<!-- GENERATED by docs/sphinx/bin/20-reference (p5) from reference/bundled/IPC/SharedMem.md. Do not edit. -->

```{index} single: IPC::SharedMem
```

# IPC::SharedMem

SysV Shared Memory IPC object class

## SYNOPSIS

```perl
use IPC::SysV qw(IPC_PRIVATE S_IRUSR S_IWUSR);
use IPC::SharedMem;

$shm = IPC::SharedMem->new(IPC_PRIVATE, 8, S_IRWXU);

$shm->write(pack("S", 4711), 2, 2);

$data = $shm->read(0, 2);

$ds = $shm->stat;

$shm->remove;
```

## DESCRIPTION

A class providing an object based interface to SysV IPC shared memory.

## METHODS

- new ( KEY , SIZE , FLAGS )

    Creates a new shared memory segment of `SIZE` bytes size associated
    with `KEY`. A new segment is created if

    - `KEY` is equal to `IPC_PRIVATE`
    - `KEY` does not already have a shared memory segment associated
    with it, and `_FLAGS_ & IPC_CREAT` is true.

    On creation of a new shared memory segment `FLAGS` is used to
    set the permissions.  Be careful not to set any flags that the
    Sys V IPC implementation does not allow: in some systems setting
    execute bits makes the operations fail.

- id

    Returns the shared memory identifier.

- read ( POS, SIZE )

    Read `SIZE` bytes from the shared memory segment at `POS`. Returns
    the string read, or `undef` if there was an error. The return value
    becomes tainted. See [shmread](https://metacpan.org/pod/shmread).

- write ( STRING, POS, SIZE )

    Write `SIZE` bytes to the shared memory segment at `POS`. Returns
    true if successful, or false if there is an error. See [shmwrite](https://metacpan.org/pod/shmwrite).

- remove

    Remove the shared memory segment from the system or mark it as
    removed as long as any processes are still attached to it.

- is\_removed

    Returns true if the shared memory segment has been removed or
    marked for removal.

- stat

    Returns an object of type `IPC::SharedMem::stat` which is a sub-class
    of `Class::Struct`. It provides the following fields. For a description
    of these fields see you system documentation.

    ```text
    uid
    gid
    cuid
    cgid
    mode
    segsz
    lpid
    cpid
    nattch
    atime
    dtime
    ctime
    ```

- attach ( \[FLAG\] )

    Permanently attach to the shared memory segment. When a `IPC::SharedMem`
    object is attached, it will use [memread](https://metacpan.org/pod/memread) and [memwrite](https://metacpan.org/pod/memwrite) instead of
    [shmread](https://metacpan.org/pod/shmread) and [shmwrite](https://metacpan.org/pod/shmwrite) for accessing the shared memory segment.
    Returns true if successful, or false on error. See [shmat(2)](http://man.he.net/man2/shmat).

- detach

    Detach from the shared memory segment that previously has been attached
    to. Returns true if successful, or false on error. See [shmdt(2)](http://man.he.net/man2/shmdt).

- addr

    Returns the address of the shared memory that has been attached to in a
    format suitable for use with `pack('P')`. Returns `undef` if the shared
    memory has not been attached.

## SEE ALSO

[IPC::SysV](SysV.md), [Class::Struct](../Class/Struct.md)

## AUTHORS

Marcus Holland-Moritz <mhx@cpan.org>

## COPYRIGHT

Version 2.x, Copyright (C) 2007-2013, Marcus Holland-Moritz.

Version 1.x, Copyright (c) 1997, Graham Barr.

This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.