java - Runtime.getRuntime().exec using PIPE in command -

i'm trying create splitted tar file , reading progress checking size of directory. (i cannot use pv command).

can explain me why if in tarservice.java change command to:

string cmd="su -c tar -cp -c /dev . | split -b 1g -a 3 - "+ fname; 

the process in mainactivity never log until other process finished, while with:

string cmd="su -c tar -cpf " + fname + " -c /dev ."; 

it works!

take care in both cases tar file created.

mainactivitiy.java

    public void startbackup(view v){         back= new backgroundtask().execute();      }      private class backgroundtask extends asynctask<void, integer, string> {           @override         protected string doinbackground(void... arg0) {             backup = new intent(mainactivity.this, tarservice.class);             backup.putextra("fname", "test.tar);                 status=999;             startservice(backup);             while (status == 999) {                         try {                             process process = runtime.getruntime().exec("du -sk /dev");                             bufferedreader bufferedreader = new bufferedreader(                                     new inputstreamreader(process.getinputstream()));                             string line;                             while ((line = bufferedreader.readline()) != null) {                                 log.d(tag,line);                             }                         }             }         }      } 

tarservice.java

protected void onhandleintent(intent i) {         try{             location=i.getstringextra("location");             fname=i.getstringextra("fname");             // works             string cmd="su -c tar -cpf " + fname + " -c /dev .";             process process = runtime.getruntime().exec(cmd);             int code=process.waitfor();             intent intent = new intent("backupprocess");             intent.putextra("status", code);             log.d(tag,integer.tostring(code));             localbroadcastmanager.getinstance(this).sendbroadcast(intent);         } catch (ioexception e) {             log.e(tag, e.getmessage());             throw new runtimeexception(e);         }  } 

solved

there code error, passing du command file name too, split filename different.

exec() doesn't start shell, doesn't understand shell syntax redirections , pipes. if use shell syntax have start shell, via sh -c ....