Execute "echo $BASHPID" in Linux using Java

[Erik Deveza]

Hi, I am new to programming Java in Linux environment.

I need to get to execute "echo $BASHPID" in the terminal console of Linux and get the value returned.

I tried the following codes:

String[] cmd = {"echo $BASHPID"};
Process process = Runtime.getRuntime().exec(cmd) ;  
InputStream is = process.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line = br.readLine();
System.out.println(line);
br.close();
isr.close();
is.close();
long sessionId = Long.parseLong(line);

however, an error occurs when I execute the program. It does not recognized "echo $BASHPID". It throws "java.io.IOException: Cannot run program "echo $BASHPID": java.io.IOException: error=2, No such file or directory." Did I miss out a command function?

[Stephan van Hulst]

Hi Erik. Take some time to read what the java.lang.Runtime documentation says on the various exec() methods.

Note that exec() does not work like the command prompt.

[Erik Deveza]

Thanks for reminding me. I got the solution. I changed it to ProcessBuilder.

Vector<String> commands=new Vector<String>();  
commands.add("/bin/bash");  
commands.add("-c");  
commands.add("echo $BASHPID");  
ProcessBuilder p=new ProcessBuilder(commands);  
Process process = p.start();  
InputStream is = process.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line = br.readLine();
System.out.println("BASHPID=" + line);
sessionId = Long.parseLong(line);
br.close();
isr.close();
is.close();

[Henry Wong]

I don't see the value of this code... you are starting a new shell (bash), so you can ask the shell, what is its PID? What does that serve? The shell will terminate upon completion, so the PID is now for a terminated application. What can you do with the PID?

Henry

[Erik Deveza]

Henry Wong wrote:
I don't see the value of this code... you are starting a new shell (bash), so you can ask the shell, what is its PID? What does that serve? The shell will terminate upon completion, so the PID is now for a terminated application. What can you do with the PID?

Henry

Thanks, Henry, for pointing this one out. I am new to programming in Linux. I am trying to get the session id of a user in Linux. Would you know how to execute BASHPID in such a way that it gets the PID of the currently active user?

[Ernie Mcracken]

Are you sure $BASHPID is really what you want, this gives your the process ID of the current shell. Maybe you want $UID the current user id?

Also $BASHPID is just an environment variable so you can't "execute" it just get its value

[Erik Deveza]

Ernie Mcracken wrote:Are you sure $BASHPID is really what you want, this gives your the process ID of the current shell. Maybe you want $UID the current user id?

Also $BASHPID is just a system variable so you can't "execute" it just get its value

Thanks Ernie for dropping your comment! $UID is the current user id? I was hoping to get the user's session id. I was just thinking of this scenario: If there are 2 users using the same username and logs in from 2 remote machines to a separate Linux machine, their session user id will be their identifier because both would only return a single $UID. Would you happen to know how to get the user's session id?

[Ernie Mcracken]

tty should give you a unique for every value instance of a login to a shell regardless of it the UID is the same (i think).