If you can assume that urls will not contain (unencoded) spaces, then this might work for you: 

my $test = qq|
sdfiojs pfojsdfs fs [img]sdj fpsdofj spojf sfsf [b] [img]http://www.te
+st.com/image.gif[/img] dfs fs
s fsf sfd  [img]test.gif[/img]
|;

while ($test =~ /\[img\](\S+?)\[\/img\]/g) {
   print "$1 \n";
}

__END__
c:\test>junk
http://www.test.com/image.gif
test.gif

[download]

Alternatively, maybe this is better:

while ($test =~ /\[img\]([^\[\]]+?)\[\/img\]/g) {
   print "$1 \n";
}

[download]
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re: Possible with a regex? by BrowserUk
in thread Possible with a regex? by ultranerds

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.