#!/usr/bin/perl -w

while(<DATA>) {
    if (/permalink/) {
        s|<permalink>(.*)</permalink>|$1|i;
        print;
    }
}

__DATA__
<permalink> Link A </permalink>
<tempNode> value1 </tempNode>
SomeText
<permalink> Link B </permalink>
<tempNode2> value2 </tempNode2>
<permalink> Link C </permalink>

##</code><code>##

 Link A
 Link B
 Link C