如何使用java正则表达式来匹配一行 [英] How to use java regex to match a line

问题描述

原始数据是：

auser1 home1b
auser2 home2b
auser3 home3b

我想匹配一行，但使用 ^（。*？ ）$

I want to match a line, but it doesn't work using ^(.*?)$

但是，我可以使用 a（。*？）b 来匹配 user1 home1 。

However, I can use a(.*?)b to match user1 home1.

如何匹配 auser1 home1b

推荐答案

默认情况下， ^ 和 $ 分别匹配输入的开始和结束。您需要使用（？m）启用MULTI-LINE模式，这会导致 ^ 和 $ 匹配开头和结尾：

By default, ^ and $ match the start- and end-of-input respectively. You'll need to enable MULTI-LINE mode with (?m), which causes ^ and $ to match the start- and end-of-line:

(?m)^.*$

演示：

import java.util.regex.*;

public class Main {
    public static void main(String[] args) throws Exception {

        String text = "auser1 home1b\n" +
                "auser2 home2b\n" +
                "auser3 home3b";

        Matcher m = Pattern.compile("(?m)^.*$").matcher(text);

        while (m.find()) {
            System.out.println("line = " + m.group());
        }
    }
}

产生以下输出：

line = auser1 home1b
line = auser2 home2b
line = auser3 home3b

编辑我

^。* $ 与任何事情都不匹配的事实是因为。默认情况下与 \ r 和 \ n 。如果你用（？s）启用DOT-ALL，导致。也匹配那些，你会看到匹配的整个输入字符串：

EDIT I

The fact that ^.*$ didn't match anything is because the . by default doesn't match \r and \n. If you enable DOT-ALL with (?s), causing the . to match those as well, you'll see the entire input string being matched:

(?s)^.*$

编辑II

在这种情况下，你还要放弃 ^ 和 $ ，只需查找模式。* 。由于。与 \ n 不匹配，因此在寻找<$ c时，您将获得相同的匹配$ c>（？m）^。* $ ，正如@Kobi在评论中正确提到的那样。

EDIT II

In this case, you mind as well drop the ^ and $ and simply look for the pattern .*. Since . will not match \n, you'll end up with the same matches when looking for (?m)^.*$, as @Kobi rightfully mentioned in the comments.

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