=over =item msgctl ID,CMD,ARG 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 C, then ARG must be a variable which will hold the returned C structure. Returns like C: the undefined value for error, C<"0 but true"> for zero, or the actual return value otherwise. See also L, C, and C documentation. =back