I would reccomend using Tie::File for this.
Frankly, rewriting the whole file to change just a few lines is a problematic situation with flat files. Although I would prefer some sort of database backend, Tie::File gives a database, without any necessary fields, etc.

You can read about Tie::File (Writen by Dominus) here, or go to cpan and download the module. Here's an example of how to edit a file from his article. 
        tie @lines, 'Tie::File', 'file' or die ...;
        for (@lines) {
          # Do your thing, only for lines that match this regex, or ar
+e records that need to be changed.
        }
        untie @lines;

[download]
It should be quicker.
Gyan Kapur
gyan.kapur@rhhllp.com

In reply to Re: Tie::File by Revelation
in thread Performance Question by Jarinn

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.