[Q] Read commands' output inside su process - Android Q&A, Help & Troubleshooting

Hello, maybe here someone will help me
I'm writing a file manager app and I want to allow it for browsing with root permissions.
All I have so far is creation of a Process object using Runtime.exec("su"). Then I get output stream from it and write "ls" command. And here goes the question. How to read the output of the "ls"? Getting the input stream from the process gives me stdout of the "su" which is useless.

---

glodos said:
Hello, maybe here someone will help me
I'm writing a file manager app and I want to allow it for browsing with root permissions.
All I have so far is creation of a Process object using Runtime.exec("su"). Then I get output stream from it and write "ls" command. And here goes the question. How to read the output of the "ls"? Getting the input stream from the process gives me stdout of the "su" which is useless.
Click to expand...
Click to collapse
Use the -c option of su:
Code:
su -c 'ls -l /system/'

---

I think I'm closer, but still it doesn't work
I have this:
Code:
p = Runtime.getRuntime().exec("/system/bin/su -c 'ls -d -1 "+directory.getAbsolutePath()+"/*'");
So the command for a directory /data will be:
Code:
/system/bin/su -c 'ls -d -1 /data/*'
But it gives me:
Code:
W/su (13979): request rejected (0->0 'ls)
I have tried putting the command's parts into array but then system asks for su permission on every command. For ex. ls /data needs permission and ls /system needs another permission beacuse the command is different.

---

Not much I can think of to do about that. I had a similar issue once upon a time and I dealt with it by using a script that read its commands from a data file. I'd write the datafile to my program's designated directory (no special permissions required), then run a single command with su and that script would read the datafile to know what to do, otherwise, I had a ****load of su requests bothering the user.

---

You've got a point there, but making it work with a file manager, where the commands are related to user interaction would be very difficult. Anyway I will put it into my consideration.
I wonder how all these root explorers are made but none of the developers, which I asked so far, were so kind to give me some tips

---

glodos said:
You've got a point there, but making it work with a file manager, where the commands are related to user interaction would be very difficult. Anyway I will put it into my consideration.
I wonder how all these root explorers are made but none of the developers, which I asked so far, were so kind to give me some tips
Click to expand...
Click to collapse
Well, I suppose you could keep a process open to a shell with root permissions and once open, keep input and output pipes routed to it and send and receive commands as needed.

---

Gene Poole said:
Well, I suppose you could keep a process open to a shell with root permissions and once open, keep input and output pipes routed to it and send and receive commands as needed.
Click to expand...
Click to collapse
Well, that's what I've tried to do, but as I mentioned in the first post, output pipe gives me stdout of the su process which doesn't write any output (but "ls" does).

---

glodos said:
Well, that's what I've tried to do, but as I mentioned in the first post, output pipe gives me stdout of the su process which doesn't write any output (but "ls" does).
Click to expand...
Click to collapse
No, I don't think you're following me. Just run su -c 'sh' and it should run a shell and keep it open. From there, you create an input stream, output stream and possibly an error stream, then write commands like "ls -l /system\n" (the \n triggers the shell to execute it) to the output stream, then read the results form the input stream. You keep doing this as needed and when you're done just send "exit\n".

---

Oh, I understand now. I'll try it ASAP.
Edit:
It works now, but I have problems with stopping the loop. Here is my piece of code:
Code:
String[] cmd = new String[]{"su", "-c", "/system/bin/sh"};
console = Runtime.getRuntime().exec(cmd);
BufferedWriter stdin = new BufferedWriter(new OutputStreamWriter(console.getOutputStream()));
stdin.write("ls -d -1 "+directory.getAbsolutePath()+"/*\n");
BufferedReader stdout = new BufferedReader(new InputStreamReader(console.getInputStream()));
String read;
data1 = new String();
while((read=stdout.readLine())!=null){
data1+=read + "\n";
}
The problem is, that it hangs at some point on invocation of "stdout.readLine()". I have read that it waits for some data to come and it will never be null.
Furthermore if my ls command returns nothing (which can happen) it always hangs forever on readLine().
Anyway I'll try to do something with this. Maybe there is a workaround and reading will not block.
Thank you for your effort, it was really helpful.

---

glodos said:
The problem is, that it hangs at some point on invocation of "stdout.readLine()". I have read that it waits for some data to come and it will never be null.
Furthermore if my ls command returns nothing (which can happen) it always hangs forever on readLine().
Anyway I'll try to do something with this. Maybe there is a workaround and reading will not block.
Thank you for your effort, it was really helpful.
Click to expand...
Click to collapse
Sorry to ressurect such an old thread. I'd been having the same problem with reads blocking using BufferedReader, InputStream and other variants. Turns out BufferedReader has a ready() method which indicates whether a read() will block. This code works for me:
Code:
String outputStr;
BufferedReader reader = new BufferedReader(new InputStreamReader(suProcess.getInputStream()));
while (reader.ready()) {
outputStr += reader.readLine();
}
Hope it helps someone from the repeating the same frustrations. Heck I hope it helps me in the future in case I forget this