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Old 04-14-2009, 11:24 PM   #1
jcafaro10
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Registered: Apr 2009
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Running Linux Commands in Java


I'm programming in java on linux trying to have it execute a simple netcat command and print out the results but it refuses to do so. Nothing is printed out so I don't really have any idea if the command is being executed.

Here's my code:
Code:
public static void main(String[] args) throws InterruptedException
	{
		try 
		{
			String result = "";
			String[] commands = new String[]{"/bin/nc.traditional", "www.mywebpage.com", "20000"};
			Process child = Runtime.getRuntime().exec(commands);
			BufferedReader input = new BufferedReader(new InputStreamReader(child.getInputStream()));
		    while ((result = input.readLine()) != null) 
		    {
		    	System.out.println(result);
		    }
		    input.close();
	    } 
		catch (IOException e) 
		{
	    
		}
 
	}
 
Old 04-15-2009, 01:03 AM   #2
1337
Member
 
Registered: Apr 2009
Distribution: Slackware-12.2
Posts: 75

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I am going to assume /bin/nc.traditional is the correct location for netcat on your system. Have you tried passing the arguments to exec as one string rather than an array of strings?

I'm also assuming your not using netcat to get a webpage. Netcat is not designed for retrieving webpages!

Did you get the address and port number right? Is it the right protocol (tcp/udp)? Is the server you are connecting to waiting for a command to be issued first? There are several issues involved here which make it hard for me to help you unless I know more. It would be much better if you told me what the project is, (i.e. what are you trying to do, what kind of server are you connecting to, etc.). This way, I'll be able to help you better.

I suggest you try using "nc example.com 20000 -v -v" (use the v twice) as this will make netcat be of very verbose, thereby letting you know what's going on with the communication.
 
Old 04-15-2009, 11:10 AM   #3
jcafaro10
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Registered: Apr 2009
Posts: 25

Original Poster
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I've tried it as one string and haven't gotten it to work. It's a fake http server that our professor set up for class. I'm trying to connect on a port thats open, just to see if it lets me. I'll take any output at all, I just want to see something printed in the console.

Code:
try 
{
	// Execute a command with an argument
	String result = "";
	String[] commands = new String[]{"/bin/nc.traditional", "www.mywebserver.com", "20000","-v","-v"};
       //String command = "nc www.mywebserver.com 20000 -v -v";
	Process child = Runtime.getRuntime().exec(commands);
	BufferedReader input = new BufferedReader(new InputStreamReader(child.getInputStream()));
        while ((result = input.readLine()) != null) 
	{
   	     System.out.println(result);
	}	    
	input.close();
}
 
Old 04-15-2009, 01:10 PM   #4
1337
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Registered: Apr 2009
Distribution: Slackware-12.2
Posts: 75

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You need to construct an HTTP-header request and send that to netcat's input (using your input stream) before you will get a response from the server. Google HTTP-header to find the format of a request.
 
  


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