mjhjmtu

I would like to press a selected hotkey to paste a timestamp in the YYYYMMDDHHmmSS format 20180509145153 immediately, like AutoHotKey allows on Windows.

You could do it at different levels depending on where you want it to happen. For instance, you could configure your shell or prefered text editor to do that, but that would only affect them.

Or you could configure screen/tmux or your terminal emulator to do it and it would affect commands running in that terminal emulator when the terminal emulator is the active window.

Under X11, you could use xbindkey to handle a specific key or key combination and have it simulate a series of keypress and keyrelease events (using xte or xdotool for instance). Which would work for any application connecting to the same X server and is active.

For instance, add to your ~/.xbindkeyrc:

"sleep 0.1; xdotool type --clearmodifiers $(date +%Y%m%d%H%M%S)"
 control+space

For that timestamp to be sent as a series of key press upon Ctrl+Space. (I find that if I don't add the sleep 0.1, I'm sometimes missing the start of the timestamp).

Another option would be to store the timestamp as the PRIMARY X11 selection and simulate a middle mouse button click, which for many application causes the content of the PRIMARY selection to be inserted at the current mouse pointer position. In ~/.xbindkeyrc:

"date +%Y%m%d%H%M%S | tr -d 'n' | xclip; sleep 0.1; exec xdotool click --clearmodifiers 2"
 control+space