[英]How does this Powershell Regex work?
'<Relation From="701047080" ObjectNumber="166543300" Output="77" To="464616324">' -match '(?<=Output=")[^"]*'
$matchs
then contains 77? $matchs
然后包含77?
Which is what I want, I just don't understand why it works? 这就是我想要的,我只是不明白为什么它有效?
I've found stuff saying I could: 我找到的东西说我可以:
match '(?<NAME>Some regex)'
But I have no Idea what '(?<=' does? And I would REALLY like to understand the syntax... 但我不知道'(?<='是什么?我真的很想理解语法......
I actually need to pull out the value of Output and To both... And only have powershell on the system I need to do this on... 我实际上需要提取Output和To两者的值...并且只需要在系统上使用powershell我需要这样做......
The expression (?<=Output=")
is a lookbehind . It matches only immediately after the string Output="
. 表达式
(?<=Output=")
是一个lookbehind 。它只在字符串Output="
之后立即匹配。
The expression [^"]*
is a negated character class . It matches all characters until the next double-quote (or to the end of the string if there are no more double-quotes). 表达式
[^"]*
是一个否定的字符类 。它匹配所有字符,直到下一个双引号(如果没有双引号,则匹配字符串的结尾)。
The [^"]*
says any number of characters other than "
. [^"]*
表示除"
之外的任何数量的字符。
The [^"]*
is the main expression. [^"]*
是主要表达方式。
The (?<=Output=")
is a lookbehind and makes sure that the main expression is following the expression in the lookbehind, in this case Output="
. (?<=Output=")
是一个lookbehind,并确保主表达式跟随lookbehind中的表达式,在这种情况下Output="
。 The lookbehind expression is not included in the match lookbehind表达式不包含在匹配中
I don't think the regex is optimal. 我不认为正则表达式是最优的。
You could have used: 你可以使用:
'<Relation From="701047080" ObjectNumber="166543300" Output="77" To="464616324">' -match 'Output="(.*?)"'
(with the regex being as simple as Output="(.*?)"
) (正则表达式与
Output="(.*?)"
一样简单)
and got the 77 in $matches[1]
在
$matches[1]
得到77分$matches[1]
The regex was probably just complicated with the lookbehind to make the Output="
be not part of the match. It makes the regex more complex and reduces performance. All you need is the above regex and extract 77 with the appropriate group. 正则表达式可能只是复杂的外观使得
Output="
不是匹配的一部分。它使正则表达式更复杂并降低性能。所有你需要的是上面的正则表达式并用适当的组提取77。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.