You need to quote the meta characters in the regex with \Q and \E. Otherwise you need to escape the meta-characters (such as [ and .) with backslash (\).

Here's an example: 
#!/usr/bin/perl -w
use strict;

my $grp = qr/\[\d+-\d+\]/;

for (<DATA>) {
    print if /\d+\.\d+\.$grp\.(\d+|$grp)/;
}


__DATA__
123.145.[146-149].2
135.168.[10-115].[0-125]
135.168.12.[0-125]

[download]


Update:
Sorry I misread the question. If you are after a single regex to do range checking, you can use the match time interpolation technique.
#!/usr/bin/perl -w
use strict;

my $grp = qr/^123\.145\.(\d+)\.(\d+)$(??{ $1 >= 146 && $1 <= 148 ? '' 
+: 1})/;

for (<DATA>) {
    print if /$grp/;
}


__DATA__
123.145.130.3
123.145.146.3
123.145.147.3
123.145.148.3
123.145.149.3

[download]

In reply to Re: IP Filtering RegEx needed by Roger
in thread IP Filtering RegEx needed 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.