One minor difference is that splitting this way removes the close-paragraph, but not the open-paragraph, so you need to remove it. 
my @arr = grep {/\[tab\]/ and s/^<p>//} split /<\/p>/, $contents;

[download]
If you wanted to retain both tags, you could do so by splitting on a lookbehind expression: 
my @arr = grep /\[tab\]/, split /(?<=<\/p>)/, $contents;

[download]
You'd also retain the paragraph-close if you used it for $/ and read the string as a file. 
{
  local $/ = '</p>';
  open (STR, '<', \$contents) or die "Opening string: $!\n";
  @arr = grep /^<p>/ && /\[tab\]/, <STR>;
  print "read $_\n" for @arr;
}

[download]
But now I'm just getting silly.
Caution: Contents may have been coded under pressure.

In reply to Re^2: Matching set of paragraph tags with string inside. by Roy Johnson
in thread Matching set of paragraph tags with string inside. by the_0ne

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.