It should become pretty clear why the match fails if you add one diagnostic print to display both the search pattern and the string to be searched in.

use strict;
use warnings;

while(<DATA>)
{

my $comment_author1;
my $comment_author2;
my $interactions;

     if( $_ =~ /(.*?),(.*?),(.*?)$/gm) {
        $comment_author1 = $1;
        $comment_author2 = $2;
        $interactions = $3;


    print "DEBUG: Looking for '$comment_author2,$comment_author1' in $
+_\n";
    if( $_ =~ "$comment_author2,$comment_author1") {

    print "no match\n";
    }

    else { print "$comment_author1,$comment_author2,$interactions\n";

}
}
}


__DATA__

personA,personB,10
personB,personA,190
personA,personC,23
personA,personD,43
personE,personF,10

[download]

Do you see now where your logic has gone wrong? I think if you had used consistent indentation it might have been clear from the outset:

use strict;
use warnings;

while (<DATA>) {

    my $comment_author1;
    my $comment_author2;
    my $interactions;

    if ($_ =~ /(.*?),(.*?),(.*?)$/gm) {
        $comment_author1 = $1;
        $comment_author2 = $2;
        $interactions    = $3;
        
        print "DEBUG: Looking for '$comment_author2,$comment_author1' 
+in $_\n";
        if ($_ =~ "$comment_author2,$comment_author1") {
            print "no match\n";
        } else {
            print "$comment_author1,$comment_author2,$interactions\n";
        }
    }
}

__DATA__

personA,personB,10
personB,personA,190
personA,personC,23
personA,personD,43
personE,personF,10

[download]

In reply to Re: print lines which are not reverse duplicates by hippo
in thread print lines which are not reverse duplicates by Maire

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.