preg_replace-如果$4为空,则不包括字符串

我不确定这个花哨的瑞格舞真的是必要的
但是让我们看看……

啊,我把这个地区修改了大约4美元
允许缺少分机号码。你能认出吗 区别?

...
$regex_phone = 
  '/^
     (?:
       1(?:[. -])?
     )?
     (?: 
       \( (?=\d{3} \) ) # possible mistake? (probably correct)
     )?
     ([2-9]\d{2})       # $1
     (?:
       (?<=\(\d{3})\)
     )?
     \s?
     (?:
       (?<=\d{3})
       [.-]
     )?
     ([2-9]\d{2})       # $2
     [.\s-]?
     (\d{4})            # $3
     (?:
       \s? ext [.\s]? 
       (\d{1,5})?       # $4
     )?
 $/ix';

if( preg_match( $regex_phone, $data['phone'], $m) ) { 
   $data['phone'] = "$m[1] $m[2]-$m[3]" . (isset($m[4]) ? " ext.$m[4]" : '');
}
else { 
   $error[] = "Please enter a valid phone number.<br />"; 
}
...

当做

RBO