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ActiveTcl User Guide
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dns(n) 1.0.4 "dns"
dns - Tcl Domain Name Service Client
package require Tcl 8.2
package require dns ?1.0.4?
The dns package provides a Tcl only Domain Name Service client.
You should refer to RFC 1034 (http://www.rfc-editor.org/rfc/rfc1034.txt)
and RFC 1035 (http://www.rfc-editor.org/rfc/rfc1035.txt)
for information about the DNS protocol or read resolver(3) to find
out how the C library resolves domain names. The intention of this
package is to insulate Tcl scripts from problems with using the
system library resolver for slow name servers. It may or may not be
of practical use. Internet name resolution is a complex business
and DNS is only one part of the resolver. You may find you are
supposed to be using hosts files, NIS or WINS to name a few other
systems. This package is not a substitute for the C library
resolver - it does however implement name resolution over DNS. The
package also extends the package uri to support
DNS URIs or the form dns:what.host.com or dns://my.nameserver/what.host.com.
The dns::resolve command can handle DNS URIs or
simple domain names as a query.
Note: The package defaults to using DNS over TCP
connections. If you wish to use UDP you will need to get the tcludp
package and get a version that correctly handles binary data. This
should be publicly available shortly.
- ::dns::resolve query ?options?
- Resolve a domain name using the DNS protocol. query is the domain name to be lookup up. This should be
either a fully qualified domain name or a DNS URI.
- -nameserver hostname or
-server hostname
- Specify an alternative name server for this request.
- -protocol tcp|udp
- Specify the network protocol to use for this request. Can be
one of tcp or udp.
- -port portnum
- Specify an alternative port.
- -search domainlist
- -timeout milliseconds
- Override the default timeout.
- -type TYPE
- Specify the type of DNS record you are interested in. Valid
values are A, NS, MD MF, CNAME, SOA, MB, MG, MR, NULL, WKS, PTR,
HINFO, MINFO, MX, TXT, AXFR, MAILB, MAILA and *. See RFC1035 for
details about the return values.
- -class CLASS
- Specify the class of domain name. This is usually IN but may be
one of IN for internet domain names, CS, CH, HS or * for any
class.
- -recurse boolean
- Set to false if you do not want the name
server to recursively act upon your request. Normally set to true.
- -command procname
- Set a procedure to be called upon request completion. The
procedure will be passed the token as its only argument.
- ::dns::configure ?options?
- The ::dns::configure command is used to setup the dns package.
The server to query, the protocol and domain search path are all
set via this command. If no arguments are provided then a list of
all the current settings is returned. If only one argument then it
must the the name of an option and the value for that option is
returned.
- -nameserver hostname
- Set the default name server to be used by all queries. The
default is localhost.
- -protocol tcp|udp
- Set the default network protocol to be used. Defaults to
tcp.
- -port portnum
- Set the default port to use on the name server. The default is
53.
- -search domainlist
- Set the domain search list. This is currently not used.
- -timeout milliseconds
- Set the default timeout value for DNS lookups. Defaults to 30
seconds.
- ::dns::name token
- Returns a list of all domain names returned as an answer to
your query.
- ::dns::address token
- Returns a list of the address records that match your
query.
- ::dns::cname token
- Returns a list of canonical names (usually just one) matching
your query.
- ::dns::status token
- Returns the status flag. For a successfully completed query
this will be ok. May be error or timeout
or eof. See also ::dns::error
- ::dns::error token
- Returns the error message provided for requests whose status is
error. If there is no error message then an empty string
is returned.
- ::dns::reset token
- Reset or cancel a DNS query.
- ::dns::wait token
- Wait for a DNS query to complete and return the status upon
completion.
- ::dns::cleanup token
- Remove all state variables associated with the request.
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% set tok [dns::resolve www.tcl.tk]
::dns::1
% dns::status $tok
ok
% dns::address $tok
199.175.6.239
% dns::name $tok
www.tcl.tk
% dns::cleanup $tok
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Using DNS URIs as queries:
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% set tok [dns::resolve "dns:tcl.tk;type=MX"]
% set tok [dns::resolve "dns://l.root-servers.net/www.tcl.tk"]
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Pat Thoyts
resolver(5)
DNS , domain name service , resolver , rfc 1034 , rfc 1035
Copyright © 2002, Pat Thoyts