semctl

semctl 
id
, 
semnum
, 
cmd
, 
arg

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.