Below is the working example on windows, it can be adapted for unix as well.
Please try the same on Java before if you would like to troubleshoot. Once it works in Java it is bound to work in pega as well.
 
String[] command = {"C:/Program Files/Java/jdk1.8.0_202/bin/jmap.exe", "-dump:format=b,file=C:/Users/kumau1/Desktop/HeapTest/heapdump2.bin","21544"};
  ProcessBuilder p = new ProcessBuilder(command);
oLog.error("Output of 1111 " + command + " is: ");
   try{ Process p2 = p.start();
       oLog.error("Output of 11112222 " + command + " is: ");
       java.io.BufferedReader br = new java.io.BufferedReader(new java.io.InputStreamReader(p2.getInputStream()));
      
 
    String line;

    oLog.error("Output of running " + command + " is: ");
  
       while ((line = br.readLine()) != null) {
        oLog.error(line);
    }
      }
  
   catch(Throwable t){
  t.printStackTrace();
  }

Thanks for response Ujjwal. But in actual I have got only path where sh file is stored. and my task is to call that script file from Pega. Do you have any working code for that?