Capturar URL do link

<?php

$_POST['url'] = "http://www.grandprix-tunis.gov.tn/fr/index.php?id=4";

if (isset($_POST['url'])) {
    $url = $_POST['url'];
    $f = @fopen($url,"r");
while($buf = fgets($f,1024)){
    $buf = fgets($f, 4096);
    preg_match_all("/<\s*a\s+[^>]*href\s*=\s*[\"']?([^\"' >]+)[\"' >]/isU",$buf,$words);
for( $i = 0; $words[$i]; $i++ ){
for( $j = 0; $words[$i][$j]; $j++ ){
    $cur_word = strtolower($words[$i][$j]);
    print "$cur_word<br></a>";
    }
  }
 }
}
?>