Among the many reasons I use iTerm2 in lieu of the macOS Terminal is its AppleScript support.

I recently had the need to automate some tasks on my Amazon Web Services EC2 server in a way that takes advantage of iTerm2 AppleScript functionality.

Use case

I’ve found recently, that my screen sessions were disappearing. Although I haven’t completely excluded other causes, some have suggested that infrequently-reconnected sessions can be cleaned up. Since I’m not a Unix sysadmin, I’m not sure about this. However, I decided to test the hypothesis by writing an AppleScript that logs into my EC2 server, attaches to each screen session, detaches and closes the connection.

screen escape sequence implementation

The trickiest bit to solve was the ^A escape sequence that screen uses. Here’s how I solved that part:

key code 0 using {control down}
delay 1
keystroke "d"

By wrapping that in a subroutine, I was able to automate the detachment from the current screen.

Full implementation

The complete implementation just loops over the screen session ID’s, attaches and detaches then finally logs out and closes the window. I use LaunchControl to have the AppleScript run every 2 hours.

--
--	Created by: Alan Duncan
--	Created on: 2017-02-02
--
--	Copyright (c) 2017 OjisanSeiuchi
--	All Rights Reserved
--

use AppleScript version "2.4" -- Yosemite (10.10) or later
use scripting additions

set screenIDs to {5546, 5208, 5129, 5580}

tell application "iTerm"
	set newWindow to (create window with profile "OjisanSeiuchi EC2")
	tell current session of current window
		delay 3
		repeat with screenID in screenIDs
			-- attach to this screen session
			set screenCommand to "screen -r " & (screenID as string)
			write text screenCommand
			delay 2
			--	detach from the session
			my detach()
			delay 1
		end repeat
		write text "logout"
		delay 1
	end tell
	close newWindow
end tell

--	detaches from the current screen session
on detach()
	tell application "iTerm" to activate
	tell application "System Events"
		tell process "iTerm2"
			key code 0 using {control down}
			delay 1
			keystroke "d"
		end tell
	end tell
end detach

We’ll see if this solves the problem of screen sessions disappearing.