Executing terminal commands from java

Question

I know there are many threads about this, but none of them worked for me. Here is what I am trying to do:

Javac and run a file from my java code. It works for Windows but I would like to make it also work on UNIX. Here the code:

if(os.equals("win")){
 //For Windows
 try {
 Runtime.getRuntime().exec(
 "cmd /c start cmd.exe /K "
 + "\"cd " + path + "&& "
 + "javac " + name + ".java && "
 + "echo ^>^>" + name + ".java " + "outputs: &&"
 + "echo. &&"
 + "java " + name + " && "
 + "echo. &&"
 + "pause && "
 + "exit\"");
 } catch (IOException e) {
 System.out.println("Didn't work");
 }
 }else{
 try {
 //TODO make it work for UNIX
 Runtime.getRuntime().exec("");
 } catch (IOException e) {
 System.out.println("Didn't work");
 }
 }

The problem is, that on UNIX systems it acts "unpredictable" For exemple:

Runtime.getRuntime().exec("open image.png");

Opens the image but

Runtime.getRuntime().exec("javac Test.java");
Runtime.getRuntime().exec("echo 'hello'");

It does nothing. No Massage.

I am grateful for any input.

UPDATE------------------------------------------------------------

It seems like in contrast to Windows CMD, Terminal needs a InputStreamReader to display what happened in exec. I found this code in another thread and now at least I get some output from the exec Terminal.

 String line;
 Process p = Runtime.getRuntime().exec( "echo HelloWorld2" );
 BufferedReader in = new BufferedReader(
 new InputStreamReader(p.getInputStream()) );
 while ((line = in.readLine()) != null) {
 System.out.println(line);
 }
 in.close();

But things still remain misterious, because executing

Process p = Runtime.getRuntime().exec("javac Test.java");

works and generates a Test.class file. But

Process p = Runtime.getRuntime().exec("javac Test.java && java Test");

does nothing.(Nothing happens. Terminal "executes" without error massages.) Typing this manually in Terminal builds and runs as expected. What am I missing?

• Reinstate Monica -- notmaynard: In what way does it not work? What is the output you're getting? What are you expecting?
• AlexR: What does it mean "won't work?" Can you share the exception stack trace with us?
• Haeri: Won't work = It just doesn't execute the command. From the example Runtime.getRuntime().exec("javac Test.java"); it does not generate a Test.class.
• BarrySW19: Runtime.exec() returns a Process object which has the stdout and stderr streams available - reading these should give you any OS generated error messages.
• Haeri: Ok. Interesting. Because on windows all error messages directly got displayed in the cmd window.

Answer 1

I don't have a Linux system here to play with, but I'm pretty certain that the second command above is trying to compile Java files named "Test.java", "&&", "java" and "Test"; in other words the Runtime.exec() method treats arguments literally instead of applying shell interpretation.

You could probably get it to work with something along the lines of:

Process p = Runtime.getRuntime().exec(
 new String[] { "sh", "-c", "javac Test.java && java Test" });

• Haeri: Almost! Things work! I can string my commands together now. But one more thing. Test.java has a System.out.println("worked!"); But that does not display anywhere.. (In windows every I/O, even if it is from the just compiled and executed file, get displayed in the same cmd window.) Here the I/O from the compiled file(Test.class) do not show up.
• BarrySW19: That output should be going into the stdout stream you get from the Process object returned by the exec() call.