gethostbyaddr() - Network Utility Functions

Perl Tutorials - Herong's Tutorial Examples

Dr. Herong Yang, Version 5.10

Perl Tutorials - Herong's Tutorial Examples

∟gethostbyaddr() - Network Utility Functions

This section provides a tutorial example on how to use network utility functions to get default port numbers of standard network services, or get the host name on the network by a given IP address.

getprotobyname($protoName) - Returns the protocol number of the specified protocol name in scalar context, and ($protoName,$aliases,$protoNumber) in list context.

getservbyname($serviceName,$protoName) - Returns the port number of the specified network service name and protocol name in scalar context, and ($serviceName,$aliases,$portNumber,$protoName) in list context.

getservbyport($portNumber,$protoName) - Returns the network service name of the specified port number and protocol name in scalar context, and ($serviceName,$aliases,$portNumber,$protoName) in list context.

gethostbyname($hostName) - Returns the packed IP address of the specified host name in scalar context, and ($name,$aliases,$addrtype,$length,@addrs) in list context. The host name can also be specified in IP address format.

gethostbyaddr($packedHostAddress) - Returns the host name of the specified packed IP address in scalar context, and ($name,$aliases,$addrtype,$length,@addrs) in list context.

Here is sample program to show you how these functions work:

#- NetworkInfo.pm
#- Copyright (c) 1999 by Dr. Herong Yang, http://www.herongyang.com/
#
   $s = getprotobyname('tcp');
   @l = getprotobyname('tcp');
   print "\ngetprotobyname():\n";
   print "   scalar = ", $s, "\n";
   print "   list = (", join(',',@l), ")\n";
   $s = getservbyname('ftp', 'tcp');
   @l = getservbyname('ftp', 'tcp');
   print "\ngetservbyname():\n";
   print "   scalar = ", $s, "\n";
   print "   list = (", join(',',@l), ")\n";
   $s = getservbyport(23, 'tcp');
   @l = getservbyport(23, 'tcp');
   print "\ngetservbyport():\n";
   print "   scalar = ", $s, "\n";
   print "   list = (", join(',',@l), ")\n";
   $s = gethostbyname('www.perl.org');
   @l = gethostbyname('www.perl.org');
   print "\ngetservbyname():\n";
   print "   scalar = ", $s, "\n";
   print "   list = (", join(',',@l), ")\n";
   $s = gethostbyname('216.109.118.67');
   @l = gethostbyname('216.109.118.67');
   print "\ngetservbyname():\n";
   print "   scalar = ", $s, "\n";
   print "   list = (", join(',',@l), ")\n";
   $domain = 2;
   $s = gethostbyaddr(pack('C4', 216,109,118,67), $domain);
   @l = gethostbyaddr(pack('C4', 216,109,118,67), $domain);
   print "\ngethostbyaddr():\n";
   print "   scalar = ", $s, "\n";
   print "   list = (", join(',',@l), ")\n";
   exit;

Output:

getprotobyname():
   scalar = 6
   list = (tcp,TCP,6)

getservbyname():
   scalar = 21
   list = (ftp,,21,tcp)

getservbyport():
   scalar = telnet
   list = (telnet,,23,tcp)

getservbyname():
   scalar = ?v  
   list = (x2.develooper.com,www.perl.org,2,4,?v  )

getservbyname():
   scalar = +mvC
   list = (216.109.118.67,,2,4,+mvC)

gethostbyaddr():
   scalar = p4.www.dcn.yahoo.com
   list = (p4.www.dcn.yahoo.com,,2,4,+mvC)

Table of Contents

About This Book

Perl on Linux Systems

ActivePerl on Windows Systems

Data Types: Values and Variables

Expressions, Operations and Simple Statements

User Defined Subroutines

Perl Built-in Debugger

Name Spaces and Perl Module Files

Symbolic (or Soft) References

Hard References - Addresses of Memory Objects

Objects (or References) and Classes (or Packages)