CODEWITHSUNDEEP
javalinuxcommand-lineexec
Lei Yang
Lei Yang

Reputation: 4335

Java Runtime.exec fail with space in linux

I searched a lot but did not find the solution. My goal is using java to call commands and get output in windows and linux. I found Runtime.exec method and did some experiments. Everything went ok except when there's space in the command parameters. Test code as below, also in github.
The code works well on windows, but in linux, output is empty:

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
public static void main(String[] args) {
    try {
        Runtime rt = Runtime.getRuntime();
        String[] commandArray;
        if (isWindows()) {
            commandArray = new String[]{"cmd", "/c", "dir", "\"C:\\Program Files\""};
        } else {
            commandArray = new String[]{"ls", "\"/root/a directory with space\""};
        }
        String cmd = String.join(" ",commandArray);
        System.out.println(cmd);

        Process process = rt.exec(commandArray);
        BufferedReader input = new BufferedReader(
                new InputStreamReader(process.getInputStream()));
        String result = "";
        String line = null;
        while ((line = input.readLine()) != null) {
            result += line;
        }
        process.waitFor();
        System.out.println(result);

    } catch (Exception e) {
        System.out.println(e.getMessage());
    }
}

public static boolean isWindows() {
    String OS = System.getProperty("os.name").toLowerCase();
    return (OS.indexOf("win") >= 0);
    }
}

if I execute the printed command in bash directly, then the output is as expected.

[root@localhost javatest]# javac Main.java 
[root@localhost javatest]# java Main
ls "/root/a directory with space"

[root@localhost javatest]# ls "/root/a directory with space"
a.txt  b.txt
[root@localhost javatest]#

Can anyone explain why and give ways to solve?

Upvotes: 0

Views: 347

Answers (1)

Andreas
Andreas

Reputation: 159096

There are two versions of exec.

  • exec(String command)

    Here you specify a command in a similar way to how you would do it on the command-line, i.e. you need to quote arguments with spaces.

    cmd /c dir "C:\Program Files"

  • exec(String[] cmdarray)

    Here you specify the arguments separately, so the arguments are given as-is, i.e. without quotes. The exec method will take care of any spaces and quote-characters in the argument, correctly quoting and escaping the argument as needed to execute the command.

    cmd
/c
dir
C:\Program Files

So, remove the extra quotes you added:

if (isWindows()) {
    commandArray = new String[] { "cmd", "/c", "dir", "C:\\Program Files"};
} else {
    commandArray = new String[] { "ls", "/root/a directory with space"};
}

Upvotes: 2

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