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socket(n)			      Tcl Built-In Commands				socket(n)

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NAME
       socket - Open a TCP network connection

SYNOPSIS
       socket ?options? host port

       socket -server command ?options? port
_________________________________________________________________

DESCRIPTION
       This  command  opens a network socket and returns a channel identifier that may be used in
       future invocations of commands like read, puts and flush.  At present only the TCP network
       protocol is supported;  future releases may include support for additional protocols.  The
       socket command may be used to open either the client  or  server  side  of  a  connection,
       depending on whether the -server switch is specified.

CLIENT SOCKETS
       If the -server option is not specified, then the client side of a connection is opened and
       the command returns a channel identifier that can be used for both  reading  and  writing.
       Port  and host specify a port to connect to;  there must be a server accepting connections
       on this port.  Port is an integer port number and host is either a domain-style name  such
       as www.sunlabs.com or a numerical IP address such as 127.0.0.1.	Use localhost to refer to
       the host on which the command is invoked.

       The following options may also be present before host to  specify  additional  information
       about the connection:

       -myaddr addr
	      Addr gives the domain-style name or numerical IP address of the client-side network
	      interface to use for the connection.  This option  may  be  useful  if  the  client
	      machine has multiple network interfaces.	If the option is omitted then the client-
	      side interface will be chosen by the system software.

       -myport port
	      Port specifies an integer port number to use for the client's side of  the  connec-
	      tion.  If this option is omitted, the client's port number will be chosen at random
	      by the system software.

       -async The -async option will cause the client socket to be connected asynchronously. This
	      means  that  the socket will be created immediately but may not yet be connected to
	      the server, when the call to socket returns. When a gets or flush is  done  on  the
	      socket  before the connection attempt succeeds or fails, if the socket is in block-
	      ing mode, the operation will wait until the connection is completed  or  fails.  If
	      the  socket is in nonblocking mode and a gets or flush is done on the socket before
	      the connection attempt succeeds or fails, the  operation	returns  immediately  and
	      fblocked on the socket returns 1.

SERVER SOCKETS
       If the -server option is specified then the new socket will be a server for the port given
       by port.  Tcl will automatically accept connections to the given port.  For  each  connec-
       tion  Tcl  will create a new channel that may be used to communicate with the client.  Tcl
       then invokes command with three additional arguments: the name of  the  new  channel,  the
       address, in network address notation, of the client's host, and the client's port number.

       The following additional option may also be specified before host:

       -myaddr addr
	      Addr gives the domain-style name or numerical IP address of the server-side network
	      interface to use for the connection.  This option  may  be  useful  if  the  server
	      machine  has multiple network interfaces.  If the option is omitted then the server
	      socket is bound to the special address INADDR_ANY so that it can accept connections
	      from any interface.

       Server channels cannot be used for input or output; their sole use is to accept new client
       connections. The channels created for each incoming client connection are opened for input
       and  output.  Closing  the server channel shuts down the server so that no new connections
       will be accepted;  however, existing connections will be unaffected.

       Server sockets depend on the Tcl event mechanism to find  out  when  new  connections  are
       opened.	 If  the  application  doesn't	enter the event loop, for example by invoking the
       vwait command or calling the C procedure  Tcl_DoOneEvent,  then	no  connections  will  be
       accepted.

CONFIGURATION OPTIONS
       The  fconfigure	command  can  be used to query several readonly configuration options for
       socket channels: 									  |

       -error											  |
	      This option gets the current error status of the given socket.  This is useful when |
	      you need to determine if an asynchronous connect operation succeeded.  If there was |
	      an error, the error message is returned.	If there was no error, an empty string is |
	      returned.

       -sockname
	      This  option  returns  a list of three elements, the address, the host name and the
	      port number for the socket. If the host name cannot be computed, the second element
	      is identical to the address, the first element of the list.

       -peername
	      This  option  is	not supported by server sockets. For client and accepted sockets,
	      this option returns a list of three elements; these are the address, the host  name
	      and  the port to which the peer socket is connected or bound. If the host name can-
	      not be computed, the second element of the list is identical to  the  address,  its
	      first element.

SEE ALSO
       flush(n), open(n), read(n)

KEYWORDS
       bind, channel, connection, domain name, host, network address, socket, tcp

Tcl					       8.0					socket(n)
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