[logging] Save Screen (program) output to a file

I need to save the whole output of Screen to a file to check later all the content.

The reason is that I'm dumping a flash memory through a serial port, using Screen to interface with it. I would like to save it to a file to check memory structure.

I've tried:

$: screen /dev/ttyUSB0 115200 >> foo.txt
$: screen /dev/ttyUSB0 115200 | tee foo.txt

And I've also tried to use bufferfile from screen, but I don't understand how to use it.

Is there an easy way?

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

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

The following might be useful (tested on: Linux/Ubuntu 12.04 (Precise Pangolin)):

cat /dev/ttyUSB0

Using the above, you can then do all the re-directions that you need. For example, to dump output to your console while saving to your file, you'd do:

cat /dev/ttyUSB0 | tee console.log

Here's a trick: wrap it in sh -c!

screen sh -c './some-script 2>&1 | tee mylog.log'

Where 2>&1 redirects stderr to stdout so tee can catch and log error messages.

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

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

The 'script' command under Unix should do the trick. Just run it at the start of your new console and you should be good.

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/.

Existing screen log can be saved by :

Ctrl+A : hardcopy -h filename

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".