\z, as proposed by haukex might be the most appropriate solution: it only matches at the absolute end of the string, so both greedy and non greedy variants do what you want.

$p = substr($s, @-[1], (@+[1] - @-[1])); is a strange way to write $p = $1; you know you can access captures with $X with X the number of the of the capture right?

Also, rather than trying to make your output more explicit with enclosing [ and string length, I strongly advise you to use Data::Dump (or the Core Data::Dumper, but you have to set $Data::Dumper::useqq = 1; for the more explicit version) for debugging (it will take care or invisible, or look-alike characters for you, and works well with refs and structures) 

use Data::Dump 'pp';
$s = "abc\n";
if ($s =~ /(ab.*?)\z/s) {
    pp($1);
}
if ($s =~ /(ab.*)\z/s) {
    pp($1);
}

__END__
"abc\n"
"abc\n"

[download]

In reply to Re^3: Regex not matching closing newline? by Eily
in thread Regex not matching closing newline? by rverscho

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.