If you are expecting that your output file should always have the same number of lines as your input file, then there is something wrong with this part of your second while loop: 
while (my $line = <MIC>){
    chomp $line;
    next if exists $preused{$line};
    $preused{$line} = 1;
    ...

[download]
If the input file happens to contain any duplicate lines, every non-initial occurrence of a duplicated string will be missing from the output.

Things are added to the "%preused" hash at another point within that loop as well (although I don't really understand how that other part is supposed to work).

You should be looking at the input file to figure out: (a) how many duplicate lines there are, and (b) how many lines might get eliminated due to the conditions that cause other things to be added to %preused.

In reply to Re: Perl overwriting some lines by graff
in thread Perl overwriting some lines by perlbrahmin

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.