Category: WWW scripts
Author/Contact Info Diego Zamboni
Description: Where I work, apache is configured not to resolve IP addresses into names for the access logs. To be able to properly process the access logs for my pages with a log-processing program (I use webalizer) I wrote the following script to resolve the IP addresses. Note that the local domain name needs to be changed for when the resolved name is local (machine name only, without domain). This happens sometimes when the abbreviated name is before the full name in /etc/hosts, for example.

Updated: as suggested by kudra, added a comment to the code about double-checking the name obtained, and why we don't do it in this case.

#!/usr/local/perl/bin/perl -w
# Resolve IP addresses in web logs.
# Diego Zamboni, Feb 7, 2000

use Socket;

# Local domain mame

while (<>) {
  if ($f[0] =~ /^[\d.]+$/) {
    if ($cache{$f[0]}) {
    else {
      if ($addr) {
        $name=gethostbyaddr($addr, AF_INET);
        if ($name) {
      # NOTE: To ensure the veracity of $name, we really
      # would need to do a gethostbyname on it and compare
      # the result with the original $f[0], to prevent
      # someone spoofing us with false DNS information.
      # See the comments below. For this application,
      # we don't care too much, so we don't do this.
          # Fix local names
          if ($name !~ /\./) {
    print join(" ", @f)."\n";
  else {
    print $_;