Screen -X "command"

cramer · 08-25-2006, 12:23 PM

I am looking to use screen to easily access a running program from my perl script, and am interested in using this function listed in the man pages:

Quote:

-X Send the specified command to a running screen session. You can
use the -d or -r option to tell screen to look only for attached
or detached screen sessions. Note that this command doesnât work
if the session is password protected.

I want to send the screen session a command but I am very confused on how to go about using this -X switch. Please help.

theNbomr · 08-25-2006, 12:57 PM

You may be confusing the different acts of sending commands to 'screen' itself, vs. sending commands to the program(s) running in a screen window. It sounds like you want the latter.

You still use the -X option, but accompanied by the 'stuff' command.
An example that might stop a running application...

Code:

screen -X stuff 'exit'

The 'stuff' command is sent to screen, and the argument(s) to the stuff command are entered into the screen window, as if typed at the keyboard. You can embed commands such as this into your perl scripts using the perl 'system()' command.

Hope this helps.

--- rod.

cramer · 08-25-2006, 01:10 PM

That seems to be getting the command to the screen, but it doesn't enter it (Like the user pressing the enter button. Any idea how to get it to simulate an enter key after the command. Also, how do I specify exactly which screen to send it to?

theNbomr · 08-25-2006, 01:23 PM

Usually the enter key sends something like '\r' or '\n' (using perl syntax). That should be part of the string that is 'stuffed'. You specify the screen session with the -S option.

--- rod.

cramer · 08-25-2006, 05:35 PM

I figured I would get that reply, sorry. I already tried the \n \r for carriage returns within the string, it just treats it as part of the string.

Code:

screen -S 4563.kimball.server -X stuff "say red \r"

Anyother ideas for sending a simulated ENTER, expect maybe?

theNbomr · 08-25-2006, 07:54 PM

If you are trying to send the newline from a shell commandline, it is different than from a literal string embedded into perl code.
To send a CR in a bash script, try

Code:

screen -S 4563.kimball.server -X stuff "say red"`echo -ne '\015'`

--- rod.

cramer · 08-25-2006, 09:02 PM

Thanks! It worked out nicely, just enclosed the above command using backticks, and I'll make the -S name a perl variable. Is there anyway to get it so that screen does not place the PID on the session name?

theNbomr · 08-25-2006, 10:48 PM

I think it is always there as part of screen's full name, however I beleive if you open the session with a name, you can reconnect to it by giving that unambiguous name as an identifier. I think...

--- rod.