Here's what I've come up with so far (using some of the improvements suggested and benchmarking using GrandFather's example): 
my $hdr_search = qr{^\-{4}\s\d};

sub useIndex {
    my ($ip1, $ip2, $lines) = @_;

    for my $line (@$lines) {
        unless (($line =~ $hdr_search) || ($header)) {
            next;
        }
        unless ($line =~ $hdr_search) {
            print $line;  ## Print matching packet body
            next;
        }
        if (0 > index ($line, $ip1) || (0 > index ($line, $ip2))) {
            $header = 0;
            next;
        } else {
            print "\n$line"; ## Print matching packet header
            $header = 1;
        }
    }
}

[download]
Using the index function along with getting rid of IF cases early has definitely sped things up considerably. Thoughts?

In reply to Re: Parsing Large Text Files For Performance by bigbot
in thread Parsing Large Text Files For Performance by bigbot

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.