$line='<p><a href="test1.htm"> test1</a><br> <a href="test2.htm"> test2</a><br> <a href="test3.htm"> test3</a><br> <a href="test4.htm"> test4</a><br>';

while ( $line=~/<a href=\"(.*?)\.htm\">/ig ) {
    $tmp=$1;

    print "LINE: $line\n";
    print "TMP: $tmp KK\n\n";

    $line=~s/<a href=\"$tmp.htm\">/<a href=\"\/xxx.html\">/i;
}