socket ?options? host port
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
The following options may also be present before host to specify additional information about the connection:
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.
Port specifies an integer port number to use for the client's side of the connection. If this option is omitted, the client's port number will be chosen at random by the system software.
-asyncoption 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 blocking 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.
The following additional option may also be specified before host:
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
The fconfigure command can be used to query several readonly configuration options for socket channels:
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.
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.
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 cannot be computed, the second element of the list is identical to the address, its first element.
Windows Server 2012. Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019.
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- flush, open, read
PTC MKS Toolkit 10.3 Documentation Build 39.