[Chapter 3] 3.2.136 semctl
Author: Larry Wall, Tom Christiansen & Randal L. Schwartz
Date: 1999-07-02T01:53:48Z

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| Chapter 3 Functions |

### 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.

3.2.135 select (ready file descriptors) |  | 3.2.137 semget