shell - How can I run Linux commands on an Android device?

Question

On some Android devices, in the ADB shell, I can only run echo, cd, ls. When I run:

tar -cvf //mnt/sdcard/BackUp1669/apk/test.tar /mnt/sdcard/test.apk

Or the command cp, it returns:

sh: tar: not found

Why can I not run these commands? Some devices support these commands. My end goal is to copy a file from the /data/data folder to SD card. I got su and I got the following code:

int timeout = 1000;
String command = "tar -cvf /" + Environment.getExternalStorageDirectory() + "/cp/"
        + packageName + ".tar" + " " + path;
DataOutputStream os = new DataOutputStream(process.getOutputStream());
BufferedReader is = new BufferedReader(new InputStreamReader(new DataInputStream(
        process.getInputStream())), 64);

String inLine;
try {
    StringBuilder sbCommand = new StringBuilder();
    sbCommand.append(command).append(" ");
    sbCommand.append("
");
    os.writeBytes(command.toString());
    if (is != null) {
        for (int i = 0; i < timeout; i++) {
            if (is.ready())
                break;
            try {
                Thread.sleep(5);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        if (is.ready()) {
            inLine = is.readLine();
        } else {
        }
    }

} catch (IOException e) {
    e.printStackTrace();
}

It always stops in is.ready(), and when I changed it to process.waitfor() it also stopped. Why?

Answer 1

As far as i know, the only way to run shell commands is:

Process proc = Runtime.getRuntime().exec("your command");