Net::LibResolv - a Perl wrapper around libresolv
Net::LibResolv
use Net::LibResolv qw( res_query NS_C_IN NS_T_A $h_errno ); use Net::DNS::Packet; my $answer = res_query( "www.cpan.org", NS_C_IN, NS_T_A ); defined $answer or die "DNS failure - $h_errno\n"; foreach my $rr ( Net::DNS::Packet->new( \$answer )->answer ) { print $rr->string, "\n"; }
The libresolv library provides functions to use the platform's standard DNS resolver to perform DNS queries. This Perl module provides a wrapping for the two primary functions, res_query(3) and res_search(3), allowing them to be used from Perl.
res_query(3)
res_search(3)
The return value from each function is a byte buffer containing the actual DNS response packet. This will need to be parsed somehow to obtain the useful information out of it; most likely by using Net::DNS.
Calls the res_query(3) function on the given domain name, class and type number. Returns the answer byte buffer on success, or undef on failure. On failure sets the value of the $h_errno package variable.
undef
$h_errno
$dname should be a plain string. $class and $type should be numerical codes. See the CONSTANTS section for convenient definitions.
$dname
$class
$type
CONSTANTS
Calls the res_search(3) function on the given domain name, class and type number. Returns the answer byte buffer on success, or undef on failure. On failure sets the value of the $h_errno package variable.
After an error from res_query or res_search, this variable will be set to the error value, as a dual-valued scalar. Its numerical value will be one of the error constants (see below); it string value will be an error message version of the same (similar to the $! perl core variable).
res_query
res_search
$!
if( !defined( my $answer = res_query( ... ) ) ) { print "Try again later...\n" if $h_errno == TRY_AGAIN; }
defined( my $answer = res_query( ... ) ) or die "Cannot res_query() - $h_errno\n";
The following set of constants define values for the $class parameter. Typically only NS_C_IN is actually used, for Internet.
NS_C_IN
NS_C_IN NS_C_CHAOS NS_C_HS NS_C_INVALD NS_C_NONE NS_C_ANY
Functions to convert between class names and ID values.
The following are examples of constants define values for the $type parameter. (They all follow the same naming pattern, named after the record type, so only a few are listed here.)
NS_T_A NS_T_NS NS_T_CNAME NS_T_PTR NS_T_MX NS_T_TXT NS_T_SRV NS_T_AAAA NS_T_INVALID NS_T_ANY
Functions to convert between type names and ID values.
The following constants define error values for $h_errno.
HOST_NOT_FOUND NO_ADDRESS NO_DATA NO_RECOVERY TRY_AGAIN
The values of NO_ADDRESS and NO_DATA may be the same.
NO_ADDRESS
NO_DATA
Net::DNS - Perl interface to the DNS resolver
Paul Evans <leonerd@leonerd.org.uk>
To install Net::LibResolv, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Net::LibResolv
CPAN shell
perl -MCPAN -e shell install Net::LibResolv
For more information on module installation, please visit the detailed CPAN module installation guide.