电子邮件验证和用户名验证只接受字母、数字、下划线和DOT

你可以做：

if (!preg_match('/^(?!.*?'.'.)['w.]+@(?:[a-zA-Z0-9-]+'.)+[a-zA-Z]+$/', $email)) 
    return("Invalid email address"); 

为了防止2个连续点（.），使用负前瞻(?!.*?'.'.)

if (!preg_match('/^(?!.*?'.'.)[a-z0-9_.]+@[a-z0-9.-]+'.[a-z]+$/im', $email))
    return("Invalid email address"); 

解释：

^             # Assert position at the beginning of a line (at beginning of the string or after a line break character) (line feed)
(?!           # Assert that it is impossible to match the regex below starting at this position (negative lookahead)
   .             # Match any single character that is NOT a line break character (line feed)
      *?            # Between zero and unlimited times, as few times as possible, expanding as needed (lazy)
   '.            # Match the character “.” literally
   '.            # Match the character “.” literally
)
[a-z0-9_.]    # Match a single character present in the list below
                 # A character in the range between “a” and “z” (case insensitive)
                 # A character in the range between “0” and “9”
                 # A single character from the list “_.”
   +             # Between one and unlimited times, as many times as possible, giving back as needed (greedy)
@             # Match the character “@” literally
[A-Z0-9.-]    # Match a single character present in the list below
                 # A character in the range between “A” and “Z” (case insensitive)
                 # A character in the range between “0” and “9”
                 # The literal character “.”
                 # The literal character “-”
   +             # Between one and unlimited times, as many times as possible, giving back as needed (greedy)
'.            # Match the character “.” literally
[A-Z]         # Match a single character in the range between “A” and “Z” (case insensitive)
   +             # Between one and unlimited times, as many times as possible, giving back as needed (greedy)
'$             # Assert position at the end of a line (at the end of the string or before a line break character) (line feed)

您可以使用以下正则表达式来防止用户名中出现2个连续点：

^(?!.*'.'..*@)[a-zA-Z0-9_.]+@'S+'.[a-zA-Z]+$

请参阅此处的演示。

详细信息

• ^-字符串的开头
• (?!.*'.'..*@)-如果用户名部分只有两个连续的点，则会导致匹配失败
• [a-zA-Z0-9_.]+-一个或多个ASCII字母、数字或_或.
• @-一个@
• 'S+-1+非空白字符
• '.-一个点
• [a-zA-Z]+-1个或多个ASCII字母
• $—字符串结束

示例代码：

$re = "/^(?!.*''.''..*@)[a-zA-Z0-9_.]+@''S+''.[a-zA-Z]+$/m"; 
$str = "334345jtjert..j547j@ds.com'n334345jtjert.j547j@ds.com'nss-ee@sd.com'nfsd!@asd.com'n11-ee@sd.com"; 
preg_match($re, $str, $matches);

您可以使用这个：

[''w''-''+''&''*]+(?:''.[''w''-''_''+''&''*]+)*@(?:[''w-]+''.)+[a-zA-Z]{2,7}