大括号中包含数字的正则表达式

Question

我得到了这个正则表达式:

^\+[0-9]{12,12}$

谁能解释一下大括号{12,12}之间的两个值的含义？

Answer 1

{12,12} 是一个量词(参见 Limiting Repetition section )，它告诉正则表达式引擎前面的子模式应该重复最少 12 次和最多 12 次。在 ^+[0-9]{12,12}$ 中表示 0-9 范围内的数字应恰好重复 12 次。字符串应以加号开头，且仅包含加号+12位数字。

The syntax is {min,max}, where min is zero or a positive integer number indicating the minimum number of matches, and max is an integer equal to or greater than min indicating the maximum number of matches. If the comma is present but max is omitted, the maximum number of matches is infinite. So {0,1} is the same as ?, {0,} is the same as *, and {1,} is the same as +. Omitting both the comma and max tells the engine to repeat the token exactly min times.

因此，我们可以使用{12}(它等于{12,12}):

^\+[0-9]{12}$

参见 demo at regex101.com