如何使用 Java 在 CMD 中使用环境变量？

Question

我刚开始使用 ProcessBuilder 对象来执行 Java 中的运行命令。我的问题是，当我将环境变量放入 builder.command(...) 方法时，它不起作用。但是，当我对环境变量的字符串进行硬编码时，它可以完美运行。下面是我的代码以及有助于弄清楚我在做什么的解释：

ProcessBuilder builder = new ProcessBuilder();
    builder.directory(f);
    System.out.println("The user's chosen directory is: "+builder.directory());
    Map<String, String> environment = builder.environment();
    environment.put("WINDOW",w);
    environment.put("AUDIO",a);
    environment.forEach((key,value)->System.out.println("key is "+key+" "+"value: "+value));
    builder.command("ffmpeg", "-i", "$WINDOW","-i", "$AUDIO", "-vcodec", "copy" ,"output.mp4");

    Process pr= builder.start();

Explanation/Objective:

Basically I have a JButton in which an ActionListener is being fired off when the user clicks it. I am trying to use ffmpeg to convert an audio and video file together into one file if they desire. This code above will be executed in which I am trying to get the directory of the file they chose in my application to store the two files mentioned previously. Through using builder.directory(f), I am able to change the current directory of builder to that of the user's. I then created a map called environment in which I could add two environment variables called WINDOW and AUDIO. The two env. variables were assigned file names such that the file names were assigned to two variables w and a which are of type string. I did check to see if they were in the map and they were. I then attempt to make my set of instructions using the builder.command(...) method and then start the process using builder.start().

结论：

However, the singleoutput.mp4 file was not created and when I checked my Process using the waitFor() method I get a "1". On the contrary, when I don't use env. variables at all and hardcode the file names in between the parantheses where the env. variables were, it works correctly. So, exactly what am I doing wrong in my builder.command(..)? Thanks.

Answer 1

我觉得最简单的解决方案是：

builder.command("ffmpeg", "-i", w ,"-i", a, "-vcodec", "copy" ,"output.mp4");

如果您只打算使用它们来注入命令行参数，则无需设置环境变量。

但是，如果你确实想通过环境变量来完成，那么简单的方法就是使用一个subshell来完成所有的命令行解析和扩展；例如

builder.command("/bin/sh", "-c", 
                "ffmpeg -i $WINDOW -i $AUDIO -vcodec copy output.mp4");

您还可以使用引用、通配符、管道、重定向和所有其他奇特的 shell 功能。

如何使用 Java 在 CMD 中使用环境变量？

How to use environment variables in CMD using Java?

java

java-io