You're treating arbitrary text as a regex pattern, so it doesn't match what you expect it to match and it you get regex pattern compilation errors: 
Unmatched ( in regex; marked by <-- HERE in m/mozilla/5.0 ( <-- HERE m
+acintosh; u; safari/525/ at script.pl line 30.

[download]

I'm rather curious as to why you didn't mention that you were getting an error.

Perhaps you want 

# Does $user contain the string from $useragent
$user =~ /\Q$useragent\E/

[download]
or 
# Is $user equal to the string from $useragent
$user =~ /^\Q$useragent\E\z/

[download]
or 
# Is $user equal to the string from $useragent
$user eq $useragent

[download]

In reply to Re: unexpected loop behaviour when pattern matching by ikegami
in thread unexpected loop behaviour when pattern matching by jonnyfolk

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.