无法使用 Runtime.exec() 在 Android Java 代码中执行 shell 命令“echo”
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Unable using Runtime.exec() to execute shell command "echo" in Android Java code
提问by QY Lin
I can use Runtime.exec()to execute shell commands like "getprop" and "ls system" and they work fine.
我可以Runtime.exec()用来执行像“ getprop”和“ ls system”这样的shell命令，它们工作正常。
However, when I use "echo $BOOTCLASSPATH", "echo \\$BOOTCLASSPATH" or "echo HelloWorld", it won't show it in stdout.
但是，当我使用“ echo $BOOTCLASSPATH”、“ echo \\$BOOTCLASSPATH”或“ echo HelloWorld”时，它不会在标准输出中显示。
The logcat shows:
logcat 显示：
I/AndroidRuntime( 4453): VM exiting with result code -1.
Here's my code:
这是我的代码：
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();
}
回答by QY Lin
@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 shwith the option -c.
Commands like lsare actual executables.
You can use type echoand type lscommand in adb shellto see the difference.
So final code is:
@Adi Tiwari，我找到了原因。
Runtime.getRuntime.exec()不直接执行 shell 命令，它执行带参数的可执行文件。" echo" 是一个内置的 shell 命令。它实际上是sh带有选项的可执行文件的参数的一部分-c。类似ls的命令是实际的可执行文件。您可以使用type echo和type ls命令adb shell来查看差异。
所以最终的代码是：
String[] cmdline = { "sh", "-c", "echo $BOOTCLASSPATH" };
Runtime.getRuntime().exec(cmdline);
