How do I copy the whole history of the clipboard to a text file?

You can see some strings in clipit history file with this command:

strings ~/.local/share/clipit/history

But it's not the best way. The output may be garbled.

there is python script for ClipIt run it like this python cliphist.py > clipit.history.txt

#!/usr/bin/env python
"""cliphist.py: utility to print clipit history file.
If an argument is passed on the command line, it will
be used as a separator, otherwise history items are
separated by a blank line. """

import struct, os, sys

homedir  = os.environ['HOME']
histfile = homedir + '/.local/share/clipit/history'
if len(sys.argv) > 1:
    sep = sys.argv[1]
else:
    sep = '---------------------------------------------------------------------'


with open(histfile,'rb') as f:
    f.read(68)
    size,_ = struct.unpack('2i',f.read(8))
    while (size > 0):
        item = f.read(size)
        print item
        _,_,_,size,_ = struct.unpack('5i',f.read(20))
        if size > 0: 
            print sep

The latest version of Parcellite has a Save As menu item when clicking the icon. This will save all the history entries to a file. There is also a paste all when right-clicking the history list, which will place the entire history list on the clipboard. The preferences have a Paste All delimiter that it will put at the end of each entry.

https://sourceforge.net/projects/parcellite/files/parcellite/parcellite-1.1.1/ ppa here: https://launchpad.net/~rickyrockrat/+archive/ppa

Install KDE's Klipper Clipboard Manager and use the following simple script:

text="nothing yet"
cnt=0
while [ "$text" != "" ]; do
  text=`qdbus org.kde.klipper /klipper getClipboardHistoryItem $cnt`
  echo "==== Clipboard content line $cnt:"
  echo "$text"                      # to terminal output
  echo "$text" > /path/to/file      # to file (EDIT this)
  cnt=$((cnt + 1))
done

Note: This does not behave very well in Unity so it seems. So in other desktop environments than KDE: your mileage may vary.

Modified code from @stepan-shamaiev for Python 3 and without setting of separator:

#!/usr/bin/env python3
"""cliphist.py: utility to print clipit history file."""

import struct, os

homedir  = os.environ['HOME']
histfile = homedir + '/.local/share/clipit/history'

with open(histfile,'rb') as f:
  f.read(68)
  size, _ = struct.unpack('2i', f.read(8))
  while size > 0:
    item = f.read(size)
    print(item.decode())
    _,_,_,size,_ = struct.unpack('5i',f.read(20))
    if size > 0: 
      print('------------------')

user Parcellite, left click on its icon, "clear", select how many times you want, after that, "edit clipboard" and copy it all! Remember so set preference: use primary selection, to make it easier to copy the text!