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
then ARG must be a variable that will hold the returned
structure. Returns like ioctl: undef for error; "
but true" for zero; and the actual return value otherwise.
See also SysV IPC in perlipc and the documentation for
Portability issues: shmctl in perlport.