Executing Unix command from java : problem

[SN Hota]

Hi All,

Please check the below program while is not executing, when the
unix command's having \&\& is used.

The following command copies the src folder to dest folder with
out data loss ...

<CODE>

import java.io.*;
import java.util.*;
public class Sample
{
public static void main(String[] args)
{
try {

String ExCmd="ssh

[e-mail] cd /u01/11510/devdb/9.2.0/slax \\&\\&

/bin/tar cf - . | ssh [e-mail] cd

/d01/AppsTest/testappl2 \\&\\& /bin/tar -xf - > test.log";

System.out.println("Command to execute :

"+ExCmd);

Process SshProc =

(Runtime.getRuntime()).exec(ExCmd);

// any error message?
StreamReader errorStream = new

StreamReader(SshProc.getErrorStream(), "DEBUG");

// any output?
StreamReader outputStream = new

StreamReader(SshProc.getInputStream(), "OUTPUT");

// kick them off
errorStream.start();
outputStream.start();

int pp =SshProc.waitFor();
System.out.println("command execution value:

"+pp);

}catch(Exception e) {
e.printStackTrace();
}

}
}

class StreamReader extends Thread
{
InputStream is;
String type;

StreamReader(InputStream is, String type)
{
this.is = is;
this.type = type;
}

public void run()
{
try
{
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line=null;
while ( (line = br.readLine()) != null) {
System.out.println(type + ">" + line);
}
} catch (IOException ioe)
{
ioe.printStackTrace();
}
}
}

</CODE>

When this is executed iam getting process value as "0".

But nothing is copying to target ..

So to resolve this i have created a script .. and passed

arguments to that script and chaged command as follows :

<CODE>
String ExCmd = "sh /home/juser/movedir.sh [e-mail]
/u01/11510/devdb/9.2.0/slax /bin/tar [e-mail]
/d01/AppsTest/testappl2 /bin/tar /home/juser/test";
</CODE>

Then it is executing fine. But in my scenario iam restricted to
use scripts.

So please can any body have a solution for this.

Thanks, SN

[Darryl Burke]

http://forum.java.sun.com/thread.jspa?threadID=5306948

[Rob Spoor]

The reason is simple. Mechanisms like || (execute the second program if the first fails), && (execute the second program if the first succeeds), < (redirect input stream), > (redirect output/error stream) and & (run in background) are interpreted by the SHELL. Java does not execute shell commands but separate commands.

So here's a short way of how to implement them in Java:
- ||: wait until the first program (Process) exits. Check the return code. If it is not 0, execute the second program.
- &&: see || but execute if 0
- <: use the Process' getOutputStream
- >: use the Process' getInputStream and getOutputStream
- 2>&1 (redirect error to output): use ProcessBuilder
- &: execute the program in a different thread

[SN Hota]

Thank you, very much can you please send me a sample code..? It will be helpful for me.

Thanks in advance.

[Rob Spoor]

command1 || command2:

Process p1 = Runtime.getRuntime().exec("command1");
int exitCode = p1.waitFor();
if (exitCode != 0)
{
    Process p2 = Runtime.getRuntime().exec("command2");
}

command1 && command2:

Process p1 = Runtime.getRuntime().exec("command1");
int exitCode = p1.waitFor();
if (exitCode == 0)
{
    Process p2 = Runtime.getRuntime().exec("command2");
}

command < file:

Process p = Runtime.getRuntime().exec("command");
InputStream is = new FileInputStream("file");
OutputStream os = p.getOutputStream();
byte[] buffer = new byte[1024]; // size can be adjusted
int len;
while ((len = is.read(buffer)) != -1)
{
    os.write(buffer);
    os.flush();
}
is.close();
os.close();

You can also use BufferedReader and PrintWriter for reading and writing.

command > file

Process p = Runtime.getRuntime().exec("command");
OutputStream os = new FileOutputStream("file");
InputStream is = p.getInputStream();
byte[] buffer = new byte[1024]; // size can be adjusted
int len;
while ((len = is.read(buffer)) != -1)
{
    os.write(buffer);
    os.flush();
}
is.close();
os.close();

Use getErrorStream to redirect the error stream instead of the output. If you want to redirect both to different files you'll need to redirect both. You'll need to do some threading for that.

command > file 2>&1:

ProcessBuilder builder = new ProcessBuilder("command");
builder.redirectErrorStream(true);
Process p = builder.start();
// now copy as above

As a final note, you should definitely read this article on JavaWorld.com.

[SN Hota]

Thank you...for your quick reply..i will try this.