I need to run screen from a script

DavidHB · 12-16-2006, 12:46 PM

I need to run "screen" from a script. Is it possible? Is a there a substitue?

What I need to do is start a session run a program and then remotely be able to connect to that session and see the stdout results. Needs to be in real time, so having the program write to a file and then read the file remotely from another console doesn't do it.

???

Dave

macemoneta · 12-16-2006, 01:17 PM

TCL/Expect was made for this. You can use screen as part of the process. For example:

Code:

#!/usr/bin/expect
set error 0

spawn -noecho /usr/bin/ssh user@host

expect "$ "
after 1000
send "screen\r"

expect {
   "$ " {
      after 1000
      send "ls\r"
   }
   timeout {
      set error 1
   }
}

after 1000
send "\01\04"

exit $error

This will connect via ssh to user@host, run screen, issue the command 'ls' and disconnect. When you reconnect to the session, you will see the output of the 'ls command.

Update: I changed the code to not wait for the completion of the command ("ls" in the example), since I think you want to use this to start a long running command.

trickykid · 12-16-2006, 10:59 PM

Why not just launch the screen session in a detached mode?

From the man page:

Code:

-d -m      Start screen in "detached" mode. This creates a new session but doesn't attach to it. This is useful for system startup scripts.

/usr/bin/ssh user@host /usr/bin/screen -d -m /path/to/command

The only downside to this is if the command you execute terminates, it will kill the screen session. But if it's a command that is long running or running a continuous daemon or service, shouldn't give you too much problems as easy way to start the screen and come back to it later to see what's going on if there's console output.