Java程序没有从终端获取输出 [英] Java program not getting output from terminal

问题描述

我正在从终端运行我的 Java 程序，我正在尝试使用我的代码中的 linux 命令来计算某个目录中的文件数量；我设法获得了除这个命令之外的所有其他命令的输出.

I am running my Java program from terminal and I am trying to count the number of files in a certain directory using a linux command in my code; I have managed to get output for all other commands but this one.

我的命令是:ls somePath/*.xml |wc -l

当我在我的代码中运行我的命令时，它似乎没有任何输出，但是当我在终端中运行完全相同的命令时，它工作得很好并且实际上输出了该目录中的 xml 文件数.

When I run my command in my code, it appears that it has nothing to output, yet when I run the same exact command in terminal it works just fine and actually outputs the number of xml files in that directory.

这是我的代码:

private String executeTerminalCommand(String command) {
    String s, lastOutput = "";
    Process p;
    try {
        p = Runtime.getRuntime().exec(command);
        BufferedReader br = new BufferedReader(
                new InputStreamReader(p.getInputStream()));
        System.out.println("Executing command: " + command);
        while ((s = br.readLine()) != null){//it appears that it never enters this loop since I never see anything outputted 
            System.out.println(s);
            lastOutput = s;
        }
        p.waitFor();
        p.destroy();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return lastOutput;//returns empty string ""
}

更新代码，带输出

private String executeTerminalCommand(String command) {
        String s, lastOutput = "";
        try {
            Process p = new ProcessBuilder().command("/bin/bash", "-c", command).inheritIO().start();           
            //Process p = Runtime.getRuntime().exec(command);
            BufferedReader br = new BufferedReader(
                    new InputStreamReader(p.getInputStream()));
            System.out.println("Executing command: " + command);
            while ((s = br.readLine()) != null){
                System.out.println("OUTPUT: " + s);
                lastOutput = s;
            }
            System.out.println("Done with command------------------------");
            p.waitFor();
            p.destroy();
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("LAST OUTPUT IS: " + lastOutput);
        return lastOutput;
    }

输出:

Executing command: find my/path -empty -type f | wc -l
Done with command------------------------
1
LAST OUTPUT IS:

推荐答案

要执行管道，您必须调用一个 shell，然后在该 shell 中运行您的命令.

To execute a pipeline, you have to invoke a shell, and then run your commands inside that shell.

Process p = new ProcessBuilder().command("bash", "-c", command).start();

bash 调用 shell 来执行您的命令，-c 表示从字符串中读取命令.因此，您不必将命令作为 ProcessBuilder 中的数组发送.

bash invokes a shell to execute your command and -c means commands are read from string. So, you don't have to send the command as an array in ProcessBuilder.

但是如果你想使用 Runtime 那么

But if you want to use Runtime then

String[] cmd = {"bash" , "-c" , command};
Process p = Runtime.getRuntime().exec(cmd);

注意:您可以在此处查看ProcessBuilder的优势和功能此处超过运行时

Note: You can check advantages of ProcessBuilder here and features here over Runtime

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