Unable using Runtime.exec() to execute shell command “echo” in Android Java code

Question

I can use Runtime.exec() to execute shell commands like "getprop" and "ls system" and they work fine.

However, when I use "echo $BOOTCLASSPATH", "echo \\$BOOTCLASSPATH" or "echo HelloWorld", it won't show it in stdout.

The logcat shows:

I/AndroidRuntime( 4453): VM exiting with result code -1.

Here's my code:

try {
    java.lang.Process proc = Runtime.getRuntime().exec("echo -e \\$BOOTCLASSPATH");
    String line = null;

    InputStream stderr = proc.getErrorStream();
    InputStreamReader esr = new InputStreamReader (stderr);
    BufferedReader ebr = new BufferedReader (esr);
    while ( (line = ebr.readLine()) != null )
        Log.e("FXN-BOOTCLASSPATH", line);

    InputStream stdout = proc.getInputStream();
    InputStreamReader osr = new InputStreamReader (stdout);
    BufferedReader obr = new BufferedReader (osr);
    while ( (line = obr.readLine()) != null )
        Log.i("FXN-BOOTCLASSPATH", line);

    int exitVal = proc.waitFor();
    Log.d("FXN-BOOTCLASSPATH", "getprop exitValue: " + exitVal);
} catch (Exception e) {
    e.printStackTrace();
}

Answer 1

@Adi Tiwari, I've found the cause. Runtime.getRuntime.exec() doesn't execute a shell command directly, it executes an executable with arguments. "echo" is a builtin shell command. It is actually a part of the argument of the executable sh with the option -c. Commands like ls are actual executables. You can use type echo and type ls command in adb shell to see the difference.
So final code is:

String[] cmdline = { "sh", "-c", "echo $BOOTCLASSPATH" }; 
Runtime.getRuntime().exec(cmdline);