tcl/tk Observing clipboard

Question

I want to execute a function when something gets put on the clipboard (e.g. strg+c).

How can I observe the clipboard in TCL/TK so that i can handle a notify if something gets on it (event driven).

I did some research and the command after is not quite that what i was looking.

proc observeClipboard {} {

        set lClipboardContent [clipboard get]
        # do something with clipboard content
        after 1000 observeClipboard
}

It doesn't worked as expected and also it wouldn't be an event driven (smoother) solution.

Answer 1

The simplest way is probably to always own the clipboard selection.
This has several downsides: You are responsible for the clipboard, and some clipboard contents might be lost, so this is not bullet-proof.

proc readclip {} {
    after 50 {
        puts [set cnt [clipboard get]]
        clipboard clear
        clipboard append $cnt
        selection own -command readclip -selection CLIPBOARD .
        selection handle . [list string range $cnt]
    }
}
selection own -command readclip -selection CLIPBOARD .

When readclip is invoked, the new application has requested the ownership over the clipboard, but it does not yet have the ownership, so we wait a bit to let it get it, setup everything etc.

Also note that if more than 1 application does this, both applications "battle" over the ownership of the clipboard, which is a bad thing.