Example Python code, that saves text to the Linux clipboard, persistently.

There are some quirks as to how the Linux X-server clipboard works, which have been observed for some time, but which will also affect how to write a Python script / program, that saves some text to the clipboard, but with the intention that the script should exit immediately, while the copied text should remain on the clipboard.

What works against that, is the way the X11 clipboard works generally, which is, that there is no part of the actual O/S, which stores the clipboard contents. Instead, the application being copied from stores this data, and the data is not transferred until another application, or the same application, pastes it again. This has as consequence, that if the first application tries to store the data to the clipboard but then exits, and if the second application next tries to paste it, the clipboard, by first approximation, will be empty because the first application, which was holding the data, has quit.

There may exist some Linux environments in which the desktop manager takes over in a case like that, to hold a copy of the data that was Copied, but my Debian / Stretch, Plasma 5.8 computer, which I name ‘Phosphene’, fails to do so. And this is also how or why, the Plasma 5 clipboard utility, which is named ‘Klipper’, will sometimes still show that last item at the top of its clipboard history, but why that item cannot be pasted (using <Ctrl>+V), until an earlier item is selected within Klipper, and then the item of interest is selected again, so that this most-recently copied item will actually be available on the clipboard again.

In principle, ‘Klipper’ has a setting which states ‘Assure clipboard never empty’. But, long story short, that setting does not work

(Update 4/09/2019, 6h05 : )

Actually, I have learned an intricacy, of how the Plasma 5, Klipper app interacts with the X11 clipboard, and which I was not aware of before. Apparently, the actual clipboard has 3 ‘slots’: ‘Primary’, ‘Secondary’, and ‘Clipboard’. Mouse-Highlighting will cause ‘Primary’ to point to the selected text, while <Ctrl>+C Copying will cause ‘Clipboard’ to point to the selected text. After that, middle-clicking with the mouse will Paste from ‘Primary’, while <Ctrl>+V will Paste from ‘Clipboard’.

When using <Ctrl>+C, an ideally Linux-compliant application will actually leave with both clipboard targets pointing at the selection, while certain applications such as Firefox will only end up with ‘Clipboard’ pointing at the selected text.

The only real pitfall in understanding ‘Klipper’ was, the fact that while it does keep a copy of the clipboard’s contents ‘on the side’, regardless of how they were Copied, Pasting that copy directly after the application Copied from has closed, is only facilitated for middle-clicking with the mouse, not for the <Ctrl>+V -type Pasting.

However, left-clicking on one of the entries in the Klipper History will cause the ‘Clipboard’ X11 pointer to point to it, unless that just happens to be the most-recent entry.

Basically, the user community wanted an alternative to Windows, that has familiar features, and instead, the Linux developers left them a well-hidden Easter Egg. (:1)


 

I recently needed to install a Python script, which hashes a domain-name, password combination, and which has as feature the ability to save the hash-code ‘to the clipboard’, instead of just printing it out, so that the user should next be able to paste the hash-code, and in some cases do so, without the hash-code ever being displayed. This script failed to work in its original version and I needed to modify it, to get it to work the way I wanted it to work.

(Updated 4/09/2019, 15h40 … )

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