IPC::SharedMem(3pm) Perl Programmers Reference Guide IPC::SharedMem(3pm)

# [NAME](#NAME)

IPC::SharedMem - SysV Shared Memory IPC object class

# [SYNOPSIS](#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](#DESCRIPTION)

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

# [METHODS](#METHODS)

[new ( KEY , SIZE , FLAGS )](#new)

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](#id)

Returns the shared memory identifier.

[read ( POS, SIZE )](#read)

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)

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)

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](#is_removed)

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

[stat](#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 ( \[FLAG\] )](#attach)

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)](/man/os/perl/shmat.2).

[detach](#detach)

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

[addr](#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](#SEE_ALSO)

IPC::SysV, Class::Struct

# [AUTHORS](#AUTHORS)

Marcus Holland-Moritz <mhx@cpan.org>

# [COPYRIGHT](#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.

2026-10-27 perl v5.44.0

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Document: IPC::SharedMem(3pm) from perl 5.44.0-r4 (Chainguard OS)
Source: https://github.com/Perl/perl5.git