3.2.136 semctl

semctl ID, SEMNUM, CMD, ARG

This function calls the System V IPC system call semctl(2). 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. The function returns like ioctl: the undefined value for error, "0 but true" for zero, or the actual return value otherwise. On error, it puts the error code into $!. Before calling, you should say:

require "ipc.ph";
require "sem.ph";

This function is available only on machines supporting System V IPC.