Maybe I'm not getting what you mean but I think you are not understanding pattern matching correctly.

Can someone tell me why it is matching the . or the - at the end of the line?
In both cases, the last character is not matched by the regex! 
if ($domain =~ /[A-Z0-9]+[A-Z0-9-]+[A-Z0-9]/i) {
  # do A
} else {
  # do B
}

[download]
does A or B depending on whether the pattern matched the string $domain or not. It does not change $domain in any way, however. And your pattern does not have to match the whole string: 
# /[A-Z0-9]+[A-Z0-9-]+[A-Z0-9]/i matches
someDomain
someDomain..
..someDomain..
_!@#!@#!@#01a!@#$
# and so on

[download]
If you are interested in what was matched, you have to use capturing parentheses like this: 
if ($domain =~ /([A-Z0-9]+[A-Z0-9-]+[A-Z0-9])/i) {
  # $1 contains what is in the first pair of parentheses
  print "$1 matched\n\n"; 
} else {
  print "$domain did not match\n\n";
}

[download]
Play around with this code and different pattern. Furthermore include the assertion ^ and $ into the pattern as mentioned by OeufMayo and play some more.

-- Hofmator

In reply to Re: Regular expression matching when it shouldn't by Hofmator
in thread Regular expression matching when it shouldn't by Anonymous Monk

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.