在正则表达式中使用冒号

Question

我是regex的新手.我在regularexperssion.com上研究它.问题是我需要知道正则表达式中冒号(:)的用法是什么..

例如 ..:

$pattern = '/^(([\w]+:)?\/\/)?(([\d\w]|%[a-fA-f\d]{2,2})+(:([\d\w]|%[a-fA-f\d]{2,2})+)?@)?([\d\w][-\d\w]{0,253}[\d\w]\.)+[\w]{2,4}(:[\d]+)?(\/([-+_~.\d\w]|%[a-fA-f\d]{2,2})*)*(\?(&?([-+_~.\d\w]|%[a-fA-f\d]{2,2})=?)*)?(#([-+_~.\d\w]|%[a-fA-f\d]{2,2})*)?$/';

哪个匹配

$url1  = "http://www.somewebsite.com";
$url2  = "https://www.somewebsite.com";
$url3  = "https://somewebsite.com";
$url4  = "www.somewebsite.com";
$url5  = "somewebsite.com";

是的任何帮助都会非常感激.. :)

Answer 1

结肠:只是结肠.它没有任何意义,除了特殊情况,例如,没有捕获的聚类(也称为非捕获组):

(?:pattern)

它也可以用在字符类中,例如:

[[:upper:]]

但是,在你的情况下,冒号只是一个冒号.

正则表达式中使用的特殊字符:

在角色类中[-+_~.\d\w]:

• - 手段 -
• + 手段 +
• _ 手段 _
• ~ 手段 ~
• . 手段 .
• \d 任何数字
• \w 意思是任何单词字符

这些符号具有此含义,因为它们用于符号类[].没有符号类+,.有特殊意义.

其他要素:

• =?意味着=可以发生0或1次; 换句话说=,可以发生与否,可选=.

Answer 2

我决定再给你一个并解释整个正则表达式:

^                 # anchor to start of line
(                 # start grouping
 (                # start grouping
  [\w]+           # at least one of 0-9a-zA-Z_
  :               # a literal colon
 )                # end grouping
 ?                # this grouping is optional
 \/\/             # two literal slashes
)                 # end capture
?                 # this grouping is optional
(
 (
  [\d\w]          # exactly one of 0-9a-zA-Z_
                  # having \d is redundant
  |               # alternation
  %               # literal % sign
  [a-fA-f\d]{2,2} # exactly 2 hexadecimal digits
                  # should probably be A-F
                  # using {2} would have sufficed
 )+               # at least one of this groups
 (                # start grouping
  :               # literal colon
  (
   [\d\w]
   |
   %
   [a-fA-f\d]{2,2}
  )+
 )?               # Same grouping, but it is optional
                  # and there can be only one
 @                # literal @ sign
)?                # this group is optional
(
 [\d\w]           # same as [\w], explained above
 [-\d\w]{0,253}   # includes a dash as a valid character
                  # between 0 and 253 of these characters
 [\d\w]           # end with \w.  They want at most 255
                  # total and - cannot be at the start
                  # or end
 \.               # literal period
)+                # at least one of these groups
[\w]{2,4}         # two to four \w characters
(
 :                # literal colon
 [\d]+            # at least one digit
)?
(
 \/               # literal slash
 (
  [-+_~.\d\w]    # one of these characters
  |              # *or*
  %              # % with two hex digit combo
  [a-fA-f\d]{2,2}
 )*              # zero or more of these groups
)*               # zero or more of these groups
(
 \?              # literal question mark
 (
  &?         # literal &amp or &
  (
   [-+_~.\d\w]
   |
   %
   [a-fA-f\d]{2,2}
  )
  =?             # optional literal =
 )*              # zero or more of this group
)?               # this group is optional
(
 #               # literal #
 (
  [-+_~.\d\w]
  |
  %
  [a-fA-f\d]{2,2}
 )*
)?
$                # anchor to end of line

了解元字符/序列是什么很重要.某些序列在某些上下文中使用时不是元(特别是字符类).我已经为你编目了:

meta没有上下文

• ^ - 零宽度起始线
• () - 分组/捕获
• ? - 零个或前一个序列之一
• + - 前述序列中的一个或多个
• * - 前面序列中的零个或多个
• [] - 角色类
• \w- 字母数字字符和_.的反面\W
• | - 交替
• {} - 长度断言
• $ - 零宽度行尾

这排除了:,@并且%在原始上下文中具有任何特殊/元含义.

meta里面的字符类

]结束角色类. -创建一系列字符,除非它位于字符类的开头或结尾.

分组断言

一个(?组合开始分组断言.例如,(?:表示组但不捕获.这意味着在正则表达式中/(?:a)/,它将匹配字符串"a",但a不会捕获用于替换或匹配组的字符串/(a)/.

?也可用于先行/向后断言与?=,?!,?<=,?<!. (?其次是任何序列,除了我在本节中提到的只是一个文字?.

Answer 3

:在您的情况下,冒号没有特殊用途:

(([\w]+:)?\/\/)?将匹配http://,https://,ftp://...

您可以找到冒号的一个特殊用途:开始时的每个捕获组(?:都不会出现在结果中.
例如,输入中使用"foobarbaz":

• /foo((bar)(baz))/ => { [1] => 'barbaz', [2] => 'bar', [3] => 'baz' }
• /foo(?:(bar)(baz))/ => { [1] => 'bar', [2] => 'baz' }