_ds
structure.  Returns like ioctl:
the undefined value for error, "0 but true"
 for zero, or the actual
return value otherwise.  See also SysV IPC in perlipc and the
documentation for IPC::SysV  and
IPC::Semaphore .
Portability issues: msgctl in perlport.