semop

semop 
key
, 
opstring

Calls the System V IPC system call semop(2) to perform semaphore operations such as signaling and waiting. opstring must be a packed array of semop structures. You can make each semop structure by saying pack('s*', $semnum, $semop, $semflag) . The number of semaphore operations is implied by the length of opstring . The function returns true if successful, or false if there is an error. 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.