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Special Forums IP Networking gethostbyname_r returns NULL when hostname has dash Post 302197755 by uunniixx on Wednesday 21st of May 2008 03:24:42 PM
Old 05-21-2008
Below are my personal findings:


Example 1:

Code:
> host nyustern-.collegemailer.com
nyustern-.collegemailer.com has address 209.200.118.155

> host nyustern.collegemailer.com
nyustern.collegemailer.com has address 209.200.118.155

Example 2:

Code:
> nslookup nyustern-.collegemailer.com
Note:  nslookup is deprecated and may be removed from future releases.
Consider using the `dig' or `host' programs instead.  Run nslookup with
the `-sil[ent]' option to prevent this message from appearing.
Server:         xx.xxx.xx.xxx
Address:       xx.xxx.xx.xxx#xx
 
Non-authoritative answer:
Name:   nyustern-.collegemailer.com
Address: 209.200.118.155
 
> nslookup nyustern.collegemailer.com
Note:  nslookup is deprecated and may be removed from future releases.
Consider using the `dig' or `host' programs instead.  Run nslookup with
the `-sil[ent]' option to prevent this message from appearing.
Server:         xx.xxx.xx.xxx
Address:       xx.xxx.xx.xxx#xx
 
Non-authoritative answer:
Name:   nyustern.collegemailer.com
Address: 209.200.118.155

Example 3:

This code uses gethostbyname_r method to determine the address:-

Code:
> a.out nyuster-n.collegemailer.com
addresses:   209.200.118.155
> a.out ny-uster-n.collegemailer.com
addresses:   209.200.118.155
> a.out ny-uster-n-.collegemailer.com
unknown host `ny-uster-n-.collegemailer.com'
> a.out ny---uster-n.collegemailer.com
addresses:   209.200.118.155
> a.out nyustern.collegemailer.com
addresses:   209.200.118.155
>

I am unsure whether '-' in hostname ignored or does not has a functionality. In such a case having a trailing '-' is just a corner off case.

Last edited by uunniixx; 05-25-2008 at 06:16 PM..
 

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Net::Nslookup(3pm)					User Contributed Perl Documentation					Net::Nslookup(3pm)

NAME
Net::Nslookup - Provide nslookup(1)-like capabilities SYNOPSIS
use Net::Nslookup; my @addrs = nslookup $host; my @mx = nslookup(type => "MX", domain => "perl.org"); DESCRIPTION
"Net::Nslookup" provides the capabilities of the standard UNIX command line tool nslookup(1). "Net::DNS" is a wonderful and full featured module, but quite often, all you need is `nslookup $host`. This module provides that functionality. "Net::Nslookup" exports a single function, called "nslookup". "nslookup" can be used to retrieve A, PTR, CNAME, MX, NS, SOA, and TXT records. my $a = nslookup(host => "use.perl.org", type => "A"); my @mx = nslookup(domain => "perl.org", type => "MX"); my @ns = nslookup(domain => "perl.org", type => "NS"); my $name = nslookup(host => "206.33.105.41", type => "PTR"); "nslookup" takes a hash of options, one of which should be term, and performs a DNS lookup on that term. The type of lookup is determined by the type argument. If server is specified (it should be an IP address, or a reference to an array of IP addresses), that server(s) will be used for lookups. If only a single argument is passed in, the type defaults to A, that is, a normal A record lookup. If "nslookup" is called in a list context, and there is more than one address, an array is returned. If "nslookup" is called in a scalar context, and there is more than one address, "nslookup" returns the first address. If there is only one address returned, then, naturally, it will be the only one returned, regardless of the calling context. domain and host are synonyms for term, and can be used to make client code more readable. For example, use domain when getting NS records, and use host for A records; both do the same thing. server should be a single IP address or a reference to an array of IP addresses: my @a = nslookup(host => 'example.com', server => '4.2.2.1'); my @a = nslookup(host => 'example.com', server => [ '4.2.2.1', '128.103.1.1' ]) By default, when doing CNAME, MX, and NS lookups, "nslookup" returns names, not addresses. This is a change from versions prior to 2.0, which always tried to resolve names to addresses. Pass the recurse => 1 flag to "nslookup" to have it follow CNAME, MX, and NS lookups. Note that this usage of "recurse" is not consistent with the official DNS meaning of recurse. # returns soemthing like ("mail.example.com") my @mx = nslookup(domain => 'example.com', type => 'MX'); # returns soemthing like ("127.0.0.1") my @mx = nslookup(domain => 'example.com', type => 'MX', recurse => 1); SOA lookups return the SOA record in the same format as the `host` tool: print nslookup(domain => 'example.com', type => 'SOA'); dns1.icann.org. hostmaster.icann.org. 2011061433 7200 3600 1209600 3600 TIMEOUTS
Lookups timeout after 15 seconds by default, but this can be configured by passing timeout => X to "nslookup". DEBUGGING
Pass debug => 1 to "nslookup" to emit debugging messages to STDERR. AUTHOR
darren chamberlain <darren@cpan.org> perl v5.12.4 2011-08-15 Net::Nslookup(3pm)
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