正则表达式判断email和URL, 帮忙看看有没有要补充的._PHP教程

echo 'a:'.htmlspecialchars($a);
echo '
a1:';
$a1 = eregi_replace('(^[_.][:alnum:]-]+@([[:alnum:]][[:alnum:]-]*.)+[[:alpha:]]{2,3}$)',' 1 ', $a) ;
echo htmlspecialchars($a1);
echo "
a1:$a1";
echo '
a2:';
$a2 = eregi_replace('([[:alnum:]]+://([[:alnum:]][[:alnum:]-]*.)+[[:alpha:]]{2,3}([#?/][^#?/][:space:]][^[:space:]]*)?)',
        '1', $a);
echo htmlspecialchars($a2);
echo "
a2:$a2";
// eregi('^[_.][:alnum:]-]+@([[:alnum:]][[:alnum:]-]*.)+[[:alpha:]]{2,3}$',$a) or die("not a email");
?>