How to get the output inside `screen` out to a script?

Question

I have a screen instance running (a lot more actually, but only one that matters), and I would need to execute some code inside the screen, and get the result out to my script.

The first part is quite easy, I just screen -S session_name -X eval 'stuff "$cmd"\015'.
(I'm no screen expert, I just modified a line I found in a script, but I understand it... Not sure there's no better way to do it, though)

The second part, getting out the output, is trickier. For my current need, I only need the last line, but it'd be better if I can get the whole output, whatever it's size (for future uses).

Answer 1

You could start screen with the -L option. This will cause screen to create a file screenlog.n (the n part is numerical, starting with a zero) in the current working directory.

In your case this would look something like: screen -S session_name -L -X eval 'stuff "$cmd"\015'

As long as you remember to clean up afterwards, this should match what you are after.

For last line of the log, it can easily be obtained with tail -1 screenlog.0, or the entire log can be parsed however you wish.

Answer 2

One more nuance that may be helpful in the future: If you're in a screen session, you can interactively ask for the log file to be created. Use the C-A C-H (Control-A then Control-H) keystroke to ask screen to start dumping whatever window you're in to a log file.