Sorry, but it looks to me like the first reply above got it right. The OP said that if the value of $input was "hello there0", and the regex did not have a backslash in front of the "$" in the character class, the regex would match and yield "not okay" as the output. But this goes against the intent of the regex, which is to match only on the particular set of non-alphanumeric characters -- including "$" and "%".

The OP figured out that putting backslash in front of "$" would make the regex work as intended, but did not understand why, and everybody gave the correct explanation: without the backslash, you get an interpolation of the variable "$%", and its value turns out to be zero. Try this (NB: this uses bash shell style quoting): 

perl -le '$regex = qr:[<>@#$%^&*()_+=|\{\}\[\]\/\\]:;
print "$%";
print "$regex";'

[download]
You'll see a zero in both lines of output.

In reply to Re^3: Regex help by graff
in thread Regex help 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.