As tachyon and atcroft pointed out, you can use LWP::Simple. However I have a situation where I have to send cookie along with the request. In that case, LWP::Simple does not help any more, and I use LWP::UserAgent:

use LWP::UserAgent;
use HTTP::Request;

use strict;
use warnings;

my $ua = LWP::UserAgent->new();
    my $request = HTTP::Request->new(GET => "http://blah.com/attachmen
+t.php?attachmentid=123");
    $request->header("Cookie", 'a=1; b=2; c=3');
    my $content = $ua->request($request)->content();
    open(FILE, ">", "foo.jpg");
    binmode(FILE);    
    print FILE $content;
    close FILE;
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