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.