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, 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.