When you're dealing with something in a known/spec'd format, it's usually best to reach for a parser.

use URI;
use URI::QueryParam;

while ( <DATA> )
{
    chomp;
    my $uri = URI->new($_);
    print $uri, "\n";
    for my $param ( qw( id username ) )
    {
        printf("   %s --> %s\n", $param,
               join(", ", $uri->query_param($param))
               );
    }
}

__DATA__
http://beta.websitename.com/tool/view/mb/file?id=3323213&username=anir
+udh007
http://beta.websitename.com/tool/view/mb/file?username=anirudh007&id=4
+3242342
[download]

See recent: url get variables regex