Running Perl-Script from Java (embedded in Perl)

Question

Perl accepts a scipt via STDIN. After pressing CTRL-D perl knows the "End of Script". After doing so, the script is executed.

Now my question: I wand to do that from Java.

Open Process Perl
Copy Script into STDIN of Perl-Process
HOW DO I SIGNAL PERL THE CRTL-D WITHOUT CLOSING THE STREAM (from within java)
Send some input to the Script
get some Output from Script.

proc = Runtime.getRuntime().exec("perl", env);
commandChannel = new BufferedWriter(new OutputStreamWriter(proc.getOutputStream()));
responseChannel = new BufferedReader(new InputStreamReader(proc.getInputStream()));
InputStreamReader mymacro = new InputStreamReader(getClass().getResourceAsStream("macro.perl"));

char[] b = new char[1024];
int read;

try
{
    while ((read = mymacro.read(b)) != -1)
    {
        commandChannel.write(b, 0, read);
    }
    commandChannel.flush();
    PERL IS WAITING FOR END OF SCRIPT; ??
}  ...

What happens if you write __END__ to Perl rather than closing STDIN? (or ^D or ^Z -- see perldoc.perl.org/perldata.html#Special-Literals ) — Adrian Pronk
– Adrian Pronk, Commented Nov 2, 2011 at 9:10
I don't know why, but with a small script it works, but with my larger script not... I think I will write the script to a temporary file and load that... — user1025189
– user1025189, Commented Nov 3, 2011 at 8:17

Patrick B. · Accepted Answer · 2011-11-02 08:12:34Z

1

But this exactly what CTRL-D does: closing the STDIN of the process. So in your case closing the proc.getInputStream() is the appropriate action to have the expected behavior as you simulate it in the shell.

If you want to do "something else" just do it. Like writing a special command to your script via STDIN which then interprets it as such and jumps into another state or whatever is desired

answered Nov 2, 2011 at 8:12

Patrick B.

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4 Comments

user1025189 Over a year ago

But when I close the Outputstream (to STDIN of my script), I cannot use it any more. In the Shell it is possible. Run perl. enter als Script $line=<STDIN>; print $line; then CTRL-D ... now the script runs and can echo your input

Patrick B. Over a year ago

Hmm, my java knowledge is a little bit rusty, but when you say OutputStream you mean proc.getOutputStream() or getInputStream()? Because I think that getInputStream is STDIN of your process.

Patrick B. Over a year ago

Make sure that you .write a "\n" (line-break) in your script. This will for $line=<STDIN> to not block anymore.

user1025189 Over a year ago

I tried to run the script via "perl FILENAME" ... works Now I want to embedd the script in a jar file and transfer it to perl via stdin ...

Yotam Madem · Accepted Answer · 2012-02-09 15:14:21Z

1

this example does exactly what you need:

public class TestPl {
public static void main(String[] args) {
  Process proc;
  try {
     proc = Runtime.getRuntime().exec("perl");
     // a simple script that echos stdin.
     String script = "my $s=<>;\n" +
                     "print $s;";

     OutputStreamWriter wr = new OutputStreamWriter(proc.getOutputStream());

     //write the script:
     wr.write(script);

     //signal end of script:
     wr.write(4);
     wr.write("\n");

     //write the input:
     wr.write("bla bla bla!!!");

     wr.flush();
     wr.close();

     String output = readFromInputStream(proc.getInputStream());
     proc.waitFor(); 
     System.out.println("perl output:\n"+output);
  } catch (IOException e) {
     e.printStackTrace();
  } catch (InterruptedException e) {
     e.printStackTrace();
  }
}

public static String readFromInputStream(InputStream inputStream) throws IOException {
  BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
  String line;
  StringBuffer buff = new StringBuffer();
  while ((line=br.readLine())!=null){
     if (buff.length() > 0){
        buff.append("\n");
     }
     buff.append(line);
  }
  br.close();
  return buff.toString();
}

}

edited Feb 9, 2012 at 15:14

answered Feb 9, 2012 at 14:50

Yotam Madem

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4 Comments

user1025189 Over a year ago

I use a temporary file for the Script now. But I'l try your code ... because I don't like temp files. Thanks.

user1025189 Over a year ago

It does not work. The Script should output an "OK" string. I do not get it -> the script is not started correctly... What's wrong?

Yotam Madem Over a year ago

Are you shore the "OK" is written to the STD output? maybe the script writes it to STDERR? I used this code with some SQL conversion scripts and it worked but if you want you can send me an example for not working script and I'll check it.

user1025189 Over a year ago

Yes I am sure, because following works (but is not so optimal): Write Script to Tempfile; Run ´PERL mytempfile´

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