正则表达式问题

[Venne]

写一个正则表达式，匹配URL地址，诸如http://、ftp://或者纯粹www.之类的地址，并且不能匹配在HTML标签内的url地址，如下：

fwww.fdsjkfsd.com http://fdjlkfd.com.com.f ftp://fdjkfdsf./df
fdsalfkdsja fsdahflksda fasdjlkfdsa tht.fdjfkld.fdfjlds.fsdlfj fdjsakl
tjhl<img src="../fdjkfd/fdlfd.gif"> fdjksffdslkaj <a href="http://fdjkfd.fdkfd.fdlcom">

正则表达式可以匹配：
fwww.fdsjkfsd.com
http://fdjlkfd.com.com.f
ftp://fdjkfdsf./df
不能匹配<img >标签里的fdlfd.gif 和<a>标签里的http://fdjkfd.fdkfd.fdlcom

敬请高手解惑……

[xyzxyz1111]

#!/usr/bin/perl


$_ = 'fwww.fdsjkfsd.com http://fdjlkfd.com.com.f ftp://fdjkfdsf./df
fdsalfkdsja fsdahflksda fasdjlkfdsa tht.fdjfkld.fdfjlds.fsdlfj fdjsakl
tjhl<img src="../fdjkfd/fdlfd.gif"> fdjksffdslkaj <a href="http://fdjkfd.fdkfd.fdlcom">';

while(/(\<((\"[^\"]*\")|[^>]*?)\>)|(http\:\/\/[\w.\/]+|ftp\:\/\/[\w.\/]+|[\w.\/]*?www\.[\w.\/]+)/gi){
print "$4\n" if ($4);
}