Save Screen (program) output to a file

Question

There is a command line option for logging. The output is saved to screenlog.n file, where n is a number of the screen. From man pages of screen:

‘-L’ Tell screen to turn on automatic output logging for the windows.

You can also use Control-a + H to save loggings into screenlog.n file. One more Control-a + H to turn off.

C-a H: Begins/ends logging of the current window to the file "screenlog.n".

The following command works for Screen version 4.06.02:

screen -L -Logfile Log_file_name_of_your_choice command_to_be_executed

From the man page of Screen:

-Logfile file : By default logfile name is "screenlog.0".
                You can set new logfile name with the "-Logfile" option.

You can check the existing version of Screen using screen -version. You can download and install the latest Screen version from https://www.gnu.org/software/screen/.

The selected answer doesn't work quite well with multiple sessions and doesn't allow to specify a custom log file name.

For multiple screen sessions, this is my formula:

1. Create a configuration file for each process:

   logfile test.log
   logfile flush 1
   log on
   logtstamp after 1
   logtstamp string "[ %t: %Y-%m-%d %c:%s ]\012"
   logtstamp on
   

   If you want to do it "on the fly", you can change logfile automatically. \012 means "new line", as using \n will print it on the log file: source.

2. Start your command with the "-c" and "-L" flags:

   screen -c ./test.conf -dmSL 'Test' ./test.pl
   

   That's it. You will see "test.log" after the first flush:

   ...
   6 Something is happening...
   [ test.pl: 2016-06-01 13:02:53 ]
   7 Something else...
   [ test.pl: 2016-06-01 13:02:54 ]
   8 Nothing here
   [ test.pl: 2016-06-01 13:02:55 ]
   9 Something is happening...
   [ test.pl: 2016-06-01 13:02:56 ]
   10 Something else...
   [ test.pl: 2016-06-01 13:02:57 ]
   11 Nothing here
   [ test.pl: 2016-06-01 13:02:58 ]
   ...
   

I found that "-L" is still required even when "log on" is on the configuration file.

I couldn't find a list of the time format variables (like %m) used by screen. If you have a link of those formats, please post it bellow.

Extra

In case you want to do it "on the fly", you can use this script:

#!/bin/bash
if [[ $2 == "" ]]; then
    echo "Usage: $0 name command";
    exit 1;
fi
name=$1
command=$2
path="/var/log";
config="logfile ${path}/${name}.log
logfile flush 1
log on
logtstamp after 1
logtstamp string \"[ %t: %Y-%m-%d %c:%s ]\012\"
logtstamp on";
echo "$config" > /tmp/log.conf
screen -c /tmp/log.conf -dmSL "$name" $command
rm /tmp/log.conf

To use it, save it (screen.sh) and set +x permissions:

./screen.sh TEST ./test.pl

... and will execute ./test.pl and create a log file in /var/log/TEST.log

For the Mac terminal:

script -a -t 0 out.txt screen /dev/ttyUSB0 115200

Details

• script: A built-in application to "make a typescript of terminal session"
• -a: Append to output file
• -t 0: Time between writing to output file is 0 seconds, so out.txt is updated for every new character
• out.txt: Is just the output file name
• screen /dev/ttyUSB0 115200: Command from question for connecting to an external device

You can then use tail to see that the file is updating.

tail -100 out.txt

Ctrl+A then Shift+H works for me. You can view the file screenlog.0 while the program is still running.

A different answer if you need to save the output of your whole scrollback buffer from an already actively running screen:

Ctrl-a [ g SPACE G $ >.

This will save your whole buffer to /tmp/screen-exchange