Output redirection with “screen” command

Question

Might be a simple problem, but I am running CentOS 5.4 command line remotely. I want to redirect the output of a simple Java file, lets say loop to print a hundred thousand numbers in console to a text file. The thing is, I have to use the 'screen' command to be able to run it in background even if I loose my session with the remote computer and this command does not write to the desired file.

I tried the method screen java MyClass >& log.txt also screen java MyClass > log.txt but it does not write to the file. Why is this happening and is there any solution?

Answer 1

You can do this with the nohup command. Here's an example.

$ cat Foo.java 
public class Foo {
    public static void main(String[] args) throws InterruptedException
    {
        for(int i = 0 ; i < 1000 ; i++)
        {
            System.out.println(i);
            Thread.sleep(1000);
        }
    }
}

$ javac Foo.java
$ nohup java Foo > foo.txt &
[3] 29542
$ cat foo.txt 
0
1
2
3
4
5
$ exit

<< relaunch shell >>

$ cat foo.txt 
0
1
...
29
30

The reason this doesn't work with screen is because screen doesn't interpret your arguments like the shell does. If you were to do this with screen, it would have worked:

screen /bin/bash -c 'java Foo > foo.txt'

Answer 2

sample_script.sh

#!/bin/bash
#start screen in detached mode with session name 'default_session' 
screen -dmS "default_session"
#redirect output to abc.log 
screen -S default_session -X stuff "script -f /tmp/abc.log\n"
#execute your command
screen -S default_session -X stuff "your command goes here...\n"