I think the earlier replies have probably solved your problem, but I was curious about this statement:
However the IPaddress and Action part of each line may contain duplicates, its these duplicates I want to remove but still keep the output in time order.
Now, if "1.2.3.4 PowerOff" occurs today at 08:18 and again today at 10:20, do you want to keep the first record and delete the later one, or vice versa?

If you keep the first and delete later repeats, you just keep the IP/Action data as hash keys, and assuming the data are being read in chronological order, only output lines whose IP/Action are not yet in the hash.

In order to delete earlier occurrences and keep only the latest one, you have to store Date/Time as the value for each IP/Action key, and after you've read the whole input stream, sort the hash by its values in order to print each "hash_value hash_key" in chronological order.

In reply to Re: Removing duplicate entries in a file which has a time stamp on each line by graff
in thread Removing duplicate entries in a file which has a time stamp on each line by lambden

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.