php - 尝试做 preg_match 以及匹配整个字符串长度

Question

有没有办法将 preg_match 与总字符串长度结合起来？我需要能够匹配字母数字，字符串内有单个下划线，总字符串长度<= n。

目前我正在使用的是：

preg_match('/^[A-Za-z0-9]*(?:_[A-Za-z0-9]+)*$/',$string) && (strlen($string) <= 10)

我已经玩这个太久了，试图将整个事情合并到 preg_match 中，所以只是添加了&& strlen，但我确信有更好的方法来做到这一点。

Answer 1

试一试：

preg_match('/^(?=[A-Za-z0-9]*(?:_[A-Za-z0-9]+)*).{1,10}$/', $string)

根据评论编辑：

/^(?=[A-Za-z0-9]+(?:_[A-Za-z0-9]+)*$).{5,25}$/

解释：

The regular expression:

(?-imsx:^(?=[A-Za-z0-9]+(?:_[A-Za-z0-9]+)*$).{5,25}$)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  (?=                      look ahead to see if there is:
----------------------------------------------------------------------
    [A-Za-z0-9]+             any character of: 'A' to 'Z', 'a' to
                             'z', '0' to '9' (1 or more times
                             (matching the most amount possible))
----------------------------------------------------------------------
    (?:                      group, but do not capture (0 or more
                             times (matching the most amount
                             possible)):
----------------------------------------------------------------------
      _                        '_'
----------------------------------------------------------------------
      [A-Za-z0-9]+             any character of: 'A' to 'Z', 'a' to
                               'z', '0' to '9' (1 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
    )*                       end of grouping
----------------------------------------------------------------------
    $                        before an optional \n, and the end of
                             the string
----------------------------------------------------------------------
  )                        end of look-ahead
----------------------------------------------------------------------
  .{5,25}                  any character except \n (between 5 and 25
                           times (matching the most amount possible))
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

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