[kepler-dev] Running Shell Scripts inside Kepler

[Christopher Brooks]

I found that I needed to create two threads to read from the
Process or else I lost data.

See ptolemy/actor/lib/Exec.java.

About getting stdout, Exec.java does something like:


InputStreamReader _inputStreamReader = new InputStreamReader(process.getInputStream());

                while (((length = _inputStreamReader.read(chars, 0, 80)) != -1)
                        && !_stopRequested && !_stopFireRequested) {
                    _stringBuffer.append(chars, 0, length);
                }

I'm not sure why it is reading in 80 char chunks, it could have
been attempt at providing a more live feeling to reading from the process

_Christopher

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    On Wed, 6 Apr 2005, Dan Higgins wrote:
    
    > Now here is where I ran into trouble!!! On Linux and the Mac, 'R' is a
    > shell script, not a simple executable! And apparently, the Java
    > runtime.exec() method WILL NOT START A SUBPROCESS SET UP THIS WAY WITH A
    > SHELL SCRIPT!!!
    
    The JavaDoc for the 'Process' class contains the following note:
    
      The Runtime.exec methods may not work well for special processes on
      certain native platforms, such as native windowing processes, daemon
      processes, Win16/DOS processes on Microsoft Windows, or shell scripts.
      The created subprocess does not have its own terminal or console. All
      its standard io (i.e. stdin, stdout, stderr) operations will be
      redirected to the parent process through three streams
      (Process.getOutputStream(), Process.getInputStream(),
      Process.getErrorStream()). The parent process uses these streams to feed
      input to and get output from the subprocess.  Because some native
      platforms only provide limited buffer size for standard input and output
      streams, failure to promptly write the input stream or read the output
      stream of the subprocess may cause the subprocess to block, and even
      deadlock.
    
    In my test, executing a shell script worked without problem:
    
    [tobin at robin ~/proving]$ ls
    foo.sh  RunShellScript.class  RunShellScript.java
    
    [tobin at robin ~/proving]$ cat foo.sh
    #!/bin/sh
    echo Hello, World!
    
    [tobin at robin ~/proving]$ cat RunShellScript.java
    
    /* Tobin Fricke
       2005-04-06
    */
    
    class RunShellScript {
      public static void main(String args[]) {
        try {
          Process p = Runtime.getRuntime().exec("./foo.sh");
          /* Note that 'input' and 'output' are from the perspective of the
             controlling Java class.  This 'input stream' refers to the process
   's
             stdout! */
          java.io.InputStream o = p.getInputStream();
          /* Wait for the process to exit. */
          p.waitFor();
          /* Collect its output. */
          int l = o.available();
          byte[] b = new byte[l];
          o.read(b, 0, l);
          System.out.print(new String(b));
        } catch (Exception e) {
          System.out.println("Woops! " + e);
        }
      }
    }
    [tobin at robin ~/proving]$ javac RunShellScript.java
    [tobin at robin ~/proving]$ java RunShellScript
    Hello, World!
    [tobin at robin ~/proving]$
    
    I'd make sure that the R shell script starts with the proper "#!" magic
    cookie & interpreter signture.  Also, does anyone know how to simply dump
    the 'InputStream' obtained from the process to the Java stdout without
    doing the silly byte[] --> String business I did?
    
    Tobin
    
    http://web.pas.rochester.edu/~tobin/
    
    
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