Problem with the output of a cmd command in java

Question

I am trying to read in the results of a cmd command (dir for example). After creating the process, I use a BufferedReader in conjunction with an InputStreamReader. For some reason, the BufferedReader keeps coming up empty, even though I know that there must be some output to be read.

Here is the code I'm using:

String[] str = new String[] {"cmd.exe", "/c", 
            "cd", "c:\\",
            "dir", "/b", "/s"               
    };
    Runtime rt = Runtime.getRuntime();
    try{

        Process p = rt.exec(str);
        InputStream is =p.getInputStream();
        System.out.println(is.available());
        InputStreamReader in = new InputStreamReader(is);

        StringBuffer sb = new StringBuffer();
        BufferedReader buff = new BufferedReader(in);
        String line = buff.readLine();
        System.out.println(line);
        while( line != null )
        {
            sb.append(line + "\n");
        System.out.println(line);
            line = buff.readLine();
        }
        System.out.println( sb );
        if ( sb.length() != 0 ){
            File f = new File("test.txt");
            FileOutputStream fos = new FileOutputStream(f);
            fos.write(sb.toString().getBytes());

            fos.close();
        }
    }catch( Exception ex )
    {
        ex.printStackTrace();
    }

yes - both the ErrorStream and InputStream have 0 bytes available — chama
– chama, Commented Feb 4, 2010 at 17:01
I just ran it again, and the error stream is not empty. When I read the error stream, it printed "The system cannot find the path specified," which doesn't exactly make sense, but at least it's something. — chama
– chama, Commented Feb 4, 2010 at 17:05
Try to force the physical address of the file, C:\\test.txt and see what happens — Anthony Forloney
– Anthony Forloney, Commented Feb 4, 2010 at 17:07
Well it could mean that cmd.exe is not in the PATH (or %PATH%, or whatever it's called on windows). Can you try using the full path to the executable, at least for a start ? — phtrivier
– phtrivier, Commented Feb 4, 2010 at 17:08

Trevor Harrison · Accepted Answer · 2010-02-04 17:14:46Z

5

You've got:

String[] str = new String[] {"cmd.exe", "/c", 
            "cd", "c:\\",
            "dir", "/b", "/s"               
    };

which doesn't seem right to me. You can't put multiple commands to cmd.exe on one command line. Thats a batch file.

Try getting rid of everything either the cd or the dir.

edit: indeed:

C:\>cmd.exe /c cd c:\ dir
The system cannot find the path specified.

answered Feb 4, 2010 at 17:14

Trevor Harrison

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2 Comments

chama Over a year ago

That solved the problem! I put an "&" between the cd command and the dir command and got the correct output!

Joey Over a year ago

@chama: What about simply using dir /b /s C:\? Just for the fun of it: Try running your code from another drive, such as D:. Your cd command would do nothing there. Generally, use whatever is applicable and don't try to overcomplicate things. This is an example where you need exactly one command which will do what you want. That sequence of two won't.

Chris Kannon · Accepted Answer · 2010-02-04 17:02:29Z

1

There could be an error. In this case you should also trap getErrorStream()

answered Feb 4, 2010 at 17:02

Chris Kannon

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1 Comment

chama Over a year ago

I tried trapping the ErrorStream and got "The system cannot find the path specified." But how can it not find c:\?

mob · Accepted Answer · 2010-02-04 17:27:05Z

1

The command you are running is cmd.exe /c cd c:\ dir /b /s. I don't think that's doing what you expect.

I mean that you have concatenated two commands into one line and the Windows shell probably doesn't like that. Try something like

String[] str = new String[] {"cmd.exe", "/c", 
            "cd", "c:\\", "&&",
            "dir", "/b", "/s"               
    };

The && will tell the shell to execute cd c:\ and then to execute dir /b /s if the first command was successful.

edited Feb 4, 2010 at 17:27

answered Feb 4, 2010 at 17:16

mob

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1 Comment

chama Over a year ago

that's a very good point. I was originally searching for a certain file in that folder. Unfortunately, taking out the /s didn't solve the problem

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