Reference: semget

semget

semget key, nsems, size, flags

Calls the System V IPC system call semget(2). The function returns the semaphore ID, or the undefined value 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.