In Ubuntu 16 I was able to press Shift PrintScreen and select area on the screen to screenshot it. In Ubuntu 18 when I press Shift PrintScreen the similar mouse icon appears and I also can select an area. But on finish nothing happens, no application appears to have my screenshot inside.
How to restore old functionality?
Note, that I don't want to manually start screenshot
application beforehead and press GUI buttons inside it, I want to have work done on Shift PrintScreen.
The Screenshot tool bundled with Gnome does exactly what you described
It can sreencast too
Screenshot pictures are saved in you default Pictures directory
xdg-user-dir PICTURES
Screencast videos are saved in the home Video directory
xdg-user-dir VIDEOS
Screenshots:
Prt Scrn to take a screenshot of the desktop.
Alt+Prt Scrn to take a screenshot of a window.
Shift+Prt Scrn to take a screenshot of an area you select.
Screencasts:
Ctrl+Alt+Shift+R start recording the desktop.
A red circle is displayed in the top right corner of the screen when the recording is in progress.
Ctrl+Alt+Shift+RStops the recording.
Please read the manual:
https://help.ubuntu.com/stable/ubuntu-help/screen-shot-record.html.en#screenshot
Prt Scrn to take a screenshot of the desktop.
Alt+Prt Scrn to take a screenshot of a window.
Shift+Prt Scrn to take a screenshot of an area you select.
You can also hold down Ctrl with any of the above shortcuts to copy the screenshot image to the clipboard instead of saving it.
After pressing ShiftPrtScr open Files > Recent and you will find the image listed there. Right Click the item and select Open Item Location and that will take you directly to the location where the image is saved.
To answer your question in a single line, the past versions of (Ubunut 16.04 and others) copied the selected grab area in the clipboard with the shortcut key Ctrl+PrtScr, but in case of Ubuntu 18.04 you need to press an extra shift key, i.e.
For those still struggling with this, I found some more answers here: Where are (partial) screenshot stored or how to specifiy location?
What you need to do is open Settings -> Devices -> Keyboard, then scroll down to the Screenshots section. It will show what your shortcut keys are for each action and (if that action is save, rather than copy to clipboard), where the files are being saved. (I tried to find a terminal command for this to cut down on clicks, but didn't.)