[^some_char]some_char 
##</code><code>##

 .*?some_char
##</code><code>##

use strict; 
use warnings; 
use 5.012;

my $string = <<END_OF_HTML;
<ul>
  <li>
    <div id="Show1400">
      <a href="../../../KeyboardKeys/RetainerClip/Acer/Aspire/1400">1400</a>
    </div>
  </li>
  <li>
    <div id="Show1410">
      <a href="../../../KeyboardKeys/RetainerClip/Acer/Aspire/1410">1410</a>
    </div>
  </li>
</ul>
END_OF_HTML

my $regex = qr{<a href=["']([^"']+)["']>[^<]+</a>};

while ($string =~ /$regex/g) {
    say $1;
}

--output:--
../../../KeyboardKeys/RetainerClip/Acer/Aspire/1400
../../../KeyboardKeys/RetainerClip/Acer/Aspire/1410