Perl 5 version 8.8 documentation



IO::Socket - Object interface to socket communications


  1. use IO::Socket;


IO::Socket provides an object interface to creating and using sockets. It is built upon the IO::Handle interface and inherits all the methods defined by IO::Handle.

IO::Socket only defines methods for those operations which are common to all types of socket. Operations which are specified to a socket in a particular domain have methods defined in sub classes of IO::Socket

IO::Socket will export all functions (and constants) defined by Socket.


  • new ( [ARGS] )

    Creates an IO::Socket , which is a reference to a newly created symbol (see the Symbol package). new optionally takes arguments, these arguments are in key-value pairs. new only looks for one key Domain which tells new which domain the socket will be in. All other arguments will be passed to the configuration method of the package for that domain, See below.


    As of VERSION 1.18 all IO::Socket objects have autoflush turned on by default. This was not the case with earlier releases.



See perlfunc for complete descriptions of each of the following supported IO::Socket methods, which are just front ends for the corresponding built-in functions:

  1. socket
  2. socketpair
  3. bind
  4. listen
  5. accept
  6. send
  7. recv
  8. peername (getpeername)
  9. sockname (getsockname)
  10. shutdown

Some methods take slightly different arguments to those defined in perlfunc in attempt to make the interface more flexible. These are

  • accept([PKG])

    perform the system call accept on the socket and return a new object. The new object will be created in the same class as the listen socket, unless PKG is specified. This object can be used to communicate with the client that was trying to connect.

    In a scalar context the new socket is returned, or undef upon failure. In a list context a two-element array is returned containing the new socket and the peer address; the list will be empty upon failure.

    The timeout in the [PKG] can be specified as zero to effect a "poll", but you shouldn't do that because a new IO::Select object will be created behind the scenes just to do the single poll. This is horrendously inefficient. Use rather true select() with a zero timeout on the handle, or non-blocking IO.

  • socketpair(DOMAIN, TYPE, PROTOCOL)

    Call socketpair and return a list of two sockets created, or an empty list on failure.

Additional methods that are provided are:

  • atmark

    True if the socket is currently positioned at the urgent data mark, false otherwise.

    1. use IO::Socket;
    2. my $sock = IO::Socket::INET->new('some_server');
    3. $sock->read($data, 1024) until $sock->atmark;

    Note: this is a reasonably new addition to the family of socket functions, so all systems may not support this yet. If it is unsupported by the system, an attempt to use this method will abort the program.

    The atmark() functionality is also exportable as sockatmark() function:

    1. use IO::Socket 'sockatmark';

    This allows for a more traditional use of sockatmark() as a procedural socket function. If your system does not support sockatmark(), the use declaration will fail at compile time.

  • connected

    If the socket is in a connected state the peer address is returned. If the socket is not in a connected state then undef will be returned.

  • protocol

    Returns the numerical number for the protocol being used on the socket, if known. If the protocol is unknown, as with an AF_UNIX socket, zero is returned.

  • sockdomain

    Returns the numerical number for the socket domain type. For example, for an AF_INET socket the value of &AF_INET will be returned.

  • sockopt(OPT [, VAL])

    Unified method to both set and get options in the SOL_SOCKET level. If called with one argument then getsockopt is called, otherwise setsockopt is called.

  • socktype

    Returns the numerical number for the socket type. For example, for a SOCK_STREAM socket the value of &SOCK_STREAM will be returned.

  • timeout([VAL])

    Set or get the timeout value associated with this socket. If called without any arguments then the current setting is returned. If called with an argument the current setting is changed and the previous value returned.


Socket, IO::Handle, IO::Socket::INET, IO::Socket::UNIX


Graham Barr. atmark() by Lincoln Stein. Currently maintained by the Perl Porters. Please report all bugs to <>.


Copyright (c) 1997-8 Graham Barr <>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

The atmark() implementation: Copyright 2001, Lincoln Stein <>. This module is distributed under the same terms as Perl itself. Feel free to use, modify and redistribute it as long as you retain the correct attribution.


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