linux - java Runtime.getRuntime().exec cannot get output for some commands -

i on osx 10.8.5 , trying run terminal commands java.

so code below, can read output of runtime.getruntime().exec commands not others.

you see commands return output fine ls , ifconfig, trying openssl return output either returns nothing or hangs depending on implementation.

i have used 2 different methods of reading output same results both.

what preventing commands returning output?

    thecommand = "ls"; //this command works ok , returns output      //thecommand = "ifconfig"; //this command works ok , returns output      //thecommand = "openssl rand"; //this command not return output      //thecommand = "/bin/sh openssl rand"; //this command not return output      //thecommand = "/bin/sh -c openssl rand"; //this command hangs      try {       system.out.println("trying...");       process extproc=runtime.getruntime().exec(thecommand);       extproc.waitfor();        //read ouput attempt #1 - works okay ls , ifconfig command       //bufferedreader readproc=new bufferedreader(new inputstreamreader(extproc.getinputstream()));       //while(readproc.ready()) {       //  thereadbuffer = readproc.readline();       //  system.out.println(thereadbuffer);       //}        //read output attempt #2 - works okay ls , ifconfig command       inputstream theinputstream = extproc.getinputstream();       java.util.scanner thescanner = new java.util.scanner(theinputstream).usedelimiter("\\a");       if (thescanner.hasnext()) {           thereadbuffer = thescanner.next();           system.out.println(thereadbuffer);       }      } catch( ioexception e) {       system.out.println(e.getmessage());     } catch(interruptedexception e) {       system.out.println(e.getmessage());     } 

i trying generate random characters command (which works in terminal):

openssl rand -hex 6 | sed 's/\(..\)/\1:/g; s/.$//' 

thanks

okay mark w comment original question realized commands output stderr (use geterrorstream) , stdout (use getinputstream).

so doing allows read either:

      bufferedreader readinputproc=new bufferedreader(new inputstreamreader(extproc.getinputstream()));       while(readinputproc.ready()) {         thereadbuffer = readinputproc.readline();         system.out.println(thereadbuffer);       }       bufferedreader readerrorproc=new bufferedreader(new inputstreamreader(extproc.geterrorstream()));       while(readerrorproc.ready()) {         thereadbuffer = readerrorproc.readline();         system.out.println(thereadbuffer);       }