Here it is with some common tools. The concepts could be translated into Perl code. The grep takes out the blank lines, the uniq removes consecutive duplicates, and then sed adds an extra newline to the end of each line to put the blank lines back in again. Although in Perl it might be easier to make a blank line your input record separator, and then you'd just have to drop consecutive duplicates. 

grep -v ^$ fail.txt | uniq | sed 's/$/\n/'

[download]

Aaron B.
Available for small or large Perl jobs; see my home node.

In reply to Re: Delete Duplicate Entry in a text file by aaron_baugher
in thread Delete Duplicate Entry in a text file by astronogun

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.