---
name: "IPC::SharedMem"
section: "3p"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/IPC::SharedMem"
---

# IPC::SharedMem(3p)

SysV Shared Memory IPC object class

## NAME

IPC::SharedMem - SysV Shared Memory IPC object class

## SYNOPSIS

```
    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.

- 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.

- 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.

  ```
      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 and memwrite instead of shmread and shmwrite for accessing the shared memory segment. Returns true if successful, or false on error. See [**shmat**(2)](/shmat/2.md).

- detach

  Detach from the shared memory segment that previously has been attached to. Returns true if successful, or false on error. See [**shmdt**(2)](/shmdt/2.md).

- 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, Class::Struct

## 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.