在Linux上执行grep命令并捕获结果

Question

我正在尝试使用以下Java代码在linux上执行grep命令，但无法捕获输出。 我总是在输出中为null

Process p;
        String output = null;
        try {
            String command = "grep searchString filename.txt";
            System.out.println("Running command: " + command);

            p = Runtime.getRuntime().exec(command);

            BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));

            if (null != output) {

                while ((output = br.readLine()) != null)
                    System.out.println(output);
            } 

            p.waitFor();
            System.out.println("exit: " + p.exitValue());
            p.destroy();
        } catch (Exception e) {
            e.printStackTrace();

    }

如何捕获输出？ 是否有任何第三方库或更好的方法在linux上执行命令并捕获输出？

Answer 1

如果进行检查，则未分配output 。 如下更改代码：

    Process p;
    String output = null;
    try {
        String command = "grep searchString filename.txt";
        System.out.println("Running command: " + command);

        p = Runtime.getRuntime().exec(command);
        p.waitFor();

        BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));

            while ((output = br.readLine()) != null) {
                System.out.println(output);
                // Process your output here
            }

        System.out.println("exit: " + p.exitValue());
        p.destroy();
    } catch (Exception e) {
        e.printStackTrace();

}