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semctl ID,SEMNUM,CMD,ARG

Calls the System V IPC function semctl(2). 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 that 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. The ARG must consist of a vector of native short integers, which may be created with pack("s!",(0)x$nsem). See also "SysV IPC" in perlipc and the documentation for IPC::SysV and IPC::Semaphore.

Portability issues: "semctl" in perlport.