DNS Lookup

jaldama has asked for the wisdom of the Perl Monks concerning the following question:

Howdy! I've spent some time reading about looking up a DNS in perl but am having trouble with my script. Hoping someone could give me a hint as to where I've gone wrong?

#!/usr/bin/perl-w
use Socket;


if ( $#ARGV != 0 ) {
print "Usage: $0 hostname\n";
exit(1);
}

$userinput = $ARGV[0];

if ($userinput =~ m/^(\d+)\.(\d+)\.(\d+)\.(\d+)$/ ) {
    $userinput = $ip;
    $hostname = gethostbyaddr(inet_aton($ip), AF_INET) or die "Can't R
+esolve $ip: $!\n";
    print $hostname;
}
else {
    $userinput = $name;
    $ipaddr = gethostbyname($name) or die "Can't resolve $name: $!\n";
    $ipaddr = inet_ntoa(inet_aton($name));
    print $ipaddr;
}


##prints this?
$ perl ddlookup.pl wbur.org
Can't resolve : No such file or directory
[download]

Comment on DNS Lookup Download Code

Replies are listed 'Best First'.
Re: DNS Lookup by toolic (Bishop) on Jan 19, 2012 at 19:34 UTC
Change: `$userinput = $name;` [download] to: `$name = $userinput;` [download] I think you were missing the warning that I see because your shebang line is messed up (add a space before the `-w`), and you are probably bypassing it anyway by invoking your script with the `perl` executable on the command line. Also add: `use warnings;` [download] use strict and warnings The same goes for `$userinput = $ip;`	[reply] [d/l] [select]
Re^2: DNS Lookup by JavaFan (Canon) on Jan 19, 2012 at 22:24 UTC
you are probably bypassing it anyway by invoking your script with the perl executable on the command line. Perl actually honors command line switches on the she bang line, even when invoked directly: `$ cat xxx #!/usr/bin/perl -w print undef; $ perl xxx Use of uninitialized value in print at xxx line 3.` [download]	[reply] [d/l]
Re^3: DNS Lookup by Anonymous Monk on Jan 20, 2012 at 03:44 UTC
Yes, for the most part :) `$ perl #!/usr/bin/perl -Mstrict -- Too late for "-Mstrict" option at - line 1.` [download]	[reply] [d/l]
Re^2: DNS Lookup by jaldama (Acolyte) on Jan 19, 2012 at 20:05 UTC
Ahh, life makes sense again.	[reply]
Re: DNS Lookup by Khen1950fx (Canon) on Jan 20, 2012 at 10:09 UTC
I'm familiar with the information that you have read. It was almost cool 10 years ago, but time marches on. As an experiment, here are two scripts: one uses Socket, and the second one uses Net::DNS. You'll find that Socket isn't satisfactory. Socket `#!/usr/bin/perl -l use strict; use warnings; use IO::Socket; use Socket qw(SOCK_STREAM getaddrinfo); my $hostname = 'www.perlmonks.org'; my ($err, @res) = getaddrinfo($hostname, "", {socktype => SOCK_STREAM}); die "Cannot getaddrinfo - $err" if $err; foreach my $ai (@res) { my ($err, $ipaddr) = getnameinfo($ai->{'addr'}, 'NI_NUMERICHOST', 'NIx_NOSERV'); die "Cannot getnameinfo - $err" if $err; print "$ipaddr"; }` [download] Net::DNS `#!/usr/bin/perl use strict; use warnings; use Net::DNS; my $host = 'www.perlmonks.org'; my $res = Net::DNS::Resolver->new; my $query = $res->search($host); if ($query) { foreach my $rr ($query->answer) { next unless $rr->type eq "A"; print $rr->address, "\n"; } } else { warn "Query failed: ", $res->errorstring; }` [download]	[reply] [d/l] [select]
Re^2: DNS Lookup by jaldama (Acolyte) on Jan 20, 2012 at 21:01 UTC
Socket did the trick for now but I did have Net::DNS in mind and will keep it there for more robust projects	[reply]