网址正则表达式展开

Question

我正在试图找出我在PHP中使用的这个正则表达式，但我是一个非常好的，所以对我来说非常困难。你能解释一下这个正则表达式做了什么吗？

/(?:https?:\/\/)?(?:[a-zA-Z0-9.-]+?\.(?:[a-zA-Z])|\d+\.\d+\.\d+\.\d+)/

非常感谢！

Answer 1

Brackets

[0-9] - It matches any decimal digit from 0 through 9.
[a-z] - It matches any character from lower-case a through lowercase z.
[A-Z] - It matches any character from uppercase A through uppercase Z.
[a-Z] - It matches any character from lowercase a through uppercase Z.

Quantifiers

p+ - It matches any string containing at least one p. 
p* - It matches any string containing zero or more p's.     
p? - It matches any string containing zero or one p's.  
p{N} - It matches any string containing a sequence of N p's     
p{2,3} - It matches any string containing a sequence of two or three p's.   
p{2, } - It matches any string containing a sequence of at least two p's.
p$ - It matches any string with p at the end of it.
^p - It matches any string with p at the beginning of it.

Expression & Description

[[:alpha:]] - It matches any string containing alphabetic characters aA through zZ. 
[[:digit:]] - It matches any string containing numerical digits 0 through 9.
[[:alnum:]] - It matches any string containing alphanumeric characters aA through zZ and 0 through 9.   
[[:space:]] - It matches any string containing a space.

有关详细信息，请参阅：Regex