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Calls the System V IPC function semctl(). You'll probably have to say

use IPC::SysV;

first to get the correct constant definitions. If CMD is IPC_STAT or GETALL, then ARG must be a variable which will hold the returned semid_ds structure or semaphore value array. Returns like ioctl(): the undefined value for error, "0 but true" for zero, or the actual return value otherwise. See also IPC::SysV and IPC::Semaphore documentation.