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Perl 5 version 12.4 documentation
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IPC::SharedMem - SysV Shared Memory IPC object class


  2. use IPC::SharedMem;
  3. $shm = IPC::SharedMem->new(IPC_PRIVATE, 8, S_IRWXU);
  4. $shm->write(pack("S", 4711), 2, 2);
  5. $data = $shm->read(0, 2);
  6. $ds = $shm->stat;
  7. $shm->remove;


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


  • new ( KEY , SIZE , FLAGS )

    Creates a new shared memory segment 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.

    1. uid
    2. gid
    3. cuid
    4. cgid
    5. mode
    6. segsz
    7. lpid
    8. cpid
    9. nattach
    10. atime
    11. dtime
    12. 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.

  • detach

    Detach from the shared memory segment that previously has been attached to. Returns true if successful, or false on error. See 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.


IPC::SysV, Class::Struct


Marcus Holland-Moritz <>


Version 2.x, Copyright (C) 2007, 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.