function linkify($text)
{
  $text = eregi_replace('(((f|ht){1}tp://)[-a-zA-Z0-9@:%_\+.~#?&//=]+)',
    '<a href="\\1">\\1</a>', $text);

  $text = eregi_replace('([[:space:]()[{}])(www.[-a-zA-Z0-9@:%_\+.~#?&//=]+)',
    '\\1<a href="http://\\2">\\2</a>', $text);

  $text = eregi_replace('([_\.0-9a-z-]+@([0-9a-z][0-9a-z-]+\.)+[a-z]{2,3})',
    '<a href="mailto:\\1">\\1</a>', $text);
  return $text;
}

Linkify - Convert Text to Links

regex

PHP