regex - Php parse links/emails

Question

I am wondering if there is a simple snippet which converts links of any kind:

http://www.cnn.com to <a href="http://www.cnn.com">http://www.cnn.com</a>
cnn.com to <a href="http://www.cnn.com">cnn.com</a>
www.cnn.com to <a href="http://www.cnn.com">www.cnn.com</a>
abc@def.com to  to <a href="mailto:mailto:abc@def.com">mailto:abc@def.com</a>

I do not want to use any PHP5 specific library.

Thank you for your time.

UPDATE I have updated the above text to what i want to convert it to. Please note that the href tag and the text are different for case 2 and 3.

UPDATE2 Hows does gmail chat do it? Theirs is pretty smart and works only for real domains names. e.g. a.ly works but a.cb does not work.

Answer 1

yes , http://www.gidforums.com/t-1816.html

<?php
/**
   NAME        : autolink()
   VERSION     : 1.0
   AUTHOR      : J de Silva
   DESCRIPTION : returns VOID; handles converting
                 URLs into clickable links off a string.
   TYPE        : functions
   ======================================*/

function autolink( &$text, $target='_blank', $nofollow=true )
{
  // grab anything that looks like a URL...
  $urls  =  _autolink_find_URLS( $text );
  if( !empty($urls) ) // i.e. there were some URLS found in the text
  {
    array_walk( $urls, '_autolink_create_html_tags', array('target'=>$target, 'nofollow'=>$nofollow) );
    $text  =  strtr( $text, $urls );
  }
}

function _autolink_find_URLS( $text )
{
  // build the patterns
  $scheme         =       '(http://|https://)';
  $www            =       'www.';
  $ip             =       'd{1,3}.d{1,3}.d{1,3}.d{1,3}';
  $subdomain      =       '[-a-z0-9_]+.';
  $name           =       '[a-z][-a-z0-9]+.';
  $tld            =       '[a-z]+(.[a-z]{2,2})?';
  $the_rest       =       '/?[a-z0-9._/~#&=;%+?-]+[a-z0-9/#=?]{1,1}';            
  $pattern        =       "$scheme?(?(1)($ip|($subdomain)?$name$tld)|($www$name$tld))$the_rest";

  $pattern        =       '/'.$pattern.'/is';
  $c              =       preg_match_all( $pattern, $text, $m );
  unset( $text, $scheme, $www, $ip, $subdomain, $name, $tld, $the_rest, $pattern );
  if( $c )
  {
    return( array_flip($m[0]) );
  }
  return( array() );
}

function _autolink_create_html_tags( &$value, $key, $other=null )
{
  $target = $nofollow = null;
  if( is_array($other) )
  {
    $target      =  ( $other['target']   ? " target="$other[target]"" : null );
    // see: http://www.google.com/googleblog/2005/01/preventing-comment-spam.html
    $nofollow    =  ( $other['nofollow'] ? ' rel="nofollow"'            : null );     
  }
  $value = "<a href="$key"$target$nofollow>$key</a>";
} 

?>