java - Can't get output from Runtime.exec() -

i have written code execute command on shell through java:

 string filename="/home/abhijeet/sample.txt";          process contigcount_p;          string command_to_count="grep  \">\" "+filename+" | wc -l";          system.out.println("command counting contigs "+command_to_count);           contigcount_p=runtime.getruntime().exec(command_to_count);            contigcount_p.wait(); 

as pipe symbols being used not able execute command successfully.as per last question's discussion have wrapped variables in shell:

runtime.getruntime().exec(new string[]{"sh", "-c", "grep \">\" "+filename+" | wc -l"});

which worked me executes command on shell , still when try read output using buffered reader :

   bufferedreader reader =                      new bufferedreader(new inputstreamreader(contigcount_p.getinputstream()));      string line=" ";    while((line=reader.readline())!=null)    {        output.append(line+"\n");    } 

it returns null value ,i have found temporary solution have discussed on previous question: link, use right way of doing reading it's output using bufferedreader.

when used command line of {"sh", "-c", "grep \">\" "+filename+" | wc -l"} kept overriding file

i had change quotes double quoted, {"sh", "-c", "grep \"\">\"\" "+filename+" | wc -l"}

so, using contents of test file...

> > >  not new line > 

and using code...

import java.io.bufferedreader; import java.io.ioexception; import java.io.inputstream; import java.io.inputstreamreader;  public class testprocess {      public static void main(string[] args) {         string filename = "test.tx";         string test = "grep \"\">\"\" "+filename+" | wc -l";         system.out.println(test);          try {             processbuilder pb = new processbuilder("sh", "-c", test);             pb.redirecterror();             process p = pb.start();             new thread(new consumer(p.getinputstream())).start();              int ec = p.waitfor();             system.out.println("ec: " + ec);         } catch (ioexception | interruptedexception exp) {             exp.printstacktrace();         }     }      public static class consumer implements runnable {          private inputstream is;          public consumer(inputstream is) {             this.is = is;         }          @override         public void run() {             try (bufferedreader reader =  new bufferedreader(new inputstreamreader(is))){                 string value = null;                 while ((value = reader.readline()) != null) {                     system.out.println(value);                 }             } catch (ioexception exp) {                 exp.printstacktrace();             }         }      }  } 

i able produce output...

grep "">"" test.tx | wc -l 4 ec: 0 

generally, when dealing external processes, it's easier use processbuilder, has nice options, including redirecting error/stdout , setting execution context directory...