Copying the GNU screen scrollback buffer to a file (extended hardcopy)

TL;DR: ^A:writebuf <filename>

The OP seems to want a way to use the selected portion of the buffer you get when doing a ^A[ , selecting text using space as the start and finish, and then instead of using ^A] to paste, save the resulting selected portion of the buffer to a file.

This worked:

^A:writebuf <filename>

Note: one 'f' in writebuf

Press Ctrl+A :bufferfile /tmp/somefile.txt ENTER, and then Ctrl+A >

This will write the current contents of the buffer to the named file.

To write the entire contents of the scrollback buffer to a file, type

Ctrl + A and : to get to command mode, then

hardcopy -h <filename>

In older versions of screen, if you just do hardcopy -h, it just writes to the file -h. This was fixed in version 4.2.0, so hardcopy -h writes to hardcopy.N where N is the current window number.