I am not quite sure about the requirements. If all that this needed is to put blanks for cols 1 and 2 when they are the same as the previous line, then..perhaps..??? 
#!/usr/bin/perl
use strict;
use warnings;

my $prev_line = <DATA>;
$prev_line =~ tr/:/ /;  # BTW, tr/// is really fast
print $prev_line;

while (my $this_line = <DATA>)
{
   $this_line =~ tr/:/ /;
   my ($prev_cols ,$prev_file_name) = $prev_line =~ /^\s*(.*?)(\S+)\s*
+$/;
   my ($this_cols, $this_file_name) = $this_line =~ /^\s*(.*?)(\S+)\s*
+$/;
  
   if ($prev_cols eq $this_cols)
   {
       $this_cols =~ s/\S/ /g;
   }
   print $this_cols, $this_file_name,"\n";
   $prev_line = $this_line;
}

=Prints
ULTRIX                      CW18.72.0.3          IP-HOST1.log
DEC_DECSTATION              CW180.72.0.3         IP_HOST_AL.log
DEC_DECSTATION_ADDR         CW180.72.0.3         IP_HOST_al2.log
FOR_VISITORS23_HOST         HL617.253.1101.2     IP_HOST_hostinfo.log
FOR_VISITORS24_HOST         HL617.253.1101.2     IP_HOST_hostinfo2.log
FOR_VISITORS25_HOST         HL617.253.1101.2     IP_HOST_webform3.log
                                                 IP_HOST_webform4.log
FOR_VISITORS25_HOST         HL617.253.1201.2     IP_HOST_webform4.log
=cut


__DATA__
ULTRIX              :       CW18.72.0.3          IP-HOST1.log
DEC_DECSTATION      :       CW180.72.0.3         IP_HOST_AL.log
DEC_DECSTATION_ADDR :       CW180.72.0.3         IP_HOST_al2.log
FOR_VISITORS23_HOST :       HL617.253.1101.2     IP_HOST_hostinfo.log
FOR_VISITORS24_HOST :       HL617.253.1101.2     IP_HOST_hostinfo2.log
FOR_VISITORS25_HOST :       HL617.253.1101.2     IP_HOST_webform3.log
FOR_VISITORS25_HOST :       HL617.253.1101.2     IP_HOST_webform4.log
FOR_VISITORS25_HOST :       HL617.253.1201.2     IP_HOST_webform4.log

[download]

In reply to Re^3: Storing the log file name as key/value in hash by Marshall
in thread Storing the log file name as key/value in hash by Magnolia25

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.