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

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);